Showing papers in "Experimental Physiology in 2005"

Non-invasive pulsatile arterial pressure and stroke volume changes from the human finger

Abstract: In this paper we review recent developments in the methodology of non-invasive finger arterial pressure measurement and the information about arterial flow that can be obtained from it. Continuous measurement of finger pressure based on the volume-clamp method was introduced in the early 1980s both for research purposes and for clinical medicine. Finger pressure tracks intra-arterial pressure but the pressure waves may differ systematically both in shape and magnitude. Such bias can, at least partly, be circumvented by reconstruction of brachial pressure from finger pressure by using a general inverse anti-resonance model correcting for the difference in pressure waveforms and an individual forearm cuff calibration. The Modelflow method as implemented in the Finometer computes an aortic flow waveform from peripheral arterial pressure by simulating a non-linear three-element model of the aortic input impedance. The methodology tracks fast changes in stroke volume (SV) during various experimental protocols including postural stress and exercise. If absolute values are required, calibration against a gold standard is needed. Otherwise, Modelflow-measured SV is expressed as change from control with the same precision in tracking. Beat-to-beat information on arterial flow offers important and clinically relevant information on the circulation beyond what can be detected by arterial pressure.

Actions of TNF‐α on glutamatergic synaptic transmission in the central nervous system

Abstract: Increasing attention is being paid to the role of inflammatory and immune molecules in the modulation of central nervous system (CNS) function. Tumour necrosis factor-alpha (TNF-alpha) is a pro-inflammatory cytokine, the receptors for which are expressed on neurones and glial cells throughout the CNS. Through the action of its two receptors, it has a broad range of actions on neurones which may be either neuroprotective or neurotoxic. It plays a facilitatory role in glutamate excitotoxicity, both directly and indirectly by inhibiting glial glutamate transporters on astrocytes. Additionally, TNF-alpha has direct effects on glutamate transmission, for example increasing expression of AMPA receptors on synapses. TNF-alpha also plays a role in synaptic plasticity, inhibiting long-term potentiation (LTP), a process dependent on p38 mitogen activated kinase (p38 MAP) kinase. In the following review we look at these and other effects of TNF-alpha in the CNS.

Crossing the apnoeic threshold: causes and consequences.

Abstract: This brief review addresses the characteristics, lability and the mechanisms underlying the hypocapnic-induced apnoeic threshold which is unmasked during NREM sleep. The role of carotid chemoreceptors as fast, sensitive detectors of dynamic changes in CO2 is emphasized and placed in historical context of the long-held debate over central vs. peripheral contributions to CO2 sensing and to apnoea. Finally, evidence is presented which points to a significant role for unstable, central respiratory motor output as a significant contributor to upper airway narrowing and obstruction during sleep.

Intracellular mechanisms involved in vascular remodelling of resistance arteries in hypertension: role of angiotensin II.

Abstract: Resistance arteries undergo structural changes (vascular remodelling) in hypertension These changes involve media thickening, reduced lumen diameter and consequent increased media:lumen ratio Cellular processes underlying these events include altered vascular smooth muscle cell (VSMC) growth, migration, differentiation and increased extracellular matrix abundance Another factor contributing to remodelling is inflammation, associated with macrophage infiltration, fibrosis and increased expression of redox-sensitive pro-inflammatory genes Among the factors involved in arterial remodelling, angiotensin (Ang) II appears to be one of the most important Ang II, a multifunctional peptide with pleiotropic actions, modulates vasomotor tone, cell growth, apoptosis/anoikis, cell migration and extracellular matrix deposition It is pro-inflammatory and it stimulates production of growth factors and vasoactive agents The multiple actions of Ang II are mediated via complex intracellular signalling pathways including stimulation of the phosholipase C (PLC)-inositol 1,4,5-trisphosphate (IP3)-1,2-diacylglycerol (DAG) cascade, mitogen-activated protein (MAP) kinases, tyrosine kinases and RhoA/Rho kinase Furthermore, Ang II elicits many of its (patho)physiological effects by stimulating reactive oxygen species (*O2- and H2O2) generation through activation of vascular NAD(P)H oxidase *O2- and H2O2 in turn influence downstream signalling molecules including transcription factors, tyrosine kinases/phosphatases, Ca2+ channels and MAP kinases Interaction between these systems is complex and dysregulation at any level may contribute to vascular remodelling Targeting such molecules/pathways could prevent or induce regression of hypertensive vascular damage thereby ameliorating development of hypertension and preventing target organ damage The present review discusses the role of Ang II in remodelling of resistance arteries, focusing on some signalling pathways involved in vascular growth and inflammation in hypertension

Protection from angiotensin II-induced cardiac hypertrophy and fibrosis by systemic lentiviral delivery of ACE2 in rats.

Abstract: Angiotensin converting enzyme 2 (ACE2), a newly discovered member of the renin-angiotensin system (RAS), is a potential therapeutic target for the control of cardiovascular disease owing to its key role in the formation of vasoprotective peptides from angiotensin II. The aim of the present study was to evaluate whether overexpression of ACE2 could protect the heart from angiotensin II-induced hypertrophy and fibrosis. Lentiviral vector encoding mouse ACE2 (lenti-mACE2) or GFP was injected intracardially in 5-day-old Sprague-Dawley rats. This resulted in expression of mACE2 in cardiac tissue for the duration of the study. Infusion of 200 ng kg-1 min-1 angiotensin II for 4 weeks resulted in an 80 mmHg increase in systolic blood pressure, a significant increase in the heart weight to body weight ratio (HW:BW), and marked myocardial fibrosis in control rats. Transduction with lenti-mACE2 resulted in significant attenuation of the increased HW:BW and myocardial fibrosis induced by angiotensin II infusion. These observations demonstrate that ACE2 overexpression results in protective effects on angiotensin II-induced cardiac hypertrophy and fibrosis.

Promoters and serotypes: targeting of adeno-associated virus vectors for gene transfer in the rat central nervous system in vitro and in vivo.

Abstract: The brain parenchyma consists of several different cell types, such as neurones, astrocytes, microglia, oligodendroglia and epithelial cells, which are morphologically and functionally intermingled in highly complex three-dimensional structures. These different cell types are also present in cultures of brain cells prepared to serve as model systems of CNS physiology. Gene transfer, either in a therapeutic attempt or in basic research, is a fascinating and promising tool to manipulate both the complex physiology of the brain and that of isolated neuronal cells. Viral vectors based on the parvovirus, adeno-associated virus (AAV), have emerged as powerful transgene delivery vehicles. Here we describe highly efficient targeting of AAV vectors to either neurones or astrocytes in cultured primary brain cell cultures. We also show that transcriptional targeting can be achieved by the use of small promoters, significantly boosting the transgene capacity of the recombinant viral genome. However, we also demonstrate that successful targeting of a vector in vitro does not necessarily imply that the same targeting works in the adult brain. Cross-packaging the AAV-2 genome in capsids of other serotypes adds additional benefits to this vector system. In the brain, the serotype-5 capsid allows for drastically increased spread of the recombinant vector as compared to the serotype-2 capsid. Finally, we emphasize the optimal targeting approach, in which the natural tropism of a vector for a specific cell type is employed. Taken together, these data demonstrate the flexibility which AAV-based vector systems offer in physiological research.

A role for the paraventricular nucleus of the hypothalamus in the autonomic control of heart and kidney

Abstract: It is now well accepted that the sympathetic nervous system responds to specific afferent stimuli in a unique non-uniform fashion. The means by which the brain transforms the signals from a single type of receptor into an appropriate differential sympathetic output is discussed in this brief review. The detection of and response to venous filling are used for illustration. An expansion of blood volume has been shown in a number of species to increase heart rate reflexly via sympathetic nerves and this effect is primarily an action of volume receptors at the venous-atrial junctions of the heart. Stimulation of these volume receptors also leads to an inhibition of renal sympathetic nerve activity. Thus the reflex response to an increase in plasma volume consists of a distinctive unique pattern of sympathetic activity to maintain fluid balance. This reflex is dependent on neurones in the paraventricular nucleus (PVN). Neurones in the PVN show early gene activation on stimulation of atrial receptors, and a similar differential pattern of cardiac sympathetic excitation and renal inhibition can be evoked by activating PVN neurones. Cardiac atrial afferents selectively cause a PVN GABA neurone-induced inhibition within the PVN of PVN spinally projecting vasopressin-containing neurones that project to renal sympathetic neurones. A lesion of these spinally projecting neurones abolishes the reflex. With regard to the cardiac sympathetics, there is a population of PVN spinally projecting neurones that selectively increase heart rate by the release of oxytocin, a peptide pathway that has no action on renal sympathetic outflow. In heart failure the atrial reflex becomes blunted, and evidence is emerging that there is a downregulation of nitric oxide synthesis and reduced GABA activity in the PVN. How this might give rise to increased sympathetic activity associated with heart failure is briefly discussed.

Therapeutic Angiogenesis and Vasculogenesis for Tissue Regeneration

Abstract: Therapeutic angiogenesis/vasculogenesis holds promise for the cure of ischaemic disease. The approach postulates the manipulation of spontaneous healing response by supplementation of growth factors or transplantation of vascular progenitor cells. These supplements are intended to foster the formation of arterial collaterals and promote the regeneration of damaged tissues. Angiogenic factors are generally delivered in the form of recombinant proteins or by gene transfer using viral vectors. In addition, new non-viral methods are gaining importance for their safer profile. The association of growth factors with different biological activity might offer distinct advantages in terms of efficacy, yet combined approaches require further optimization. Alternatively, substances with pleiotropic activity might be considered, by virtue of their ability to target multiple mechanisms. For instance, some angiogenic factors not only stimulate the growth of arterioles and capillaries, but also inhibit vascular destabilization triggered by metabolic and oxidative stress. Transplantation of endothelial progenitor cells was recently proposed for the treatment of peripheral and myocardial ischaemia. Progenitor cells can be transplanted either without any preliminary conditioning or after ex vivo genetic manipulation. Delivery of genetically modified progenitor cells eliminates the drawback of immune response against viral vectors and makes feasible repeating the therapeutic procedure in case of injury recurrence. It is envisioned that these new approaches of regenerative medicine will open unprecedented opportunities for the care of life-threatening diseases.

Hypoxia‐inducible factor as a physiological regulator

Abstract: Hypoxia-inducible factor (HIF) is a transcription complex which responds to changes in oxygen, providing cells with a master regulator that coordinates changes in gene transcription. HIF operates in all mammalian cell types and is ancient in evolutionary terms, being conserved in C. elegans and D. melanogaster. This review summarizes recent insights into the molecular events that link reduced oxygenation to HIF activation and emerging insights into the extensive role of HIF in a broad range of physiological processes.

Oxidative stress and vascular remodelling.

Abstract: Oxidative stress plays an important role in the pathophysiology of vascular diseases. Reactive oxygen species, especially superoxide anion and hydrogen peroxide, are important signalling molecules in cardiovascular cells. Enhanced superoxide production increases nitric oxide inactivation and leads to an accumulation of peroxynitrites and hydrogen peroxide. Reactive oxygen species participate in growth, apoptosis and migration of vascular smooth muscle cells, in the modulation of endothelial function, including endothelium-dependent relaxation and expression of proinflammatory phenotype, and in the modification of the extracellular matrix. All these events play important roles in vascular diseases such as hypertension, suggesting that the sources of reactive oxygen species and the signalling pathways that they modify may represent important therapeutic targets. Potential sources of vascular superoxide production include NADPH-dependent oxidases, xanthine oxidases, lipoxygenases, mitochondrial oxidases and nitric oxide synthases. Studies performed during the last decade have shown that NADPH oxidase is the most important source of superoxide anion in phagocytic and vascular cells. Evidence from experimental animal and human studies suggests a significant role of NADPH oxidase activation in the vascular remodelling and endothelial dysfunction found in cardiovascular diseases.

Effect of whole body resistance training on arterial compliance in young men.

Abstract: The effect of resistance training on arterial stiffening is controversial. We tested the hypothesis that resistance training would not alter central arterial compliance. Young healthy men (age, 23 +/- 3.9 (mean +/- s.e.m.) years; n = 28,) were whole-body resistance trained five times a week for 12 weeks, using a rotating 3-day split-body routine. Resting brachial blood pressure (BP), carotid pulse pressure, carotid cross-sectional compliance (CSC), carotid initima-media thickness (IMT) and left ventricular dimensions were evaluated before beginning exercise (PRE), after 6 weeks of exercise (MID) and at the end of 12 weeks of exercise (POST). CSC was measured using the pressure-sonography method. Results indicate reductions in brachial (61.1 +/- 1.4 versus 57.6 +/- 1.2 mmHg; P < 0.01) and carotid pulse pressure (52.2 +/- 1.9 versus 46.8 +/- 2.0 mmHg; P < 0.01) PRE to POST. In contrast, carotid CSC, beta-stiffness index, IMT and cardiac dimensions were unchanged. In young men, central arterial compliance is unaltered with 12 weeks of resistance training and the mechanisms responsible for cardiac hypertrophy and reduced arterial compliance are either not inherent to all resistance-training programmes or may require a prolonged stimulus.

Role of leptin in obesity-related hypertension.

Abstract: Obesity in humans causes hypertension, myocardial hypertrophy and coronary atherosclerosis, and increased cardiovascular morbidity and mortality that is thought to be related to sympathetic overactivity Leptin is an adipocyte-derived hormone that acts in the hypothalamus to regulate appetite, energy expenditure and sympathetic nervous system outflow One of the major mechanisms leading to the development of obesity-induced hypertension appears to be leptin-mediated sympatho-activation Leptin adversely shifts the renal pressure-natriuresis curve, leading to relative sodium retention Although obesity is generally associated with resistance to the anorexic and weight-reducing actions of leptin, our work has shown preservation of its sympatho-excitatory and pressor actions This selective leptin resistance of obesity, coupled with hyperleptinaemia, may play a critical role in the cardiovascular complications of obesity Increased information about leptin and its mechanisms of actions should help the development of safe and effective pharmacological treatments of obesity and obesity-related hypertension

Vagal control of the heart: central serotonergic (5‐HT) mechanisms

Abstract: Cardiac vagal preganglionic neurones (CVPNs) are located within the dorsal vagal nucleus (DVN) and the nucleus ambiguus (nA). In mammals, CVPNs within the nA have small myelinated axons and mediate major chronotropic effects, those in the DVN have non-myelinated axons and mediate smaller chronotropic, dromotropic and inotropic effects. Numerous studies demonstrate important influences of serotonin (5-HT) at multiple sites controlling autonomic outflows including the nucleus tractus solitarius (NTS) where cardiorespiratory afferent fibres terminate, and the CVPNs and rostral ventrolateral medulla (RVLM), the location of sympathetic premotor neurones. We have demonstrated roles for some of the numerous 5-HT receptor subtypes (5-HT1, 5-HT2, 5-HT3, 5-HT4 and 5-HT7) in brainstem regions involved in cardiac control. Intracisternal application of selective ligands was used to study the effect of 5-HT receptors on heart rate and its reflex control. Further electrophysiological studies were also carried out to delineate their location and the mechanisms of action of these ligands. Blocking 5-HT1A receptors attenuated bradycardias evoked by stimulating baroreceptor and cardiopulmonary afferents but not arterial chemoreceptors, whereas antagonizing 5-HT7 receptors markedly attenuated all these reflex bradycardias. Within the DVN, nA and NTS, activation of 5-HT1A receptors could excite or inhibit neurones. In the NTS 5-HT2 receptors also had variable effects; 5-HT2B receptors excite and 5-HT2C receptors inhibit. Antagonism of 5-HT3 receptors attenuated upper airway and cardiopulmonary reflex bradycardias; this is compatible with data showing that 5-HT3 receptors excite DVN and NTS neurones by a glutamate-dependent mechanism. The origin of the glutamate (neuronal or glial) remains unresolved but glia are a possibility as barorecptor-sensitive NTS neurones receive few direct 5-HT-containing synaptic contacts. Thus, 5-HT plays a critical role in the control of vagal outflow to the heart; however, why so many different receptors are involved, and their relative functional roles, remains unresolved.

Homing in on the specific phenotype(s) of central respiratory chemoreceptors.

Abstract: To some it may seem that we now know less about respiratory chemoreception than we did 20 years ago. Back then, it was widely accepted that the central respiratory chemoreceptors (CRCs) were located exclusively on or near the surface of the ventrolateral medulla (VLMS). Now, instead, it is generally believed that there are widespread sites of chemoreception, and there is little agreement on when and how each of these sites is involved in respiratory control. However, those in the field know that this actually is progress, primarily because we have gone from simply identifying candidate regions, to identifying specific neuronal subtypes that may be the sensors. In this invited review, we have been asked to discuss some of the current controversies in the field. First, we define the minimal requirements for a cell to be a CRC, and what assumptions can not be made without more data. Then we review the evidence that two neuronal subtypes, serotonergic neurones of the midline raphe and glutamatergic neurones of the retrotrapezoid nucleus, are chemoreceptors. There is evidence supporting a role in respiratory chemoreception for both types of neurone, as well as the other candidates, but there is also information that is missing. Future work will need to focus on which of the candidates are indeed chemoreceptors, what percentage of the overall response each one contributes, and how this percentage varies under different conditions.

Short-term effects of streptozotocin-induced diabetes on the electrocardiogram, physical activity and body temperature in rats.

Abstract: A variety of contractility defects have been reported in the streptozotocin (STZ)-induced diabetic rat heart including alterations to the amplitude and time course of cardiac muscle contraction. Transmitter devices were surgically implanted in the peritoneal cavity of young adult male Wistar rats. Electrodes from the transmitter were arranged in Einthoven bipolar lead II configuration. Electrocardiogram (ECG), physical activity and body temperature data were continuously recorded with a telemetry system before and following the administration of STZ (60 mg kg-1). Heart rate (HR), physical activity and body temperature declined rapidly 3-5 days after administration of STZ. The effects became more conspicuous with time and reached a new steady state approximately 10 days after STZ treatment when HR was 255+/-8 beats min-1 in diabetic rats compared to 348+/-17 beats min-1 in age-matched controls. Heart rate variability (HRV) was also significantly reduced after STZ treatment (18+/-3 beats min-1) compared to controls (36+/-3 beats min-1). Reduced physical activity and/or body temperature may partly underlie the reduction in HR and HRV. Reductions in power spectral density at higher frequencies (2.5-3.5 Hz) suggest that parasympathetic drive to the heart may be altered during the early stages of STZ-induced diabetes. Short-term diabetes-induced changes in vital signs can be effectively tracked by continuous recording using a telemetry system.

High intensity exercise increases expression of matrix metalloproteinases in fast skeletal muscle fibres

Abstract: Metalloproteinases (MMPs) are proteolytic enzymes that function in the extracellular matrix to degrade connective tissues. While it is clear that exercise-induced injury in skeletal muscle promotes increased expression of MMPs, the relationship between exercise intensity and expression of MMPs in muscles is unknown. These experiments tested the hypothesis that exercise-induced expression of matrix metalloproteinases (MMP-2 and MMP-9) is dose-dependent such that high-intensity endurance exercise increases MMP expression whereas low-intensity endurance exercise will not promote MMP expression in skeletal muscles. Female rats (4 months old) completed 2 weeks of treadmill running at either low (18 m min(-1); approximately 50% maximum oxygen consumption rate ) or high intensity (32 m min(-1); approximately 70% ; up to 50 min day(-1)). Non-running, sedentary animals served as controls. Muscle mRNA and protein levels of MMP-2 and MMP-9 were assessed in gastrocnemius, quadriceps and soleus muscles by reverse transcriptase-polymerase chain reaction and Western blotting, respectively. Results indicate that exercise did not alter MMP-9 in any of these skeletal muscles. Further, our data reveal that low-intensity exercise did not alter the expression of MMP-2 in any of the muscles investigated. In contrast, high-intensity exercise increased both mRNA and protein levels of MMP-2 in skeletal muscles containing a high percentage of fast type II fibres (i.e. gastronemius and superficial quadriceps). These results support the hypothesis that high-intensity exercise is required to promote the expression of MMP-2 in skeletal muscles and that the influence of exercise on MMP-2 expression is dominant in muscles containing a high percentage of fast fibres.

Retrotrapezoid nucleus: a litmus test for the identification of central chemoreceptors.

Abstract: Central chemoreception is the mechanism by which arterial blood P C O 2 is detected by the CNS to regulate breathing. Two main theories have been proposed to account for the phenomenon. The distributed chemosensitivity theory argues that pH sensitivity is a widespread attribute of brainstem neurones and that central chemoreception results from the cumulative effects of pH on countless neurones. The specialized chemoreceptor theory envisions the existence of small and specialized populations of CNS cells (chemoreceptors) that are unique in their ability to detect very small pH fluctuations and, via specific connections, regulate a respiratory network that is itself unresponsive to pH. The recently identified CO 2 -sensitive neurones of the retrotrapezoid nucleus (RTN) seem to possess most of the attributes that one would expect of such chemoreceptors. In this review we also suggest that many fewer medullary neurones are intrinsically responsive to CO 2 in vivo than might have been anticipated from prior experimentation in vitro. The properties of RTN neurones provide renewed support for the specialized chemoreceptor theory of central chemoreception, proposed in the early 1960s. However, many uncertainties remain, especially as regards the molecular mechanisms of chemoreception, the type of cell that actually detects pH in vivo (neurone, glia or others) and the number and location of bonafide central chemoreceptors.

Kallikrein-kinin in stroke, cardiovascular and renal disease.

Abstract: Tissue kallikrein, a serine proteinase, produces the potent vasodilator kinin peptide from kininogen substrate. The levels of tissue kallikrein are reduced in humans and animal models with hypertension, cardiovascular and renal disease. Using transgenic and somatic gene transfer approaches, we investigated the role of the tissue kallikrein-kinin system in cardiovascular, renal and central nervous systems. A single injection of the human tissue kallikrein gene in plasmid DNA or an adenoviral vector resulted in a prolonged reduction of blood pressure and attenuation of hypertrophy and fibrosis in the heart and kidney of several hypertensive animal models. Furthermore, enhanced kallikrein-kinin levels after gene transfer exerted beneficial effects, with protection against cardiac remodelling, renal injuries, restenosis, cerebral infarction and neurological deficits in normotensive animal models without haemodynamic effects, indicating direct actions of kallikrein independent of its ability to lower blood pressure. The effects of kallikrein were mediated by the kinin B2 receptor, as the specific B2 receptor antagonist icatibant abolished the actions of kallikrein. Moreover, kallikrein-kinin exhibited pleiotropic effects by inhibiting apoptosis, inflammation, hypertrophy and fibrosis, and promoting angiogenesis and neurogenesis in the heart, kidney, brain and blood vessel. Exogenous administration of kallikrein also led to increased nitric oxide (NO)/cGMP and cAMP levels, and reduced NAD(P)H oxidase activities, superoxide formation and pro-inflammatory cytokine levels. These results indicate a novel role of kallikrein-kinin through the kinin B2 receptor as an antioxidant and anti-inflammatory agent in protection against stroke, cardiovascular and renal disease, and may uncover new drug targets for the prevention and treatment of heart failure, vascular injury, end-stage renal disease and stroke in humans.

Effects of co-supplementation of vitamins E and C on gentamicin-induced nephrotoxicity in rat.

Abstract: Gentamicin (GM) is an effective antibiotic against severe gram-negative infections. However it can produce nephrotoxicity in human. Reactive oxygen species (ROS) have been proposed as the causative factors of the renal side effects the drug. This study was performed to investigate the protective role of antioxidant vitamins against GM-mediated nephropathy in an in situ model of isolated rat kidney. Male Sprague-Dawley rats were randomly assigned to one of the following groups of seven rats: group 1 (Control) was perfused with Tyrode solution; group 2 (GM), 200 microg ml(-1) GM was added to the perfusate; group 3 (GM + Vit C), as group 2 with vitamin C added to the drinking water for 3 days (200 mg l(-1)) and to the perfusate (100 mg l(-1)); group 4 (GM + Vit E), as group 2 with vitamin E (100 mg (100 g body weight)(-1), i.m.) injected 12 h before the start of the experiment; group 5 (GM + Vit C + Vit E) as group 2 with vitamin E and C co-administered (concentrations and conditions as in groups 3 and 4). To compare the groups, urinary lactate dehydrogenase (LDH), N-acetyle-beta-D-glucosaminidase (NAG) and alkaline phosphatase (ALP) activities, inulin clearance (glomerular filtration rate, GFR) and renal tissue glutathione (GSH) content were measured. GM caused a significant nephrotoxicity demonstrated by an increase in urinary LDH, NAG and ALP activities. Reduction in GSH content and a marked decrease in GFR were observed compared to controls. Vitamin C inhibited the GM-induced increase in urinary enzyme activities but did not show a significant effect on the GSH content or GFR. Vitamin E prevented the GM-induced reduction in GSH level without a significant improvement in GFR. Co-administration of vitamins C and E significantly prevented the GM-induced nephrotoxicity demonstrating by preservation of GFR and GSH levels and prevention of increase in urinary enzyme activities. We conclude that co-administration of moderate doses of vitamins C and E has beneficial effects on renal preservation in GM-induced nephrotoxicity.

Re: Retrotrapezoid nucleus: a litmus test for the identification of central chemoreceptors

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New aspects of vascular remodelling: the involvement of all vascular cell types

Abstract: Conventionally, the architecture of arteries is based around the close-packed smooth muscle cells and extracellular matrix. However, the adventitia and endothelium are now viewed as key players in vascular growth and repair. A new dynamic picture has emerged of blood vessels in a constant state of self-maintenance. Recent work raises fundamental questions about the cellular heterogeneity of arteries and the time course and triggering of normal and pathological remodelling. A common denominator emerging in hypertensive remodelling is an early increase in adventitial cell density suggesting that adventitial cells drive remodelling and may initiate subsequent changes such as re-arrangement of smooth muscle cells and extracellular matrix. The organization of vascular smooth muscle cells follows regular arrangements that can be modelled mathematically. In hypertension, new patterns can be quantified in these terms and give insights to how structure affects function. As with smooth muscle, little is known about the organization of the vascular endothelium, or its role in vascular remodelling. Current observations suggest that there may be a close relationship between the helical organization of smooth muscle cells and the underlying pattern of endothelial cells. The function of myoendothelial connections is a topic of great current interest and may relate to the structure of the internal elastic lamina through which the connections must pass. In hypertensive remodelling this must present an organizational challenge. The objective of this paper is to show how the functions of blood vessels depend on their architecture and a continuous interaction of different cell types and extracellular proteins.

Cardiovascular responses to human calf muscle stretch during varying levels of muscle metaboreflex activation

Abstract: The purpose of the present study was to investigate the cardiovascular responses to muscle metaboreflex- and concurrent muscle stretch-induced mechanoreflex activation. Eight subjects (7 males, 1 female) performed 90 s of isometric calf plantarflexion at 0, 30, 50 and 70% of maximum voluntary contraction. During exercise and for 3.5 min postexercise, circulatory occlusion (PECO) was ensured by inflation of a thigh cuff. After 90 s of PECO the calf muscle was stretched for 60 s (Stretch). Heart rate (HR; assessed from ECG), blood pressure (BP; Finapres) and phase of respiratory cycle were recorded. Exercise increased diastolic BP (DBP) from rest by 1+/-0.8, 14+/-2.5, 29+/-3.9 and 35+/-3.6 mmHg, during the 0, 30, 50 and 70% conditions, respectively (ANOVA rest versus exercise, P<0.05). During PECO DBP remained elevated, by 2+/-0.4, 8+/-0.3, 12+/-0.3 and 13+/-0.9 mmHg, respectively. Stretch produced a further increase in DBP that was not different between conditions (3+/-1.4, 2+/-0.8, 3+/-1.0 and 3+/-0.9 mmHg, for the 0, 30, 50 and 70%, respectively). HR increased during exercise but returned to baseline during PECO. HR increased at Stretch onset in all conditions. No EMG was detected from the gastrocnemius and soleus during Stretch. Our data show that the cardiovascular responses to human calf Stretch are independent of the level of concurrent muscle metaboreflex activation.

The neurobiology of human obesity.

Abstract: Earlier ideas that sympathetic nervous system activity is low in human obesity, contributing to weight gain through absence of sympathetically mediated thermogenesis, can now be discounted. The application of sympathetic nerve recording techniques and isotope dilution methodology quantifying neurotransmitter release from sympathetic nerves has established that the sympathetic outflows to the kidneys and skeletal muscle vasculature are activated in obese humans. The cause remains unclear. The adipocyte hormone, leptin, stimulates the sympathetic nervous system in rodents, but whether this applies in humans is uncertain. Cross-sectional studies suggest a quantitative link exists between regional sympathetic nervous tone (most notably in the kidneys) and rates of leptin release, but definitive studies documenting that leptin administration activates the human sympathetic nervous system have not been done. What might be the clinical implications of these new findings? The demonstration that the suppressed sympathetic tone characterizing many experimental models of obesity does not exist in human obesity weakens the case for the use of beta3-adrenergic agonists as thermogenic agents to facilitate weight loss. Although the neurogenic character of obesity-related hypertension is now established, whether antiadrenergic antihypertensive drugs are the preferred agents for blood pressure reduction has not been adequately tested. Multiple site central venous sampling, disclosing release of leptin into the internal jugular veins, led to the demonstration that the leptin gene is also expressed in the brain, in addition to adipocytes. Brain resistance to leptin has been inferred in human obesity, given that overweight is accompanied by high plasma leptin levels. The fact that the genes for leptin and its receptors are normally expressed in the brain in human obesity, and that release of leptin from the brain is actually increased, argues against this. Brain leptin release has the potential to override the peripheral, adipocyte leptin system.

Stability and instability of regulation of intracellular calcium.

Abstract: [Ca2+]i is used as a signal in many tissues. In this review we discuss the mechanisms that regulate [Ca2+]i and, importantly, what determines their stability. Brief mention is made of the effects of feedback gain and delays on stability. The control of cytoplasmic Ca concentration is shown to be generally stable as Ca pumping is essentially an instantaneous function of [Ca2+]i. In contrast, regulation of the Ca content of intracellular stores may be less stable. One example of this is instability in the control of sarcoplasmic reticulum (SR) Ca content in cardiac muscle. An increase of SR Ca content increases the systolic Ca transient amplitude. This in turn decreases Ca influx into the cell and increases efflux, thereby restoring SR Ca to control levels. This feedback system has an inherent delay and is potentially unstable if the gain is increased beyond a certain level. This instability produces Ca transients of alternating amplitude and may contribute to the clinical syndrome of pulsus alternans.

Differences in transductional tropism of adenoviral and lentiviral vectors in the rat brainstem.

Abstract: Adenoviral vectors (AVVs) and lentiviral vectors (LVVs) are highly useful research tools which can be used to investigate the function of specific cell phenotypes in the brain The transductional tropism of viral vectors has a critical impact upon the transgene expression in different brain areas This largely depends on the properties of the viral particles, which for AVVs are most commonly analogous to the serotype 5 adenovirus and, in the case of LVVs, are determined by the envelope used for pseudotyping, for example the vesicular stomatitis virus coat (VSVG) We have created a matching set of shuttle plasmids that allow a one-step transfer of an entire expression cassette between the backbones of AVVs and LVVs This has permitted a fair assessment of the impact of the vector type on tropism for both AVVs and LVVs Thus, the aims of this study were twofold: (i) to develop and demonstrate the validity of a transgene 'swap' system between AVVs and LVVs; and (ii) using this system, to assess the tropism of AVVs and LVVs for neuronal versus glial cell types We have constructed AVVs and VSVG-coated LVVs to express monomeric red fluorescent protein (mRFP) driven by the human cytomegalovirus promoter (hCMV) Transgene expression in neurones and glia in the hypoglossal and dorsal vagal motor nuclei of the rat brainstem was compared by determining the colocalization with immunostaining for the neuronal marker NeuN (neuronal nuclear antigen) and the glial marker GFAP (glial fibrillatory acidic protein) We found that 55% of mRFP-expressing cells transduced with AVVs were immunopositive for GFAP, while only 38% were NeuN-immunoreactive In contrast, when the same expression cassette was delivered by VSVG-coated LVVs, the neurone/glia ratio of mRFP expression was reversed with 56% of mRFP-positive cells identified as neurones and 26% as glia Thus, the present study provides compelling evidence that VSVG-coated LVVs significantly shift transgene expression towards neurones while transduction with AVVs favours glia

ATP regulation of ciliary beat frequency in rat tracheal and distal airway epithelium

Abstract: Ciliary beat frequency (CBF) was measured by video-optical microscopy in rat tracheal and distal airway ciliary cells using a slice preparation. In tracheal ciliary cells (tracheal slice), ATP or 2-methylthio ATP (MeSATP) increased CBF, which was inhibited by suramin (100 microm, an inhibitor of purinergic receptor). Ionomycin (5 microm) or thapsigargin (2 microm) increased CBF similarly. Ca2+-free solution or addition of Ni2+ (1 mm) decreased CBF gradually by approximately 25% and subsequent stimulation with ATP (10 microm) increased CBF transiently. The purinergic agonist experiments demonstrated that ATP increases CBF in tracheal ciliary cells via both P2X and P2Y receptors. ATP increased the intracellular calcium concentration ([Ca2+]i) in tracheal ciliary cells. However, in distal airway ciliary cells (lung slice), ATP did not increase CBF and [Ca2+]i, although a Ca2+-free solution decreased CBF, and ionomycin (5 microm) or thapsigargin (2 microm) increased it. Moreover, acetylcholine (100 microm) did not increase CBF in distal airway ciliary cells, although it increased CBF in tracheal ciliary cells. Terbutaline (10 microm), a selective beta2-adrenergic agonist, increased CBF in both tracheal and distal airway ciliary cells. These observations suggest that the Ca2+-mobilization mechanisms via purinergic or muscarinic receptors of the distal airway ciliary cell may be different from those of the tracheal ciliary cell. In conclusion, the CBF increase is differently regulated in the tracheal and distal airway epithelia of the rat.

Polymorphism in angiotensin II receptor genes and hypertension

Abstract: Molecular variants of individual components of the renin-angiotensin system (RAS) have been thought to contribute to an inherited predisposition towards essential hypertension. The angiotensin II type 1 receptor (AT-1) mediates the major pressor and trophic actions of angiotensin II (Ang II) and at least 50 different polymorphisms have been described in the AT-1 gene (AT(1)R gene); in particular, the C allele of the +1166A/C polymorphism has been associated with the severe form of essential hypertension, but the role of this polymorphism is still ambiguous in pathologies related to high Ang II levels, such as deterioration of renal function, arterial stiffness and hypertrophic cardiomyopathy. A relationship was suggested between AT 1R A1166C polymorphism and the humoral and renal haemodynamic responses to losartan, an AT-1 blocker, as well as with enhanced Ang II vascular reactivity or sensitivity. Polymorphism has also been described in angiotensin II type 2 receptor (AT-2) gene, AT-2 being the mediator for vasodilatation, natriuresis and apoptosis of smooth muscle cells; associations were found between some of these polymorphisms and both hypertension and left ventricular structure. Further evaluation in adequately powered studies is necessary for full assessment of the allelic markers in genes for RAS components, as well as to allow determination of a predisposition to hypertension or related diseases and selection of an appropriate antihypertensive drug for an individual.

Differential cardiovascular responses to stressors in hypertensive and normotensive rats.

Abstract: The aim of this study was to determine to what extent stress-induced cardiovascular responses depend upon rat strain and/or stressor. Spontaneously hypertensive rats (SHRs), Wistar-Kyoto rats (WKYs) and Sprague-Dawley (SD) rats were implanted with telemetry probes in order to measure heart rate and blood pressure changes when exposed to a stressor. The stress protocols employed included handling, air-jet and restraint, where each stressor was repeated over 10 consecutive days. In addition, a heterologous protocol was established whereby the experimental groups having experienced 10 days of air-jet stress were then immediately exposed to 10 consecutive days of restraint. Each stressor caused graded tachycardic and pressor responses in all strains. For all strains, the magnitude and duration of heart rate and blood pressure increases were greatest in the restraint-based protocols while handling and air-jet caused submaximal changes. A comparison between strains indicated that SHRs exhibited prolonged pressor responses to each of the stressor types tested as compared to the normotensive strains. In addition, repeated exposure over 10 days to handling and air-jet in SHRs caused tachycardic and/or pressor responses to adapt to 'normotensive-like' levels. Heterologous restraint stress caused sensitization of cardiovascular responses upon first exposure, predominantly in normotensive strains. Collectively these data show that the magnitude and duration of the tachycardia and pressor responses evoked by the stressors were different within the strains and were also modified by prior experience. In addition, the cardiovascular profiles presented in this study demonstrate that, within each strain, the heart rate response during stress is graded according to the type of stressor encountered.

Reduced voluntary activation of human skeletal muscle during shortening and lengthening contractions in whole body hyperthermia

Abstract: This study examined the effect of whole body hyperthermia on the voluntary activation of exercised and non-exercised skeletal muscle performing a series of lengthening and shortening contractions. Thirteen subjects exercised on a cycle ergometer at 60% of maximal oxygen consumption until voluntary exhaustion in ambient conditions of approximately 40 degrees C and 60% relative humidity. Before and immediately following the cycle protocol, subjects performed a series of 25 continuous isokinetic shortening and lengthening maximal voluntary contractions (MVCs) of the leg extensors and forearm flexors. Voluntary activation for shortening and lengthening contractions for the forearm and leg was assessed prior to and following the 25 MVCs by superimposing a paired electrical stimulus to the femoral nerve and the biceps brachii during additional MVCs. Exercise to exhaustion increased rectal temperature to 39.35+/-0.50 degrees C. Voluntary activation remained unchanged following the prehyperthermia endurance set of shortening and lengthening maximal contractions in both the forearm flexors and leg extensors. Similarly, voluntary activation remained at prehyperthermic levels for the single MVCs immediately following the cycle trial. However, by the time of completion of the posthyperthermia endurance contractions, voluntary activation had declined significantly by 5.87+/-7.56 and 8.46+/-9.26% in the shortening and lengthening phases, respectively, for the leg extensors but not for the forearm flexors. These results indicate that the central nervous system (CNS) reduces voluntary drive to skeletal muscle performing both shortening and lengthening contractions following exercise-induced hyperthermia. The reductions in voluntary activation were only observed following a series of dynamic movements, indicating that the CNS allows for initial and brief 're-activation' of skeletal muscle following exercise-induced hyperthermia.