Showing papers in "Experimental Physiology in 2014"

Purinergic signalling: from discovery to current developments

Abstract: New Findings • What is the topic of this review?This is a personal historical review about the discovery and the main conceptual advances leading to our current understanding of purinergic signalling. The contributions of leading figures in the field are acknowledged. It includes the discovery of purinergic neuromuscular and synaptic transmission, cotransmission, the identification of P1 (adenosine), P2X nucleotide ion channel and P2Y nucleotide G protein-coupled receptors, the identity of ectonucleotidases and release of ATP from cells by mechanical stimulation and mechanosensory transduction. • What advances does it highlight?It highlights the pathophysiology of purinergic signalling and recent therapeutic developments. This lecture is about the history of the purinergic signalling concept. It begins with reference to the paper by Paton & Vane published in 1963, which identified non-cholinergic relaxation in response to vagal nerve stimulation in several species, although they suggested that it might be due to sympathetic adrenergic nerves in the vagal nerve trunk. Using the sucrose gap technique for simultaneous mechanical and electrical recordings in smooth muscle (developed while in Feldberg's department in the National Institute for Medical Research) of the guinea-pig taenia coli preparation (learned when working in Edith Bulbring's smooth muscle laboratory in Oxford Pharmacology), we showed that the hyperpolarizations recorded in the presence of antagonists to the classical autonomic neurotransmitters, acetylcholine and noradrenaline, were inhibitory junction potentials in response to non-adrenergic, non-cholinergic neurotransmission, mediated by intrinsic enteric nerves controlled by vagal and sacral parasympathetic nerves. We then showed that ATP satisfied the criteria needed to identify a neurotransmitter released by these nerves. Subsequently, it was shown that ATP is a cotransmitter in all nerves in the peripheral and central nervous systems. The receptors for purines and pyrimidines were cloned and characterized in the early 1990s, and immunostaining showed that most non-neuronal cells as well as nerve cells expressed these receptors. The physiology and pathophysiology of purinergic signalling is discussed.

Exogenously Applied Muscle Metabolites Synergistically Evoke Sensations of Muscle Fatigue and Pain in Human Subjects

Abstract: The perception of fatigue is common in many disease states, however, the mechanisms of sensory muscle fatigue are not understood. In mice, rats and cats, muscle afferents signal metabolite production in skeletal muscle using a complex of ASIC, P2X and TRPV1 receptors. Endogenous muscle agonists for these receptors are combinations of protons, lactate, and ATP. Here we applied physiological concentrations of these agonists to muscle interstitium in human subjects to determine if this combination could activate sensations, and if so determined how these subjects described these sensations. Ten volunteers received infusions (0.2 ml over 30-s) containing protons, lactate and ATP under the fascia of a thumb muscle, abductor pollicis brevis (APB). Infusion of individual metabolites at maximum amounts evoked no fatigue or pain. Metabolite combinations found in resting muscles (pH 7.4+300nM ATP+1mM lactate) also evoked no sensation. The infusion of a metabolite-combination found in muscle during moderate endurance-exercise (pH 7.3+400nM ATP+5 mM lactate) produced significant fatigue sensations. Infusion of a metabolite-combination associated with vigorous exercise (pH 7.2+500nM ATP+10mM lactate) produced stronger sensations of fatigue and some ache. Higher levels of metabolites (as found with ischemic exercise) caused more ache but no additional fatigue-sensation. Thus, in a dose-dependent manner, intramuscular infusion of combinations of protons, lactate, and ATP leads to fatigue-sensation and eventually pain, probably through activation of ASIC, P2X, and TRPV1 receptors. This is the first demonstration in humans that metabolites normally produced by exercise act in combination to activate sensory neurons that signal sensations of fatigue and muscle pain.

Structure and function of voltage‐gated sodium channels at atomic resolution

Abstract: New Findings • What is the topic of this review?The central goal of the research reviewed here is to understand the functional properties of voltage-gated sodium channels at the level of high-resolution structure of the channel protein. • What advances does it highlight?The key functional properties of voltage-gated sodium channels, including voltage-dependent activation. Sodium conductance and selectivity, block by local anesthetics and related drugs, and both fast and slow inactivation, are now understood at the level of protein structure with high resolution. These emerging high-resolution structural models may lead to development of safer and more efficacious drugs for treatment of epilepsy, chronic pain, and cardiac arrhythmia through structure-based drug design. Voltage-gated sodium channels initiate action potentials in nerve, muscle and other excitable cells. Early physiological studies described sodium selectivity, voltage-dependent activation and fast inactivation, and developed conceptual models for sodium channel function. This review article follows the topics of my 2013 Sharpey-Schafer Prize Lecture and gives an overview of research using a combination of biochemical, molecular biological, physiological and structural biological approaches that have elucidated the structure and function of sodium channels at the atomic level. Structural models for voltage-dependent activation, sodium selectivity and conductance, drug block and both fast and slow inactivation are discussed. A perspective for the future envisions new advances in understanding the structural basis for sodium channel function and the opportunity for structure-based discovery of novel therapeutics.

Mitochondrial function/dysfunction in white adipose tissue

Abstract: The role of mitochondria in white adipocytes has long been neglected due in part to their lower abundance in these cells. However, accumulating evidence suggests that mitochondria are vital for maintaining metabolic homeostasis in white adipocytes because of their involvement in adipogenesis, fatty acid synthesis and esterification, branched-chain amino acid catabolism and lipolysis. It is therefore not surprising that white adipose tissue function can be perturbed by altering mitochondrial components or oxidative capacity. Moreover, studies in humans and animals with significantly altered fat mass, such as in obesity or lipoatrophy, indicate that impaired mitochondrial function in adipocytes may be linked directly to the development of metabolic diseases such as diabetes and insulin resistance. However, recent studies that specifically targeted mitochondrial function in adipocytes indicated dissociation between impaired mitochondrial oxidative capacity and systemic insulin sensitivity.

Intermittent and continuous high-intensity exercise training induce similar acute but different chronic muscle adaptations

Abstract: New Findings What is the central question of this study? How important is the interval in high-intensity interval training (HIIT)? What is the main finding and its importance? The intermittent nature of HIIT is important for maximizing skeletal muscle adaptations to this type of exercise, at least when a relatively small total volume of work is performed in an ‘all-out’ manner. The protein signalling responses to an acute bout of HIIT were generally not predictive of training-induced outcomes. Nonetheless, a single session of exercise lasting <10 min including warm-up, performed three times per week for 6 weeks, was sufficient to improve maximal aerobic capacity. High-intensity interval training (HIIT) performed in an ‘all-out’ manner (e.g. repeated Wingate tests) is a time-efficient strategy to induce skeletal muscle remodelling towards a more oxidative phenotype. A fundamental question that remains unclear, however, is whether the intermittent or ‘pulsed’ nature of the stimulus is critical to the adaptive response. In study 1, we examined whether the activation of signalling cascades linked to mitochondrial biogenesis was dependent on the manner in which an acute high-intensity exercise stimulus was applied. Subjects performed either four 30 s Wingate tests interspersed with 4 min of rest (INT) or a bout of continuous exercise (CONT) that was matched for total work (67 ± 7 kJ) and which required ∼4 min to complete as fast as possible. Both protocols elicited similar increases in markers of adenosine monophosphate-activated protein kinase (AMPK) and p38 mitogen-activated protein kinase activation, as well as Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) mRNA expression (main effects for time, P ≤ 0.05). In study 2, we determined whether 6 weeks of the CONT protocol (3 days per week) would increase skeletal muscle mitochondrial content to a similar extent to what we have previously reported after 6 weeks of INT. Despite similar acute signalling responses to the CONT and INT protocols, training with CONT did not increase the maximal activity or protein content of a range of mitochondrial markers. However, peak oxygen uptake was higher after CONT training (from 45.7 ± 5.4 to 48.3 ± 6.5 ml kg−1 min−1; P < 0.05) and 250 kJ time trial performance was improved (from 26:32 ± 4:48 to 23:55 ± 4:16 min:s; P < 0.001) in our recreationally active participants. We conclude that the intermittent nature of the stimulus is important for maximizing skeletal muscle adaptations to low-volume, all-out HIIT. Despite the lack of skeletal muscle mitochondrial adaptations, our data show that a training programme based on a brief bout of high-intensity exercise, which lasted <10 min per session including warm-up, and performed three times per week for 6 weeks, improved peak oxygen uptake in young healthy subjects.

Cortical control of the autonomic nervous system.

Abstract: New Findings What is the topic of this review? The pathways in the brain by which visceral information, in particular cardiopulmonary afferents, ascend to the cerebral cortex have been delineated in animal models. Studies using functional magnetic resonance imaging in humans have confirmed what was known from the animal studies and established the critical sites in the cerebral cortex of humans for autonomic control and the significance of these sites for cognitive emotional function. What advances does it highlight? Stimulation of cardiopulmonary afferents in humans has consistently resulted in activation in the insular cortex and the anterior cingulate cortex. It has been shown that individuals who are characterized as cardiovascular responders to mental stress have a different pattern of activity in the cortex related to the cardiac changes. A number of animal studies in the rat and cat have been particularly useful for determining the pathways and the sites in the forebrain and cortex that are responsible for autonomic control. For example, these experiments have demonstrated that there is a viscerotopically organized pathway, with the first site of termination in the nucleus of the solitary tract and with subsequent relays in the parabrachial nucleus and the ventroposterior parvocellular nucleus of the thalamus before final visceral afferent inputs in the insular cortex. Several neuroimaging studies in humans, using cardiopulmonary manipulations, have confirmed the importance of the insular cortex as a site of for visceral afferent inputs. The anterior cingulate cortex has also been implicated in cardiopulmonary control. Both the insular cortex and the infralimbic cortex have been shown to be involved in descending control of the cardiovascular system. Neuroimaging with functional magnetic resonance imaging has demonstrated that the cortical autonomic control pathways are different in individuals who are characterized as cardiovascular reactors to mental stress. There is evidence that this alteration in pathways in the cortex may be due to past experiences, including childhood trauma.

Assessment of myometrial transcriptome changes associated with spontaneous human labour by high-throughput RNA-seq.

Abstract: The transition of the human uterus from a quiescent to a contractile state takes place over a number of weeks. On such biological time scales, cellular phenotype is modified by changes in the transcriptome, which in turn is under the control of the underlying endocrine, paracrine, and biophysical processes resulting from the ongoing pregnancy. In this study, we characterize the transition of the human myometrial transcriptome at term from not in labour (NIL) to in labour (LAB) using high throughput RNA sequencing (RNA-seq). RNA was isolated from the myometrium of uterine biopsies from patients at term who were not in labour (n = 5) and at term in spontaneous labour (n = 5) without augmentation. A total of 143.6 million separate reads were sequenced, achieving, on average, ∼13 times coverage of the expressed human transcriptome per sample. Principal component analysis indicated that the NIL and LAB transcriptomes could be distinguished as two distinct clusters. A comparison of the NIL and LAB groups, using three different statistical approaches (baySeq, edgeR, and DESeq), demonstrated an overlap of 764 differentially expressed genes. A comparison with currently available microarray data revealed only a partial overlap in differentially expressed genes. We conclude that the described RNA-seq data sets represent the first fully annotated catalogue of expressed mRNAs in human myometrium. When considered together, the full expression repertoire and the differentially expressed gene sets should provide an excellent resource for formulating new hypotheses of physiological function, as well as the discovery of novel therapeutic targets.

The rhythms of life: what your body clock means to you!

Abstract: Until we turned our nights into days and began to travel in aircraft across multiple time zones, we were largely unaware that we possess a 'day within' driven by an internal body clock. Yet the striking impairment of our abilities in the early hours of the morning soon reminds us that we are slaves to our biology. Our ability to perform mathematical calculations or other intellectual tasks between 04.00 and 06.00 h is worse than if we had consumed several shots of whisky and would be classified as legally drunk. Biological clocks drive or alter our sleep patterns, alertness, mood, physical strength, blood pressure and every other aspect of our physiology and behaviour. Our emerging understanding of how these 24 h rhythms are generated and regulated is not only one of the great success stories of modern biology, but is also informing many areas of human health. Sleep and circadian rhythm disruption (SCRD) is a feature shared by some of the most challenging diseases of our time, including neuropsychiatric illness and serious disorders of the eye. Sleep and circadian rhythm disruption is also commonly seen across many sectors of society, from teenagers to shift workers. We also now appreciate that SCRD is far more than feeling sleepy at an inappropriate time. It promotes multiple illnesses ranging across abnormal metabolism, heart disease, reduced immunity, increased stress and abnormal cognition and mood states. This short review considers how 24 h rhythms are generated and regulated, the consequences of working against our body clock and the emerging relationship between SCRD and mental illness.

Dynamics of corticospinal changes during and after high-intensity quadriceps exercise

Abstract: This study tested the hypothesis that during fatiguing quadriceps exercise, supraspinal fatigue develops late, is associated with both increased corticospinal excitability and inhibition and recovers quickly. Eight subjects performed 20 s contractions [15 s at 50% maximal voluntary contraction (MVC) followed by 5 s MVC] separated by a 10 s rest period until task failure. Transcranial magnetic stimulation (TMS) and electrical femoral nerve stimulation (PNS) were delivered ∼ 2 s apart during 50% MVC, during MVC and after MVC in relaxed muscle. Voluntary activation was assessed by TMS (VATMS) immediately before and after exercise and then three times over a 6 min recovery period. During exercise, MVC and twitch force evoked by PNS in relaxed muscle decreased progressively to 48 ± 8 and 36 ± 16% of control values, respectively (both P < 0.01). Significant changes in voluntary activation assessed by PNS and twitch evoked by TMS during MVC were observed during the last quarter of exercise only (from 96.4 ± 1.7 to 86 ± 13%, P = 0.03 and from 0.76 ± 0.8 to 4.9 ± 4.7% MVC, P = 0.02, from baseline to task failure, respectively). The TMS-induced silent period increased linearly during both MVC (by ∼ 79 ms) and 50% MVC (by ∼ 63 ms; both P < 0.01). Motor-evoked potential amplitude did not change during the protocol at any force levels. Both silent period and VATMS recovered within 2 min postexercise, whereas MVC and twitch force evoked by PNS in relaxed muscle recovered to only 84 ± 9 and 73 ± 17% of control values 6 min after exercise, respectively. In conclusion, high-intensity single-joint quadriceps exercise induces supraspinal fatigue near task failure, with increased intracortical inhibition and, in contrast to previous upper-limb results, unchanged corticospinal excitability. These changes recover rapidly after task failure, emphasizing the need to measure corticospinal adaptations immediately at task failure to avoid underestimation of exercise-induced corticospinal changes.

Physiology of invertebrate oxytocin and vasopressin neuropeptides.

Abstract: Neuropeptides and regulatory peptide hormones control many developmental, physiological and behavioural processes in animals, including humans. The nonapeptides oxytocin and arginine vasopressin are produced and released by the pituitary gland and have actions on many organs and tissues. Receptive cells possess particular receptors to which the peptides bind as ligands, leading to activation of G-protein-coupled receptors, hence cellular responses. In humans and other mammalian species, oxytocin and vasopressin mediate a range of peripheral and central physiological functions that are important for osmoregulation, reproduction, complex social behaviours, memory and learning. The origin of the oxytocin/vasopressin signalling system is thought to date back more than 600 million years. All vertebrate oxytocin- and vasopressin-like peptides have presumably evolved from the ancestral nonapeptide vasotocin by gene duplication and today are present in vertebrates, including mammals, birds, reptiles, amphibians and fish. Oxytocin- and vasopressin-like peptides have been identified in several invertebrate species, including molluscs, annelids, nematodes and arthropods. Members of this peptide family share high sequence similarity, and it is possible that they are functionally related across the entire animal kingdom. However, it is evident that not all animals express oxytocin/vasopressin neuropeptides and that there is little information available about the biology and physiology of this signalling system of invertebrates and, in particular, of insects, which represent more than half of all known living organisms. This report describes the discovery of novel oxytocin- and vasopressin-like peptides in arthropods and summarizes the status quo of the functional relevance of this neuropeptide signalling system in invertebrates, which will have beneficial implications for the design of selective and potent ligands to human oxytocin and vasopressin receptors.

The role of AMPK in controlling metabolism and mitochondrial biogenesis during exercise.

Abstract: New Findings What is the topic of this review? The topic of this review is the metabolic effects of AMP-activated protein kinase (AMPK) on glucose and fatty acid (FA) uptake, FA oxidation and mitochondrial biogenesis in skeletal muscle at rest and during exercise/muscle contractions. What advances does it highlight? This review describes recent studies examining the molecular mechanisms by which AMPK regulates muscle metabolism. It specifically discusses the role of exercise on acetyl-CoA carboxylase and malonyl-CoA in the regulation of FA oxidation. It also discusses the role of AMPK in regulating glucose and FA uptake during exercise. Finally, the review describes the interaction between AMPK, peroxisome proliferator-activated receptor γ co-activator-1α and sirtuin 1 in controlling mitochondrial biogenesis. Insulin resistance is associated with defects in skeletal muscle fatty acid (FA) metabolism that contribute to the development of type 2 diabetes. Endurance exercise increases FA and glucose metabolism, muscle mitochondrial content and insulin sensitivity. In skeletal muscle, basal rates of FA oxidation are dependent on AMP-activated protein kinase (AMPK) phosphorylation of acetyl-CoA carboxylase 2, the rate-limiting enzyme controlling the production of the metabolic intermediate malonyl-CoA. Likewise, AMPK is essential for maintaining muscle mitochondrial content in untrained mice; effects that may be mediated through regulation of the peroxisome proliferator-activated receptor γ co-activator-1α. However, the importance of AMPK in regulating glucose and FA uptake, FA oxidation and mitochondrial biogenesis during and following endurance exercise training is not fully understood. A better understanding of the mechanisms by which endurance exercise regulates substrate utilization and mitochondrial biogenesis may lead to improved therapeutic and preventative strategies for the treatment of insulin resistance and type 2 diabetes.

Regulation of the skeletal muscle blood flow in humans.

Abstract: In humans, skeletal muscle blood flow is regulated by an interaction between several locally formed vasodilators, including NO and prostaglandins. In plasma, ATP is a potent vasodilator that stimulates the formation of NO and prostaglandins and, very importantly, can offset local sympathetic vasoconstriction. Adenosine triphosphate is released into plasma from erythrocytes and endothelial cells, and the plasma concentration increases in both the feed artery and the vein draining the contracting skeletal muscle. Adenosine also stimulates the formation of NO and prostaglandins, but the plasma adenosine concentration does not increase during exercise. In the skeletal muscle interstitium, there is a marked increase in the concentration of ATP and adenosine, and this increase is tightly coupled to the increase in blood flow. The sources of interstitial ATP and adenosine are thought to be skeletal muscle cells and endothelial cells. In the interstitium, both ATP and adenosine stimulate the formation of NO and prostaglandins, but ATP has also been suggested to induce vasoconstriction and stimulate afferent nerves that signal to increase sympathetic nerve activity. Adenosine has been shown to contribute to exercise hyperaemia, whereas the role of ATP remains uncertain due to lack of specific purinergic receptor blockers for human use. The purpose of this review is to address the interaction between vasodilator systems and to discuss the multiple proposed roles of ATP in human skeletal muscle blood flow regulation.

Breath-by-breath pulmonary O2 uptake kinetics: effect of data processing on confidence in estimating model parameters

Abstract: To improve the signal-to-noise ratio of breath-by-breath pulmonary O2 uptake (VO2p) data, it is common practice to perform multiple step transitions, which are subsequently processed to yield an ensemble-averaged profile. The effect of different data-processing techniques on phase II VO2p kinetic parameter estimates (VO2p amplitude, time delay and phase II time constant (τVO2p)] and model confidence [95% confidence interval (CI95)] was examined. Young (n = 9) and older men (n = 9) performed four step transitions from a 20 W baseline to a work rate corresponding to 90% of their estimated lactate threshold on a cycle ergometer. Breath-by-breath VO2p was measured using mass spectrometry and volume turbine. Mono-exponential kinetic modelling of phase II VO2p data was performed on data processed using the following techniques: (A) raw data (trials time aligned, breaths of all trials combined and sorted in time); (B) raw data plus interpolation (trials time aligned, combined, sorted and linearly interpolated to second by second); (C) raw data plus interpolation plus 5 s bin averaged; (D) individual trial interpolation plus ensemble averaged [trials time aligned, linearly interpolated to second by second (technique 1; points joined by straight-line segments), ensemble averaged]; (E) 'D' plus 5 s bin averaged; (F) individual trial interpolation plus ensemble averaged [trials time aligned, linearly interpolated to second by second (technique 2; points copied until subsequent point appears), ensemble averaged]; and (G) 'F' plus 5 s bin averaged. All of the model parameters were unaffected by data-processing technique; however, the CI95 for τVO2p in condition 'D' (4 s) was lower (P < 0.05) than the CI95 reported for all other conditions (5-10 s). Data-processing technique had no effect on parameter estimates of the phase II VO2p response. However, the narrowest interval for CI95 occurred when individual trials were linearly interpolated and ensemble averaged.

Exercise performance is regulated during repeated sprints to limit the development of peripheral fatigue beyond a critical threshold.

Abstract: New Findings What is the central question of this study? We asked whether exercise performance is regulated during all-out repeated sprints (involving peak cycling-specific muscle activation and limited pacing strategy) in order to restrain the total degree of peripheral fatigue development. What is the main finding and its importance? Our results showed that power output is adjusted during repeated sprints to limit the development of peripheral fatigue to a critical threshold, independently of the degree of pre-existing fatigue. These findings emphasize the important role of peripheral fatigue in adjustment of power output during exercise. We hypothesized that exercise performance is adjusted during repeated sprints in order not to surpass a critical threshold of peripheral fatigue. Twelve men randomly performed three experimental sessions on different days, i.e. one single 10 s all-out sprint and two trials of 10 × 10 s all-out sprints with 30 s of passive recovery in between. One trial was performed in the unfatigued state (CTRL) and one following electrically induced quadriceps muscle fatigue (FTNMES). Peripheral fatigue was quantified by comparing pre- with postexercise changes in potentiated quadriceps twitch force (ΔQtw-pot) evoked by supramaximal magnetic stimulation of the femoral nerve. Central fatigue was estimated by comparing pre- with postexercise voluntary activation of quadriceps motor units. The root mean square (RMS) of the vastus lateralis and vastus medialis EMG normalized to maximal M-wave amplitude (RMS.Mmax−1) was also calculated during sprints. Compared with CTRL condition, pre-existing quadriceps muscle fatigue in FTNMES (ΔQtw-pot = −29 ± 4%) resulted in a significant (P < 0.05) reduction in power output (−4.0 ± 0.9%) associated with a reduction in RMS.Mmax−1. However, ΔQtw-pot postsprints decreased by 51% in both conditions, indicating that the level of peripheral fatigue was identical and independent of the degree of pre-existing fatigue. Our findings show that power output and cycling EMG are adjusted during exercise in order to limit the development of peripheral fatigue beyond a constant threshold. We hypothesize that the contribution of peripheral fatigue to exercise limitation involves a reduction in central motor drive in addition to the impairment in muscular function.

The paraventricular nucleus and heart failure.

Abstract: New Findings What is the topic of this review? This review gives an update on the cellular and molecular mechanisms within the autonomic nervous system involved in non-pathological and pathological cardiovascular regulation. What advances does it highlight? For cardiovascular homeostasis in non-pathological conditions to be maintained, discrete neural networks using specified signalling mechanisms at both cellular and molecular levels are required. In heart failure, the cell signalling protein partners CAPON and PIN decrease the bioavailability of nitric oxide by inhibiting neuronal nitric oxide synthase activity, leading to the removal of tonic neuronal inhibition. Following a myocardial infarction, pro-inflammatory cytokines in the paraventricular nucleus and the subsequent generation of reactive oxygen species, via angiotensin II activation of the angiotensin II type 1 receptor, increase neuronal excitability further, leading to sympathetic excitation. A pathological feature of heart failure is abnormal control of the sympathetic nervous system. The paraventricular nucleus of the hypothalamus (PVN) is one of the most important central sites involved in regulating sympathetic tone and is, in part, responsible for the dysregulation of the sympathetic nervous system evident in heart failure. Generation of sympathetic tone in response to fluctuations in cardiovascular regulation uses discrete anatomical pathways and neurochemical modulators. Direct and indirect projections from the PVN pre-autonomic neurons innervate the sympathetic preganglionic neurons in the spinal cord, which in turn innervate sympathetic ganglia that give rise to the sympathetic nerves. Pre-autonomic neurons of the PVN themselves receive an afferent input arising from the nucleus tractus solitarii, and viscerosensory receptors convey cardiovascular fluctuations to the nucleus tractus solitarii. The PVN contains excitatory and inhibitory neurons, whose balance determines the sympathetic tone. In non-pathological conditions, the tonic inhibition of the PVN pre-autonomic neurons is mediated by GABA- and NO-releasing neurons. In heart failure, the pre-autonomic neurons are disinhibited by the actions of the excitatory neurotransmitters glutamate and angiotensin II, leading to increased sympathetic activity. A key feature of the disinhibition is a reduction in the bioavailability of NO as a consequence of disrupted CAPON and PIN signalling mechanisms within the neuron. Another critical feature that contributes to increased neuronal excitation within the PVN is the production of pro-inflammatory cytokines immediately following a myocardial infarction, the activation of the angiotensin II type 1 receptor and the production of reactive oxygen species. By examining the changes associated with the sympathetic nervous system pathway, we will progress our understanding of sympathetic regulation in heart failure, identify gaps in our knowledge and suggest new therapeutic strategies.

Phox2b-expressing retrotrapezoid neurons and the integration of central and peripheral chemosensory control of breathing in conscious rats.

Abstract: New Findings What is the central question of this study? This study was designed to investigate whether the Phox2b-expressing neurons in the retrotrapezoid nucleus are important to breathing and chemoreflexes in conscious rats. What is the main finding and its importance? The high rate of destruction of a defined cell population (Phox2b+TH−) of the retrotrapezoid nucleus by the toxin suggests that the specialized connectivity of retrotrapezoid nucleus neurons, their glutamatergic nature and their relatively high sensitivity to CO2 are determinant factors in explaining their large contribution to the central and peripheral chemoreflexes. Chemoreception is the classic mechanism by which the brain regulates breathing in response to changes in tissue CO2/H+. A brainstem region called the retrotrapezoid nucleus (RTN) contains a population of Phox2b-expressing glutamatergic neurons that appear to function as important chemoreceptors. In the present study, we ask whether the destruction of a type of pH-sensitive interneuron that expresses the transcription factor Phox2b and is non-catecholaminergic (Phox2b+TH−) could affect breathing in conscious adult rats. The injection of substance P (1 nmol in a volume of 50 nl) into the RTN increased respiratory frequency, tidal volume, minute ventilation and mean arterial pressure. Bilateral injections of the toxin substance P conjugated with saporin (SSP–SAP) into the RTN destroyed Phox2b+TH− neurons but spared facial motoneurons, catecholaminergic and serotonergic neurons and the ventral respiratory column caudal to the facial motor nucleus. Bilateral inhibition of RTN neurons with SSP–SAP (0.6 ng in 30 nl) reduced resting ventilation and the increase in ventilation produced by hypercapnia (7% CO2) in conscious rats with or without peripheral chemoreceptors. In anaesthetized rats with bilateral lesions of around 90% of the Phox2b+TH− neurons, acute activation of the Botzinger complex, the pre-Botzinger complex or the rostral ventral respiratory group with NMDA (5 pmol in 50 nl) elicited normal cardiorespiratory output. In conclusion, the destruction of the Phox2b+TH− neurons is a plausible cause of the respiratory deficits observed after injection of SSP–SAP into the RTN. Our results also suggest that RTN neurons activate facilitatory mechanisms important to the control of breathing in resting or hypercapnic conditions in conscious adult rats.

Integrative physiological and computational approaches to understand autonomic control of cerebral autoregulation.

Abstract: The brain requires steady delivery of oxygen and glucose, without which neurodegeneration occurs within minutes. Thus, the ability of the cerebral vasculature to maintain relatively steady blood flow in the face of changing systemic pressure, i.e. cerebral autoregulation, is critical to neurophysiological health. Although the study of autoregulation dates to the early 20th century, only the recent availability of cerebral blood flow measures with high temporal resolution has allowed rapid, beat-by-beat measurements to explore the characteristics and mechanisms of autoregulation. These explorations have been further enhanced by the ability to apply sophisticated computational approaches that exploit the large amounts of data that can be acquired. These advances have led to unique insights. For example, recent studies have revealed characteristic time scales wherein cerebral autoregulation is most active, as well as specific regions wherein autonomic mechanisms are prepotent. However, given that effective cerebral autoregulation against pressure fluctuations results in relatively unchanging flow despite changing pressure, estimating the pressure-flow relationship can be limited by the error inherent in computational models of autoregulatory function. This review focuses on the autonomic neural control of the cerebral vasculature in health and disease from an integrative physiological perspective. It also provides a critical overview of the current analytical approaches to understand cerebral autoregulation.

Influence of locomotor muscle afferent inhibition on the ventilatory response to exercise in heart failure.

Abstract: New Findings What is the central question of this study? Patients with heart failure often develop ventilatory abnormalities at rest and during exercise, but the mechanisms underlying these abnormalities remain unclear. This study investigated the influence of inhibiting afferent neural feedback from locomotor muscles on the ventilatory response during exercise in heart failure patients. What is the main finding and its importance? Our results suggest that inhibiting afferent feedback from locomotor muscle via intrathecal opioid administration significantly reduces the ventilatory response to exercise in heart failure patients. Patients with heart failure (HF) develop ventilatory abnormalities at rest and during exercise, but the mechanism(s) underlying these abnormalities remain unclear. We examined whether the inhibition of afferent neural feedback from locomotor muscles during exercise reduces exercise ventilation in HF patients. In a randomized, placebo-controlled design, nine HF patients (age, 60 ± 2 years; ejection fraction, 27 ± 2%; New York Heart Association class 2 ± 1) and nine control subjects (age, 63 ± 2 years) underwent constant-work submaximal cycling (65% peak power) with intrathecal fentanyl (impairing the cephalad projection of opioid receptor-sensitive afferents) or sham injection. The hypercapnic ventilatory response was measured to determine whether cephalad migration of fentanyl occurred. There were no differences in hypercapnic ventilatory response within or between groups in either condition. Despite a lack of change in ventilation, tidal volume or respiratory rate, HF patients had a mild increase in arterial carbon dioxide () and a decrease in oxygen (; P < 0.05 for both) at rest. The control subjects demonstrated no change in , , ventilation, tidal volume or respiratory rate at rest. In response to fentanyl during exercise, HF patients had a reduction in ventilation (63 ± 6 versus 44 ± 3 l min−1, P < 0.05) due to a lower respiratory rate (30 ± 1 versus 26 ± 2 breaths min−1, P < 0.05). The reduced ventilation resulted in lower (97.6 ± 2.5 versus 79.5 ± 3.0 mmHg, P < 0.05) and increased (37.3 ± 0.9 versus 43.5 ± 1.1 mmHg, P < 0.05), with significant improvement in ventilatory efficiency (reduction in the ventilatory equivalent for carbon dioxide; P < 0.05 for all). The control subjects had no change in ventilation or measures of arterial blood gases. These data suggest that inhibition of afferent feedback from locomotor muscle significantly reduces the ventilatory response to exercise in HF patients.

Physiological mechanisms of sex differences in exertional dyspnoea: role of neural respiratory motor drive.

Abstract: New Findings What is the central question of this study? Does the combination of a higher neural respiratory drive and greater dynamic mechanical ventilatory constraints during exercise in healthy women versus men form the mechanistic basis of sex differences in activity-related dyspnoea? What is the main finding and its importance? Sex differences in activity-related dyspnoea in health primarily reflected the awareness of a higher neural respiratory drive needed to achieve any given ventilation during exercise in the setting of relatively greater dynamic mechanical ventilatory constraints in women. These findings may have implications for our understanding of the mechanisms of sex differences in exertional dyspnoea in variants of health (e.g. the elderly) and in patients with cardiorespiratory disease. The purpose of this study was to elucidate the physiological mechanisms of sex differences in exertional dyspnoea. We compared detailed measures of neural respiratory motor drive [diaphragmatic EMG (EMGdi) expressed as a percentage of maximal EMGdi (EMGdi%max)], breathing pattern, operating lung volumes, dynamic respiratory mechanics [tidal oesophageal (Poes,tidal%peak) and transdiaphragmatic pressure swings (Pdi,tidal%peak) expressed as a percentage of their respective peak values] and sensory intensity and unpleasantness ratings of dyspnoea during symptom-limited incremental cycle exercise in healthy young women (n = 25) and men (n = 25). The tidal volume to forced vital capacity ratio (VT%FVC), breathing frequency, EMGdi%max, Poes,tidal%peak, Pdi,tidal%peak and sensory intensity and unpleasantness ratings of dyspnoea were higher, while dynamic inspiratory capacity and inspiratory reserve volume were lower at a standardized absolute ventilation of 55 l min−1 during submaximal exercise in women versus men (all P < 0.05). In contrast, sex had no demonstrable effect on the inter-relationships between exercise-induced increases in VT%FVC, EMGdi%max and sensory intensity and unpleasantness ratings of dyspnoea. The results of this study suggest that sex differences in the intensity and unpleasantness of exertional dyspnoea in health are likely to reflect the awareness of a relatively higher neural respiratory motor drive (or EMGdi%max) needed to achieve any given ventilation during exercise in the setting of relatively greater dynamic mechanical constraints on VT expansion in women.

Assessment of dynamic cerebral autoregulation and cerebrovascular CO2 reactivity in ageing by measurements of cerebral blood flow and cortical oxygenation.

Abstract: New Findings What is the central question in this study? It is unknown to what extent increasing age influences the dynamic adaptations of cerebral blood flow velocity and cortical oxygenation in response to changes in blood pressure (cerebral autoregulation) and to changes in carbon dioxide (cerebrovascular CO2 reactivity). What is the main finding and its importance? We have shown that ageing up to 86 years is associated with an overall preservation of dynamic cerebral autoregulation and cerebrovascular CO2 reactivity, leading to a sufficiency of cerebral cortical oxygenation during daily life activities, despite the decrease in absolute cerebral blood flow velocity and increase in cerebrovascular resistance with advancing age. With ageing, cerebral blood flow velocity (CBFV) decreases; however, to what extent dynamic cerebral autoregulation and cerebrovascular CO2 reactivity are influenced by ageing is unknown. The aim was to examine the dynamic responses of CBFV and cortical oxygenation to changes in blood pressure (BP) and arterial CO2 across different ages. Fifty-eight participants in three age groups were included, as follows: young (n = 20, 24 ± 2 years old), elderly (n = 20, 66 ± 1 years old), and older elderly (n = 18, 78 ± 3 years old). The CBFV was measured using transcranial Doppler ultrasound, simultaneously with oxyhaemoglobin (O2Hb) using near-infrared spectroscopy and beat-to-beat BP measurements using Finapres. Postural manoeuvres were performed to induce haemodynamic fluctuations. Cerebrovascular CO2 reactivity was tested with hyperventilation and CO2 inhalation. With age, CBFV decreased (young 59 ± 12 cm s−1, elderly 48 ± 7 cm s−1 and older elderly 42 ± 9 cm s−1, P < 0.05) and cerebrovascular resistance increased (1.46 ± 0.58, 1.81 ± 0.36 and 1.98 ± 0.52 mmHg cm−1 s−1, respectively, P < 0.05). Normalized gain (autoregulatory damping) increased with age for BP–CBFV (0.88 ± 0.18, 1.31 ± 0.30 and 1.06 ± 0.34, respectively, P < 0.05) and CBFV–O2Hb (0.10 ± 0.09, 0.12 ± 0.04 and 0.17 ± 0.08, respectively, P < 0.05) during the repeated sit–stand manoeuvre at 0.05 Hz. Even though the absolute changes in CBFV and cerebrovascular resistance index during the cerebrovascular CO2 reactivity were higher in the young group, the percentage changes in CBFV, cerebrovascular resistance index and O2Hb were similar in all age groups. In conclusion, there was no decline in dynamic cerebral autoregulation and cerebrovascular CO2 reactivity with increasing age up to 86 years. Despite the decrease in cerebral blood flow velocity and increase in cerebrovascular resistance with advancing age, CBFV and cortical oxygenation were not compromised in these elderly humans during manoeuvres that mimic daily life activities.

Pathophysiology of human heart failure: importance of skeletal muscle myopathy and reflexes.

Abstract: In the last 20 years there has been mounting evidence that chronic heart failure (CHF) has a complex pathophysiology, which begins with an abnormality of the heart as a 'primum movens', but involves adaptive changes in many body parts, including the cardiovascular, musculoskeletal, renal, neuroendocrine, haemostatic, immune and inflammatory systems. Alterations in skeletal muscle are also of importance in limiting functional capacity in patients with CHF, because reduced physical activity plays some part in the muscle alterations in CHF. On the whole, these abnormalities resemble those induced by physical deconditioning. Moreover, the overactivation of signals originating from skeletal muscle receptors (mechano-metaboreceptors) is an intriguing hypothesis proposed to explain the origin of symptoms and the beneficial effect of exercise training in the CHF syndrome. These reflexes may contribute to sympathetic overactivation, to exercise intolerance and to the progression of CHF syndrome. The so-called metaboreflex has been reported to be hyperactive in CHF and to be responsible for a paradoxical increase in systemic vascular resistance and decrease in cardiac output whenever activated in these patients. This report is a brief summary of the latest news in this area of research.

Autonomic control of the heart during exercise in humans: role of skeletal muscle afferents.

Abstract: New findings What is the topic of this review? The autonomic nervous system plays a key role in bringing about the cardiovascular responses to exercise necessitated by the increased metabolic requirements of the active skeletal muscle. The complex interaction of central and peripheral neural control mechanisms evokes a decrease in parasympathetic activity and an increase sympathetic activity to the heart during exercise. What advances does it highlight? This review presents some of the recent insights provided by human studies into the role of mechanically and metabolically sensitive skeletal muscle afferents in the regulation of cardiac autonomic control during exercise. The autonomic responses to exercise are orchestrated by the interactions of several central and peripheral neural mechanisms. This report focuses on the role of peripheral feedback from skeletal muscle afferents in the autonomic control of the heart during exercise in humans. Heart rate responses to passive calf stretch are abolished with cardiac parasympathetic blockade, indicating that the activation of mechanically sensitive skeletal muscle afferents (muscle mechanoreceptors) can inhibit cardiac parasympathetic activity and is likely to contribute to the increase in heart rate at the onset of exercise. Recent experiments show that the partial restriction of blood flow to the exercising skeletal muscles, to augment the activation of metabolically sensitive skeletal muscle afferents (muscle metaboreceptors) in humans, evokes an increase in heart rate that is attenuated with β1-adrenergic blockade, thus suggesting that this response is principally mediated via an increase in cardiac sympathetic activity. Heart rate remains at resting levels during isolated activation of muscle metaboreceptors with postexercise ischaemia following hand grip, unless cardiac parasympathetic activity is inhibited, whereupon a sympathetically mediated increase in heart rate is unmasked. During postexercise ischaemia following leg cycling exercise, heart rate appears to remain elevated due to withdrawal of parasympathetic tone and/or the activation of sympathetic activity to the heart. Although the importance of skeletal muscle afferent feedback to the autonomic control of the heart during exercise is incontrovertible, the complexity of cardiac sympathetic–parasympathetic interactions and the absence of direct intraneural recordings in humans mean that it remains incompletely understood.

AltitudeOmics: effect of ascent and acclimatization to 5260 m on regional cerebral oxygen delivery

Abstract: Cerebral hypoxaemia associated with rapid ascent to high altitude can be life threatening; yet, with proper acclimatization, cerebral function can be maintained well enough for humans to thrive. We investigated adjustments in global and regional cerebral oxygen delivery (DO2) as 21 healthy volunteers rapidly ascended and acclimatized to 5260 m. Ultrasound indices of cerebral blood flow in internal carotid and vertebral arteries were measured at sea level, upon arrival at 5260 m (ALT1; atmospheric pressure 409 mmHg) and after 16 days of acclimatization (ALT16). Cerebral DO2 was calculated as the product of arterial oxygen content and flow in each respective artery and summed to estimate global cerebral blood flow. Vascular resistances were calculated as the quotient of mean arterial pressure and respective flows. Global cerebral blood flow increased by ∼70% upon arrival at ALT1 (P < 0.001) and returned to sea-level values at ALT16 as a result of changes in cerebral vascular resistance. A reciprocal pattern in arterial oxygen content maintained global cerebral DO2 throughout acclimatization, although DO2 to the posterior cerebral circulation was increased by ∼25% at ALT1 (P = 0.032). We conclude that cerebral DO2 is well maintained upon acute exposure and acclimatization to hypoxia, particularly in the posterior and inferior regions of the brain associated with vital homeostatic functions. This tight regulation of cerebral DO2 was achieved through integrated adjustments in local vascular resistances to alter cerebral perfusion during both acute and chronic exposure to hypoxia.

Centrally administered angiotensin-(1–7) increases the survival of stroke-prone spontaneously hypertensive rats

Abstract: New Findings What is the central question of this study? Activation of angiotensin-converting enzyme 2, resulting in production of angiotensin-(1–7) and stimulation of its receptor, Mas, exerts beneficial actions in a number cardiovascular diseases, including ischaemic stroke. A potential beneficial role for angiotensin-(1–7) in haemorrhagic stroke has not previously been reported. What is the main finding and its importance? Central administration of angiotensin-(1–7) into stroke-prone spontaneously hypertensive rats, a model of haemorrhagic stroke, increases lifespan and improves the neurological status of these rats, as well as decreasing microglial numbers in the striatum (implying attenuation of cerebral inflammation). These actions of angiotensin-(1–7) have not previously been reported and identify this peptide as a potential new therapeutic target in haemorrhagic stroke. Angiotensin-(1–7) [Ang-(1–7)] exerts cerebroprotective effects in ischaemic stroke, and this action is associated with a blunting of intracerebral inflammatory processes and microglial activation. Given that intracerebral inflammation and microglial activation play key roles in the mechanism of injury and brain damage in both ischaemic and haemorrhagic stroke, we have investigated the potential beneficial actions of Ang-(1–7) in stroke-prone spontaneously hypertensive rats (spSHRs), an established animal model of hypertension-induced haemorrhagic stroke. Angiotensin-(1–7) was administered by continuous infusion via the intracerebroventricular route for 6 weeks into spSHRs fed a high-sodium (4%) diet, starting at 49 days of age. This treatment resulted in a significant increase in survival of the spSHRs. Median survival was 108 days in control, artificial cerebrospinal fluid-infused spSHRs and 154 days in Ang-(1–7)-treated spSHRs. This effect was partly reversed by intracerebroventricular infusion of the Mas receptor blocker, A779. This Ang-(1–7) treatment also decreased the number of haemorrhages in the striatum, improved neurological status (reduced lethargy), decreased the number of microglia in the striatum and tended to increase neuron survival at the same site. Importantly, infusions of Ang-(1–7) had no effect on kidney pathology, heart pathology, body weight, serum corticosterone levels or blood pressure. This study is the first to demonstrate the cerebroprotective actions of Ang-(1–7), including increased survival time, in spSHRs. As such, these data reveal a potential therapeutic target for haemorrhagic stroke.

Dissociation between blood pressure and heart rate response to hypoxia after bilateral carotid body removal in men with systolic heart failure

Abstract: New Findings What is the central question of this study? Carotid body denervation removes the ventilatory response to acute hypoxia, although haemodynamic responses to acute hypoxia after carotid body removal have not been described conclusively in humans. What is the main finding and its importance? Carotid body removal results in dissociation of heart rate and blood pressure responses to hypoxia in human subjects. While the heart rate response (tachycardia) is maintained, there is a significant attenuation of the blood pressure response (hypertension), which indicates the existence of different sensory afferent pathways in the haemodynamic response to hypoxia that has important clinical implications for this novel therapeutic modality. While the ventilatory response to hypoxia is known to be mediated by the carotid bodies, the origin of the haemodynamic alterations evoked by hypoxia is less certain. Bilateral carotid body removal (CBR) performed to treat congestive heart failure may serve as a model to improve our understanding of haemodynamic responses to hypoxia in humans. We studied six congestive heart failure patients before and 1 month after CBR [median (interquartile range): age, 58.5 (56–61) years old; and ejection fraction, 32 (25–34)%]. Peripheral chemosensitivity (hypoxic ventilatory response) was equated to the slope relating lowest oxygen saturation to highest minute ventilation following exposures to hypoxia. Likewise, systolic blood pressure (SBP), diastolic blood pressure (DBP) and heart rate (HR) slopes were calculated as slopes relating the lowest oxygen saturations to the highest SBP, DBP and HR responses. We found that CBR reduces the hypoxic ventilatory response (∆91%, P < 0.05), SBP (∆71%, P < 0.05) and DBP slopes (∆59%, P = 0.07). In contrast, the HR slope remained unchanged. The dissociation between the blood pressure and HR responses after CBR shows involvement of a different chemoreceptive site(s) maintaining the response to acute hypoxia. We conclude that carotid bodies are responsible for ventilatory and blood pressure responses, while the HR response might be mediated by the aortic bodies. The significant reduction of the blood pressure response to hypoxia after CBR suggests a decrease in sympathetic tone, which is of particular clinical relevance in congestive heart failure.

Central fatigue contributes to the greater reductions in explosive than maximal strength with high-intensity fatigue.

Abstract: New Findings What is the central question of this study? Repeated high-force contractions of skeletal muscle cause a decline in the force-generating capacity, referred to as muscle fatigue. The influence of fatigue on explosive strength and the associated contractile and neural mechanisms responsible is not known. What is the main finding and its importance? Fatigue exerts a more pronounced influence on explosive force production than on maximal voluntary force production. Contractile and neural mechanisms were considered responsible. The study aimed to assess the influence of fatigue induced by repeated high-force explosive contractions on explosive and maximal isometric strength of the human knee extensors and to examine the neural and contractile mechanisms for the expected decrement. Eleven healthy untrained males completed 10 sets of voluntary maximal explosive contractions (five times 3 s, interspersed with 2 s rest). Sets were separated by 5 s, during which supramaximal twitch and octet contractions [eight pulses at 300 Hz that elicit the contractile peak rate of force development (pRFD)] were evoked. Explosive force, at specific time points, and pRFD were assessed for voluntary and evoked efforts, expressed in absolute terms and normalized to maximal/peak force. Maximal voluntary contraction force (MVCF) and peak evoked forces were also determined. Surface EMG amplitude was measured from three superficial agonists and normalized to maximal compound action potential area. By set 10, explosive force (47–52%, P < 0.001) and MVCF (42%, P < 0.001) had declined markedly. Explosive force declined more rapidly than MVCF, with lower normalized explosive force at 50 ms (29%, P = 0.038) that resulted in reduced normalized explosive force from 0 to 150 ms (11–29%, P ≤ 0.038). Neural efficacy declined by 34%, whilst there was a 15–28% reduction in quadriceps EMG amplitude during voluntary efforts (all P ≤ 0.03). There was demonstrable contractile fatigue (pRFD: octet, 27%; twitch, 66%; both P < 0.001). Fatigue reduced normalized pRFD for the twitch (21%, P = 0.001) but not the octet (P = 0.803). Fatigue exerted a more rapid and pronounced effect on explosive force than on MVCF, particularly during the initial 50 ms of contraction, which may explain the greater incidence of injuries associated with fatigue. Both neural and contractile fatigue mechanisms appeared to contribute to impaired explosive voluntary performance.

Upregulation of a local renin-angiotensin system in the rat carotid body during chronic intermittent hypoxia.

Abstract: The carotid body (CB) plays an important role in the alteration of cardiorespiratory activity in chronic intermittent hypoxia (IH) associated with sleep-disordered breathing, which may be mediated by local expression of the renin-angiotensin system (RAS). We hypothesized a pathogenic role for IH-induced RAS expression in the CB. The CB expression of RAS components was examined in rats exposed to IH resembling a severe sleep-apnoeic condition for 7 days. In situ hybridization showed an elevated expression of angiotensinogen in the CB glomus cells in the hypoxic group when compared with the normoxic control group. Immunohistochemical studies and Western blot analysis revealed increases in the protein level of both angiotensinogen and angiotensin II type 1 (AT1) receptors in the hypoxic group, which were localized to the glomic clusters containing tyrosine hydroxylase. RT-PCR studies confirmed that levels of the mRNA expression of angiotensinogen, angiotensin-converting enzyme, AT1a and AT2 receptors were significantly increased in the CBs of the hypoxic rats. Functionally, the [Ca(2+)]i response to exogenous angiotensin II was enhanced in fura-2-loaded glomus cells dissociated from hypoxic rats when compared with those of the normoxic control animals. Pretreatment with losartan, but not PD123319, abolished the angiotensin II-induced [Ca(2+)]i response, suggesting an involvement of AT1 receptors. Moreover, daily treatment of the IH group of rats with losartan attenuated the levels of oxidative stress, gp91(phox) expression and macrophage infiltration in the CB. Collectively, the upregulated local RAS expression could play a pathogenic role in the augmented CB activity and local inflammation via AT1 receptor activation during IH conditions in patients with sleep-disordered breathing.

Fructose supplementation worsens the deleterious effects of short‐term high‐fat feeding on hepatic steatosis and lipid metabolism in adult rats

Abstract: New Findings What is the central question of this study? In humans, ‘Western-style’ diet is characterized by high levels of both saturated fats and fructose. Lipid oversupply to the liver typical of high-fat diets could be exacerbated by the coexistence of high levels of fat and fructose in the diet, thus accelerating the development of metabolic deregulation. What is the main finding and its importance? Short-term consumption of a Western diet, rich in saturated fats and fructose, is more conducive to the development of liver steatosis and deleterious to glucose homeostasis than a high-fat diet. This result points to the harmful effect of adding fructose to the usual Western, high-fat diet. The purpose of the present study was to examine the short-term effect of high-fat or high-fat–high-fructose feeding on hepatic lipid metabolism and mitochondrial function in adult sedentary rats. Adult male rats were fed a high-fat or high-fat–high-fructose diet for 2 weeks. Body and liver composition, hepatic steatosis, plasma lipid profile and hepatic insulin sensitivity, together with whole-body and hepatic de novo lipogenesis, were assessed. Hepatic mitochondrial mass, functionality, oxidative stress and antioxidant defense were also measured. Rats fed the high-fat–high-fructose diet exhibited significantly higher plasma triglycerides, non-esterified fatty acids, insulin and indexes of hepatic insulin resistance compared with rats fed a low-fat or a high-fat diet. Hepatic triglycerides and ceramide, as well as the degree of steatosis and necrosis, were significantly higher, while liver p-Akt was significantly lower, in rats fed high-fat–high-fructose diet than in rats fed high-fat diet. A significant increase in non-protein respiratory quotient and hepatic fatty acid synthase and stearoyl CoA desaturase activity was found in rats fed the high-fat–high-fructose diet compared with those fed the high-fat diet. Significantly lower mitochondrial oxidative capacity but significantly higher oxidative stress was found in rats fed high-fat and high-fat–high-fructose diets compared with rats fed low-fat diet, while mitochondrial mass significantly increased only in rats fed high-fat–high-fructose diet. In conclusion, short-term consumption of a Western diet, rich in saturated fats and fructose, is more conducive to the development of liver steatosis and deleterious to glucose homeostasis than a high-fat diet.

Diminished nitric oxide-dependent sweating in older males during intermittent exercise in the heat

Abstract: Nitric oxide (NO) is a signalling molecule that contributes to the control of many physiological pathways, including the heat-loss response of skin vasodilatation. Recently, NO has been implicated in the control of sweating during exercise in young adults. We tested the hypothesis that ageing reduces NO-dependent sweating during exercise in the heat. Ten young (23 ± 3 years old) and 10 older men (64 ± 5 years old), matched for body surface area, performed three successive 15 min bouts of exercise (Ex1, Ex2 and Ex3) at the same rate of metabolic heat production (300 W m(-2)) in the heat (35°C, 20% relative humidity). Exercise periods were interspersed with 15 min recovery periods. Local sweat rate (ventilated capsule) was measured on two forearm skin sites, which were continuously perfused via intradermal microdialysis with 0.9% saline as control (CON) or 10 mm N(G)-nitro-l-arginine methyl ester (L-NAME), a non-selective NO synthase inhibitor. Local sweat rate at the end of Ex1 was lower in the CON conditions in the older versus young men (0.69 ± 0.19 versus 0.90 ± 0.17 mg min(-1) cm(-2), P = 0.018). In the young men, local sweat rate was reduced in the L-NAME-treated conditions compared with the CON conditions at the end of Ex1 (0.67 ± 0.14 versus 0.90 ± 0.17 mg min(-1) cm(-2), P = 0.004), Ex2 (0.78 ± 0.20 versus 1.03 ± 0.20 mg min(-1) cm(-2), P = 0.013) and Ex3 (0.78 ± 0.20 versus 1.03 ± 0.21 mg min(-1) cm(-2), P = 0.014). In the older men, there was no main effect of treatment conditions on local sweat rate (P = 0.537) such that local sweat rates in the L-NAME-treated and CON conditions were similar (Ex1, 0.65 ± 0.20 versus 0.69 ± 0.19 mg min(-1) cm(-2); Ex2, 0.80 ± 0.27 versus 0.91 ± 0.29 mg min(-1) cm(-2); and Ex3, 0.84 ± 0.31 versus 0.94 ± 0.38 mg min(-1) cm(-2)). We conclude that ageing attenuates the influence of NO in the control of local forearm sweating observed in young adults during short 15 min bouts of exercise in the heat. This mechanism may, in part, explain the age-related impairments in sweating.

Introducing a rat model of prenatal androgen-induced polycystic ovary syndrome in adulthood

Abstract: New Findings What is the central question of this study? Would it be possible to produce a rat model of polycystic ovary syndrome (PCOS), in which the fetuses are exposed to testosterone for a short time and exhibit both endocrine and ovarian disturbances similar to PCOS, while maintaining normal reproductive system morphology in adulthood? What is the main finding and its importance? Prenatal exposure to a single dose of testosterone during the critical period of fetal development facilitates the production of a functional rat model of PCOS with minimal morphological disorders in adulthood. Production of a functional rat model that resembles many features of PCOS may contribute to a better understanding of this syndrome. Polycystic ovary syndrome (PCOS) is one of the most common endocrine disorders in women, with a prevalence of 8–12% during the reproductive years. In the present study, using prenatal exposure to a single dose of testosterone during the critical period of fetal development, we aimed to introduce an enhanced rat model that would exhibit both endocrine and ovarian disturbances similar to PCOS, while maintaining normal reproductive system morphology in adulthood. Ten pregnant rats were injected s.c. with 5 mg free testosterone on gestational day 20, while control rats received only solvent. The development and function of the reproductive system in female offspring were examined in adulthood. Prenatally androgenized offspring had irregular oestrous cycles compared with control animals, and their anogenital and anovaginal distances were increased compared with control rats (P < 0.001). No significant differences were observed in the lengths of the vagina and clitoris or the number of nipples between the two groups. Levels of testosterone and luteinizing hormone and the luteinizing hormone/follicle-stimulating hormone ratio were increased in prenatally androgenized offspring compared with control animals (P < 0.05). The numbers of preantral and antral follicles in the ovaries of prenatally androgenized offspring were also increased compared with control rats (P = 0.07 and P < 0.01, respectively). The number of corpora lutea was decreased in prenatally androgenized offspring compared with control rats. Cystic follicles were observed in the ovaries of prenatally androgenized offspring. Prenatal exposure to a single dose of testosterone during the critical period of fetal development could facilitate the development a functional rat model of PCOS in adulthood, with minimal morphological disorders in the reproductive system.