Showing papers in "Acta Physiologica Scandinavica in 1989"

Ground reaction forces at different speeds of human walking and running

Abstract: In this study the variation in ground reaction force parameters was investigated with respect to adaptations to speed and mode of progression, and to type of foot-strike. Twelve healthy male subjects were studied during walking (1.0-3.0 m s-1) and running (1.5-6.0 m s-1). The subjects were selected with respect to foot-strike pattern during running. Six subjects were classified as rearfoot strikers and six as forefoot strikers. Constant speeds were accomplished by pacer lights beside an indoor straightway and controlled by means of a photo-electronic device. The vertical, anteroposterior and mediolateral force components were recorded with a force platform. Computer software was used to calculate durations, amplitudes and impulses of the reaction forces. The amplitudes were normalized with respect to body weight (b.w.). Increased speed was accompanied by shorter force periods and larger peak forces. The peak amplitude of the vertical reaction force in walking and running increased with speed from approximately 1.0 to 1.5 b.w. and 2.0 to 2.9 b.w. respectively. The anteroposterior peak force and mediolateral peak-to-peak force increased about 2 times with speed in walking and about 2-4 times in running (the absolute values were on average about 10 times smaller than the vertical). The transition from walking to running resulted in a shorter support phase duration and a change in the shape of the vertical reaction force curve. The vertical peak force increased whereas the vertical impulse and the anteroposterior impulses and peak forces decreased. In running the vertical force showed an impact peak at touch-down among the rearfoot strikers but generally not among the forefoot strikers. The first mediolateral force peak was laterally directed (as in walking) for the rearfoot strikers but medially for the forefoot strikers. Thus, there is a change with speed in the complex interaction between vertical and horizontal forces needed for propulsion and equilibrium during human locomotion. The differences present between walking and running are consequences of fundamental differences in motor strategies between the two major forms of human progression.

Physical exercise and brain monoamines: a review

Abstract: A review of the literature on the relationship of exercise to mental health strongly suggests that the two are closely linked. Thus, physical activity has been reported to reduce depression symptoms and anxiety, and to improve coping with stress. Logically, many investigators have then tried to determine the physiological mechanisms that are responsible for this mood-elevating effect of exercise. Among the current hypotheses, those regarding the endorphin and the monoamine systems have received a great deal of attention. On that basis, the respective effects of physical exercise on brain dopamine, noradrenaline and serotonin transmission are reviewed herein. In addition, suggestions are advanced for future research in this field.

Effect of sustained exercise on plasma amino acid concentrations and on 5-hydroxytryptamine metabolism in six different brain regions in the rat.

Abstract: Sustained exercise to fatigue elicits no major differences either in plasma amino acid levels or in brain 5-hydroxytryptamine (5-HT) metabolism between sedentary and endurance-trained animals. Furthermore, 11 weeks of endurance training did not influence the maximal activity of the enzyme monoamine oxidase in the brain areas which were studied. In both sedentary and endurance-trained rats, sustained running to fatigue caused an increase in the plasma concentration ratio of free tryptophan/other large neutral amino acids and an increase in the concentration of tryptophan in the six brain areas that were studied. The increase was similar in the different regions of the brain and averaged 36%. Exercise caused an increase in the levels of 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) in the brain stem (14 and 44% respectively) and hypothalamus (16 and 17% respectively) and an increase in the level of 5-HIAA in the hippocampus (21%) and striatum (28%). Exercise also caused an increase in the level of dopamine in the brain stem (56%) and hypothalamus (46%) and of nor adrenaline in the striatum (59%). Since the levels of 5-HT and dopamine were both increased in the brain stem and hypothalamus, it is possible that these changes may play important roles in the central effects of exercise, including both physical and mental fatigue and effects on mood.

The cold pressor test: effects on sympathetic nerve activity in human muscle and skin nerve fascicles

Abstract: Micro-electrode multi-unit recordings of muscle nerve sympathetic activity (MSA) involved in cardiovascular homeostasis or skin nerve sympathetic activity (SSA) involved in thermoregulation were made in the right peroneal nerve of 48 healthy volunteers during performance of the cold pressor test, i.e. immersion of one hand in ice water (2 +/- 0.5 degrees C) for 1 min. Eleven subjects underwent the same procedure on a second MSA recording occasion. As a rule, immersion evoked an increase in MSA, with a gradual decrease on emersion. The response showed a wide range of variation between and within subjects; the intra-individual difference between first and second immersion on the same recording occasion was up to sevenfold, and from first to second recording up to fivefold. The increase in MSA correlated with the degree of discomfort from the ice water. In nine subjects with a large increase in MSA on ice water immersion, intracutaneous painful electrical stimulation to a level equalling the discomfort from the ice water was added, but it was not accompanied by any change in MSA. The increase in MSA was accompanied by and correlated quite well with an increase in blood pressure. Intra-arterial blood pressure recordings showed that MSA occurred at pressure levels normally associated with total inhibition of MSA, and that an inverse linear relationship between diastolic blood pressure and MSA at rest was abolished during the ice water immersion. SSA showed no consistent change with ice water immersion. It is concluded that the cold pressor test is a powerful activator of MSA, i.e. baroreceptor-governed vasoconstrictor outflow; that MSA contributes to the blood pressure elevation with this manoeuvre; that MSA operates at another blood pressure level during the manoeuvre and that the baroreflex inhibitory level consequently is changed; and that the response is not a reaction to pain only.

Effects of nerve compression or ischaemia on conduction properties of myelinated and non-myelinated nerve fibres. An experimental study in the rabbit common peroneal nerve.

Abstract: Compound action potentials of both myelinated (A) and non-myelinated (C) fibres in the common peroneal nerve of rabbits were studied during and after acute, graded compression of the nerve at 200 or 400 mmHg applied for 2 h or during ischaemia created by nitrogen inhalation or aortic occlusion. Compression of the nerve at 200 mmHg blocked the AI component (large myelinated fibres) after about 23 min, while compression at 400 mmHg shortened this time to 11 min. The A2 component (thinner myelinated fibres) had a lower conduction velocity and a higher resistance to compression. There was just a slight decrease in conduction velocity of the non-myelinated fibres when the nerves were compressed at 200 mmHg for 2 h. However, compression at 400 mmHg for 2 h induced a marked deterioration of amplitude and conduction velocity of the C-fibres. There was an incomplete restitution of function of A- and C-fibres during 2 h of recovery. The thinner myelinated fibres were more susceptible to deprivation of oxygen than the thicker ones, while non-myelinated fibres differed in response according to method of ischaemia induction. It is concluded that non-myelinated fibres are very resistant to compression and a very high pressure (greater than 400 mmHg) is needed to affect these fibres.

Differential release of calcitonin gene-related peptide and neuropeptide Y from the isolated heart by capsaicin, ischaemia, nicotine, bradykinin and ouabain.

Abstract: The influence of various drugs as well as total ischaemia on the outflow of calcitonin gene-related peptide (CGRP), which is present in sensory nerves, and neuropeptide Y (NPY), which is co-stored with noradrenaline (NA), from the isolated guinea-pig heart, was studied in vitro. Capsaicin exposure and total ischaemia for 5-30 min induced a Ca2+-dependent increase in the outflow, suggesting release, of CGRP- but not NPY-like immunoreactivity (LI) from the heart. When characterized by high performance liquid chromatography (HPLC), the CGRP-LI present in heart extracts and the released CGRP-LI by capsaicin eluted in a major peak corresponding to synthetic CGRP. Incubation with morphine, indomethacin or reserpine pretreatment did not influence the capsaicin-evoked release of CGRP-LI. Capsaicin pretreatment depleted the cardiac content of CGRP-LI but not NPY-LI. The increase in perfusate volume observed after 30 min ischaemia in controls was reduced after capsaicin pretreatment. Nicotine exposure induced release of CGRP- as well as NPY-LI in a concentration- and Ca2+-dependent manner. The increased outflow of NPY-LI was not influenced by capsaicin pretreatment. Among other agents tested, bradykinin and ouabain caused increased outflow of CGRP but not of NPY-LI. Noradrenaline, tyramine, histamine, vasopressin, alpha,beta methylene ATP, ATP or adenosine induced changes in cardiac contractility or flow but did not evoke any detectable release of CGRP- or NPY-LI. In conclusion, the release of multiple neuropeptides can be studied in combination with contractile recordings using the isolated perfused guinea-pig whole heart preparation. Activation of cardiac sensory nerves by capsaicin, nicotine, bradykinin and ouabain, as well as ischaemia, induced release of CGRP while nicotine also evoked NPY release.

Maximal voluntary force of bilateral and unilateral leg extension

Abstract: The aims were: (1) to investigate whether the 10-20% lower force during bilateral (BL) as compared to unilateral (UL) leg extension could be due to a general inability to activate fully a large number of muscles simultaneously, (2) to analyse the EMG signal of the quadriceps femoris during leg extensions, (3) to study the BL/UL force ratio in extension of the knee, and (4) to study the BL/UL leg extension force ratio in untrained and trained subjects A 10% lower maximal voluntary isometric force was demonstrated during BL as compared to UL leg extension This force discrepancy did not change when a total arm load of 250 N was applied simultaneously Nor did the absolute force levels change, which indicates that the lower BL leg extension force is not due to a general mechanism of reduced activation with an increased number of muscles recruited in maximal voluntary contractions Integrated EMG activity, mean power frequency and root mean square value of the EMG amplitude did not differ between UL and BL leg extensions The knee extension force was slightly greater (4%) during BL than UL contractions These findings are arguments against a reduced activation of the knee extensor muscles being the cause of the lower bilateral leg extension force No differences in BL/UL force ratio were noted between groups of untrained and trained subjects despite the fact that several of the trained groups do different forms of BL leg extensions regularly Thus, it does not appear that training readily affects the BL/UL leg extension force ratio

Bistable firing properties of soleus motor units in unrestrained rats.

Abstract: EMG recordings from single motor units in the soleus muscle were performed in alert unrestrained rats. A cuff electrode around the tibial nerve and subcutaneously placed electrodes in the foot permitted stimulation of afferent fibres. The movements of the rat and the simultaneous EMG activity were displayed together on a video monitor. Most motor units were tonically active for extended periods during quiet standing. During tonic discharge, maintained shifts between stable low (8-12 Hz; quartiles) and high (16-22.8 Hz) frequency ranges were initiated by short-lasting synaptic excitation of the motoneuron pool by stimulation of Ia afferents, or inhibition by stimulation of skin afferents. The shifts were not related to gross limb movements. This phenomenon is referred to as a bistable firing pattern. Bistable firing also occurred spontaneously during quiet standing. Typically the firing frequency shifted between a low (9-12.5 Hz) and a high (20-24.5 Hz) mode. During recordings of simultaneous activity in two units, spontaneous and stimulus-induced frequency jumps causing maintained changes in firing frequency were regularly seen to occur in one unit, while the frequency in the second unit was unchanged or only phasically influenced. These results demonstrate for the first time a bistable firing pattern during postural activity in the intact animal. The firing pattern closely resembles the bistable behaviour described in spinal motoneurons in reduced preparations, where it is due to the presence of a plateau potential. This suggests that the bistable firing is unexplained by plateau potentials also in the intact animal.

Renal interaction between sympathetic activity and ANP in rats with chronic ischaemic heart failure

Abstract: The diuretic and natriuretic effects of r-alpha-ANP (99-126) were investigated in rats with chronic ischaemic heart failure (IHF) produced by left coronary artery ligation. The plasma concentration of immunoreactive ANP (IrANP) was significantly higher, 91.8 +/- 16.0 pm in the IHF rats compared to 31.0 +/- 4.9 pm in sham-operated controls. In the control rats, ANP infusion (0.25-1.0 micrograms kg 1 mm 1) increased urine flow rate (V) and urinary sodium (UNa V) excretion. At the highest dose level, both V and UNa V were increased approximately fivefold. The diuresis and natriuresis seen in the control group after the infusion of ANP were blunted in the IHF rats. A bilateral surgical renal denervation in the IHF rats did not alter the renal dopamine levels, but induced a significant decrease in renal noradrenaline content, and almost completely restored the renal responsiveness to the ANP infusions. We conclude that renal denervation reversed the blunted renal excretory response to ANP in IHF rats. Thus, in experimental IHF, there seems to be a functional antagonism between efferent renal sympathetic nerve activity and ANP.

Topographical localization of muscle glycogen: an ultrahistochemical study in the human vastus lateralis.

Abstract: The fine structural pattern of glycogen storage in resting and sprint-exercised human vastus lateralis muscle fibres of different types was analysed using ultrahistochemical methods. Three male subjects (31-36 years) performed 60 consecutive, supramaximal bouts of bicycle exercise, each starting every 1 min and having a duration of 8 s (including approximately 3 s of acceleration). The load was estimated to correspond to 200% of VO2-max. Five other subjects (22-27 years) constituted controls. Ultrathin sections stained with periodic acid-thiosemicarbazide-silver proteinate (PA-TSC-SP) clearly revealed a compartmental distribution of glycogen. Glycogen is stored at five topographically, and probably also functionally, different locations. They are the subsarcolemmal, intermyofibrillar, para-Z-disc, N2-line, and H-zone spaces. During the exercise, glycogen from the N2-line and para-Z-disc locations is preferentially utilized. Serial sections stained with uranyl acetate and lead citrate demonstrated that glycogen stores of the type 2 fibres were more depleted than those of type 1 fibres. The implications of the differential intracellular glycogen storage are discussed

Very rapid net transcapillary fluid absorption from skeletal muscle and skin in man during pronounced hypovolaemic circulatory stress.

Abstract: High levels (110-120 cmH2O) of lower body negative pressure (LBNP) were used in male volunteers (n = 7) to produce pronounced hypovolaemic circulatory stress in an attempt to reveal the potential in man for compensatory absorption of extravascular fluid from skeletal muscle and skin as studied in the upper arm by plethysmographic technique. LBNP evoked clear-cut hypovolaemic symptoms or even accidental syncope as well as a marked tachycardiac response and a significant fall in systolic blood pressure. In the studied arm there was concomitantly a very rapid net transcapillary absorption of extravascular fluid into the circulation at an average rate of 0.35 ml min-1 100 ml-1 soft tissue during 5 min of LBNP exposure. These data demonstrate an amazingly great potential to increase plasma volume by 'autotransfusion' of fluid from tissue to blood, as may be visualized by extrapolation of the data from the arm to apply to the whole mass of skeletal muscle and skin in the body. The observed absorption rate would then correspond to a total fluid gain of no less than 700 ml within a period no longer than 5 min. At present, however, there is no evidence to indicate that such impressive fluid volumes can be rapidly transferred from the extra-to the intravascular space after actual blood loss.

Differential release of coexisting neurotransmitters: frequency dependence of the efflux of substance P, thyrotropin releasing hormone and [3H]serotonin from tissue slices of rat ventral spinal cord.

Abstract: In few systems has the release of coexisting classical and peptide neurotransmitters been studied. Here the release of substance P-like immunoreactivity (SP-LI), thyrotropin releasing hormone-like immunoreactivity (TRH-LI) and [3H]serotonin ([3H]5-HT) from tissue slices of rat ventral spinal cord was investigated in a superfusion system. The slices were stimulated electrically with field stimulation (900 pulses, 2 ms duration, 36 V) at frequencies between 0.25 Hz and 40 Hz. The evoked fractional release of SP-LI increased significantly from 0.46 to 1.24% of the total tissue store when the frequency of stimulation was changed from 3 to 10 Hz, while the evoked fractional release of TRH-LI increased significantly from 0.28 to 0.71% of the total tissue store with increasing frequency of stimulation between 0.5 and 3 Hz. The evoked fractional release of [3H]5-HT did not show any significant change when the frequency of stimulation was changed in the frequency range of 0.25-40 Hz but remained between 5.6 and 7.2% of the total tissue store. It appears that at frequencies lower than 0.5-1 Hz these 5-HT/SP/TRH neurons may function predominantly as serotonergic neurons. At 3 Hz stimulation with 900 pulses the extracellular Ca2+ concentration required for half-maximal release of [3H]5-HT was 1.2 mmol l-1, while for half-maximal release of SP-LI significantly higher concentrations of Ca2+ (4.2 mmol l-1) would be required.(ABSTRACT TRUNCATED AT 250 WORDS)

Oestrogen-induced changes in muscarinic receptor density and contractile responses in the female rabbit urinary bladder

Abstract: Mature ovariectomized rabbits were treated for 1, 4 or 8 weeks with oestrogen, and the effects on contractile responses and on muscarinic receptor density in the isolated urinary bladder were studied. Oestrogen treatment caused a significant increase in the weight of the bladders. The responses to K+ (124 mM) were depressed, but not the maximum responses to carbachol. The frequency-response curve to electrical stimulation was shifted to the right after 4 and 8 weeks of treatment, but the maximum response was not reduced. There was also a (non-significant) shift to the right of the carbachol concentration-response curve. Pre-treatment with scopolamine revealed a significant reduction of the non-cholinergic response to electrical stimulation after oestrogen treatment compared to controls. Binding of [3H]quinuclidinyl benzilate (QNB) was saturable and of high affinity. There were no changes in apparent dissociation constant after oestrogen treatment. However, the muscarinic receptor density decreased already after 1 week of treatment and was only 10% of the control after 4 weeks. It is concluded that oestrogen treatment causes a down-regulation of muscarinic receptors in the rabbit urinary bladder, but the consequences for contractile activation through muscarinic receptors seem to be small.

Endothelin: presence in human umbilical vessels, high levels in fetal blood and potent constrictor effect.

Abstract: L'endotheline est un agent vasoconstricteur. Lors de l'accouchement, lorsque la circulation placentaire est interrompue et les arteres ombilicales obstruees, il pourrait y avoir l'intervention d'un agent vasoconstricteur tel que l'endotheline. La distribution de l'endotheline est etudiee ici dans les vaisseaux ombilicaux et le plasma fœtal humain. Ses effets vasoconstricteurs sont testes in vitro sur les vaisseaux ombilicaux

Sarcoplasmic reticulum of human skeletal muscle: age-related changes and effect of training.

Abstract: The effect of ageing on human skeletal muscle was investigated using needle biopsies from young and aged subjects and from aged subjects trained with different activity patterns. Histochemical staining for myofibrillar ATPase of ageing m. vastus lateralis demonstrated an unchanged fibre type distribution but a selective atrophy of type IIa and type IIb fibres. Analysis of myosin heavy chain (MHC) composition showed that type I MHC increased with ageing (P less than 0.05). The relative content of the MHC isoforms correlated with the relative area of the respective fibre types. Sarcoplasmic reticulum (SR) proteins were investigated in muscle extracts by electrophoretic and immunoblotting techniques. When compared to a young control group (28 +/- 0.1 years old, n = 7) blots of post-myofibrillar supernatant proteins probed with polyclonal antibodies to the rabbit fast SR Ca-ATPase, a marker of extrajunctional SR, showed that the content of Ca-ATPase was significantly lower (P less than 0.05) in the old control group (68 +/- 0.5 years old, n = 8). On the other hand the content of calsequestrin (CS), the major intraluminal protein of SR terminal cisternae (TC), and of the 350-kDa ryanodine-binding protein, which is localized in the junctional regions of TC, did not show a concomitant decrease. These results suggest that ageing differentially affects extrajunctional and junctional SR of human skeletal muscle. These age-related changes were not observed within a group of old strength-trained subjects.

Lipoxin A4 inhibits leukotriene B4,‐induced inflammation in the hamster cheek pouch

Abstract: La lipoxine A 4 dilate les arterioles in vivo sans modifier la permeabilite vasculaire. L'action de la lipoxine A 4 est etudiee sur le role inflammatoire du leukotriene B 4 , chez le hamster

Mechanoreceptive units in the human infra-orbital nerve.

Abstract: Eighty-four low-threshold mechanoreceptive afferents innervating facial hairy skin or the red zone of the lip were recorded with micro-electrodes from the human infra-orbital nerve. Based on their responses to skin indentations, the units were classified as slowly or fast-adapting, with small or large receptive fields. The responses to hair movement, skin stretching and contraction of facial muscles were also studied. Both hairy skin and the red zone were innervated by slowly and by fast-adapting units. The innervation density was found to be highest at the corner of the mouth and on the upper lip. Slowly adapting units with small fields in hairy skin were most common and included units responding to sustained hair displacement. These units are suggested to have two types of end-organs, either pilo-Ruffini endings or Merkel cell-neurite complexes. The slowly adapting units with large fields were spontaneously active stretch receptors and may have corresponded to Ruffini corpuscles, although the possibility of other, intramuscular, receptors could not be ruled out. Only one afferent possibly innervated a Pacinian corpuscle. Most mechanoreceptors were also activated by skin stretching or contraction of facial muscles. Many of the slowly adapting units with small fields responded to the onset and release of stretch, whereas their discharge in response to sustained stretching adapted more or less completely. Spontaneously active units had the most sustained stretch response. It is concluded that several types of cutaneous mechanoreceptors can operate as sensitive proprioceptors of importance for facial kinaesthesia and motor control.

Effects of ageing and physical training on rat skeletal muscle. An experimental study on the properties of collagen, laminin, and fibre types in muscles serving different functions.

Abstract: The purpose of the present investigation was to study the effects of both advancing age and life-long endurance training on the connective tissue and fibre composition of two types of rat skeletal muscle. In particular, additional evidence was sought on age- and training-induced transformations of muscle fibres, and on the significance of intramuscular collagen in muscle functioning. For this purpose a combined study of exercise and ageing throughout the life-span of the experimental animals was constructed. To gain a broad view of muscle responsiveness the muscle fibre types, the estimates of different biochemical and histological properties of collagen as well as of the passive mechanical properties of both a slow (m. soleus = MS) and a fast (m. rectus femoris = MRF) skeletal muscle were determined. The results can be summarized as follows: 1) The percentage of type I fibres in MS increased from about 60% in one-month-old rats up to about 90% in the untrained and almost 100% in the trained rats at ages between 4 and 10 months. In adult animals the proportion of type I fibres was significantly higher in the MS of the trained than untrained animals. In the slow area of MRF, the percentage of type IIA fibres increased from a mean value of below 40% in one-month-old rats to above 50% in the untrained and near to 70% in the trained rats at the age of 24 months. Correspondingly, the proportion of type IIB fibres decreased with both age and training. In both types of muscles, there was a tendency towards smaller cross-sectional areas for the predominant fibre type in the trained rats when compared to the untrained rats. Consequently, the long-term endurance training used did not reverse the age-related shift in muscle fibre composition but clearly accelerated the fibre transformation towards more fatigue-resistant muscle fibres with slower contractile speeds. Nevertheless, the slowing due to endurance training is not necessarily deleterious, as different mechanisms may be involved in these age- and training-related alterations. The former appears to involve degenerative changes in the neuromuscular system whereas endurance-type activity could assist in the maintenance of the low-threshold neural activity important for the expression of slow contractile characteristics. 2) The slow postural soleus contained more collagen compared with the fast locomotor rectus femoris muscle. The concentration of total collagen as well as the area-fractions of both endomysium and perimysium were larger in MS than in MRF.(ABSTRACT TRUNCATED AT 400 WORDS)

Marked regional heterogeneity in blood flow within a single skeletal muscle at rest and during exercise hyperaemia in the rabbit

Abstract: In 1985 both Pendergast et al. and Piiper et al. described a major regional heterogeneity in blood flow within single skeletal muscles both at rest and during exercise. Based on the microsphere method they described large variations in blood flow between muscle samples as large as 1 g each. The aims of the present study were: 1 To test this notion of regional heterogeneity in microsphere deposition within single skeletal muscles both at rest and during exercise. 2 To compare the distribution of microspheres with other blood flow tracers. 3 To test whether or not any heterogeneity was due to vasomotion in small arteries or arterioles. Microspheres were infused into anaesthetized rabbits over either 10, 30 or 120 s, or 10 min. Exercise was mimicked by tetanic contractions obtained by electrical stimulation of the motor nerves. Three hindleg muscles were divided into samples of 0.25 g each. Regional heterogeneity was expressed as the coefficient of variation corrected for statistical distribution of microspheres (CVc). The CVc at rest was about 0.34. The CVc was unaffected by the various infusion periods and did not change during exercise. Simultaneous infusions of microspheres and 86Rb+ or antipyrine gave high correlations between the two blood flow tracers, with all r values exceeding 0.83 (n= 18). We conclude that the microsphere method provides reliable estimates for regional blood flow within single skeletal muscles. The distribution of blood flow was markedly heterogeneous both at rest and during exercise. The heterogeneity in blood flow was apparently not a result of vasomotion.

Formation of inosine monophosphate (IMP) in human skeletal muscle during incremental dynamic exercise

Abstract: The influence of exercise intensity on the accumulation of inosine monophosphate (IMP) in human skeletal muscle has been investigated. Ten men cycled at workloads corresponding to 40%, 75% and 100% of their maximal oxygen uptake (VO2 max). Muscle IMP was below the detection limit (less than 0.01 mmol kg-1 dry wt) at rest and after exercise at 40% of VO2 max, but increased to 0.26 +/- 0.06 (mean +/- SEM) and 3.50 +/- 0.51 mmol kg-1 dry wt after exercise at 75% and 100% of VO2 max respectively. Accumulation of IMP corresponded to a similar decrease in the total adenine nucleotide content. The muscle content of IMP was positively related to lactate and negatively related to phosphocreatine (PCr). IMP was formed in both fibre types, but the IMP content at fatigue was about twice as high in type II fibres as in type I fibres. It was concluded that the IMP content of human skeletal muscle is very low at rest and after low-intensity exercise, but increases after moderate and high-intensity exercise. In contrast to rat muscle, where deamination of AMP predominantly occurs in the fast-twitch muscle fibres, IMP is formed during exercise in both fibre types in human muscle. Accumulation of IMP appears to reflect an imbalance between the rate of utilization and the rate of regeneration of ATP.

Enzyme activities in type I and II muscle fibres of human skeletal muscle in relation to age and torque development.

Abstract: The quadriceps muscles from 20- 30- and 70-year-old clinically healthy men and women were studied regarding maximal isometric and isokinetic muscle torque in Newton metres (Nm), morphology and enzyme activity. Biopsy specimens were taken from the vastus lateralis muscle and freeze-dried, and individual fibres were dissected out and identified as type I or type II. The activities of citrate synthase (CS), 3-OHacyl-coA dehydrogenase (HAD), lactate dehydrogenase (LDH), myokinase (MK) and creatine phosphokinase (CPK) were determined in pools of type I and type II fibres. In both age groups a higher oxidative (CS, HAD, 1.3-1.5 x) and a lower glycolytic (LDH, 0.7 x) capacity was found in type I than in type II fibres. The myokinase activity was higher in type II (2 x) than in type I, whereas CPK activity was similar. The young men showed higher CS activity in both type I and type II fibres (1.5 x) and higher CPK activity in type I fibres (1.4 x) than the young women. There were only minor changes in oxidative or glycolytic capacities in relation to age. Myokinase was the only enzyme that decreased markedly with age in both pools of fibre types. Type II fibre area and mean fibre area correlated significantly to muscle torque in both sexes. In men, myokinase activity in type II fibres was significantly correlated to type II fibre area and to maximal muscle torque.

The metabolic relation between hypoxanthine and uric acid in man following maximal short‐distance running

Abstract: Hellstn Westing, Y., Ekblom, B. & Sjodin, R. 1989. The metabolic relation between hypoxanthine and uric acid in man following masimal short-distance running. Acta Physiol Scand 1–37, 341–345. Received 10 March 1989, accepted 24 June 1989. ISSN 0001–0772. Department of Physiology III, Karolinska Institute, and Swedish Defence Research Establishment, Stockholm, Sweden. This study was performed to asscss the metabolic relation between hypoxanthine and uric acid following short-distance maximal running. Eleven trained males, mean age 22 years (16–31), were instructed to run 800 m in the shortest time possible. Bood samples were collected before warm-up, before the run, immediately after the run and periodically up to 24 h following the run. Blood lactate was determined after warm-up, and at 5, 10, and 30 min following the run. Mean Vo2 mas for the subjects was 65.8 (4.7) (SD) ml kg-1 min-1 and mean oxygen demand for the running was 118 (8)%, of Vo2 may. Plasma hl-poxanthine levels rose from 3.3 (1.4) to a peak of 48.2 (19.0)μmol l-1 at to min following the run and at 180 min had almost returned to pre-tun levels Plasma uric acid levels rose from a pre-run value of 267 (34) to a peak value of 131 (87) μmol l-1 at 45 min following the run. Uric acid concentrations had not returned to normal at 10 h following the run. The hlood lactate level peaked at j min with 13.7 (2.0) mmol l-1. The results obtained in this study indicate a metabolic relationship between the formation of hypoxanthine and the formation of uric acid. The data also indicate that xanthine osidase is active following short-distance intensive running.

Transmission of externally applied negative pressure to the underlying tissue. A study on the upper arm of man.

Abstract: The transmission to the underlying tissue of externally applied negative pressure (2-50 mmHg) was studied in 15 male volunteers on a segment of the upper arm 8 cm in length enclosed in a clear plastic cylinder sealed hermetically against the skin. Pressure recordings were obtained from the anterior and posterior tissue compartments from sites along the entire tissue segment exposed to negative pressure at depths from the skin surface ranging from 5 to 62 mm. Reduction of pressure in the cylinder caused rapid decline, and cessation of external negative pressure rapid recovery, of tissue pressure. In the steady-state phase of negative tissue pressure, the applied external pressure change was in the great majority of experiments transmitted fully or almost fully to the tissue, regardless of from which position along the tissue segment and from which tissue depth pressure was recorded and regardless of the magnitude of the applied negative pressure. The described findings suggest that a defined reduction of atmospheric pressure leads to a similar alteration of vascular transmural pressure and that the technique of external negative pressure can be used for not only qualitative but also quantitative studies of local circulatory reactions evoked by such transmural pressure changes.

Centrally administered endothelin-1 produces lesions in the brain of the male rat.

Abstract: L'endotheline-1 est un vasoconstricteur dont les recepteurs sont cerebraux. Son effet est etudie ici sur les fonctions respiratoires apres administration intracerebrale chez le Rat

Neurotensin modulates the binding characteristics of dopamine D2 receptors in rat striatal membranes also following treatment with toluene

Abstract: The effects of neurotensin in vitro (1-100 nM) on the binding characteristics of [3H]N-propylnorapomorphine ([3H]NPA) were analysed in striatal membrane preparations of the adult male rat. Subsequently, it was investigated whether the modulatory effects of 10 nM neurotensin on [3H]NPA binding were altered by treatment with toluene in vivo (80 p.p.m., 3 days, 6 h day-1) and in vitro (19 mumol ml-1). Displacement of [3H]NPA binding by raclopride (IC50 about 15 nM) and SCH 23390 (without effect) indicated that [3H]NPA labelled only D2 dopamine receptors in the present study. Neurotensin was found to reduce the affinity of D2 receptors with a maximum response at 10 nM. At this concentration the KD value was increased by 30-40% without any consistent changes in the number of binding sites. The modulatory effect of neurotensin remained intact also following toluene treatment in vivo and in vitro, although at a higher KD range, since toluene alone increased the KD value of [3H]NPA binding by 40-50%. Thus, the mechanisms mediating the effects of neurotensin and toluene on the D2 receptor are likely to be different. When neurotensin and toluene treatments were combined, the KD values of [3H]NPA binding were about twice as high as in non-treated controls. These additive effects may lead to a severely decreased efficiency of dopamine D2-mediated neurotransmission in vivo.

Regional differences in glucocorticoid receptor immunoreactivity among neuropeptide Y immunoreactive neurons of the rat brain.

Abstract: By means of two-colour immunocytochemistry using a mouse monoclonal antibody directed against the rat liver glucocorticoid receptor (GR) and a rabbit polyclonal neuropeptide Y (NPY) antiserum combined with the biotin-avidin immunoperoxidase and a double immunofluorescence procedure, it has been possible to demonstrate nuclear GR immunoreactivity (IR) in neurons showing cytoplasmatic NPY IR in rat brain. The majority of NPY immunoreactive perikarya of the medial parvocellular part of the arcuate nucleus, locus coeruleus and the rostral and caudal part of the ventrolateral medulla oblongata contained strong nuclear GR IR. Many of the NPY immunoreactive neurons present in the subnuclei of the nucleus tractus solitarius also contained nuclear GR IR, while most of the NPY immunoreactive perikarya of the cerebral cortex and all of the neostriatum appeared to lack GR IR. These results indicate that NPY immunoreactive neurons in the upper and lower brain stem, but not in the cerebral cortex and in the neostriatum may be directly involved in mediating central effects of glucocorticoids.

Adrenergic and non-adrenergic mechanisms in sympathetic vascular control of the nasal mucosa.

Abstract: 1. Co-existence of NA and NPY-LI was observed in the dense network of sympathetic nerves around both resistance and capacitance vessels in the nasal mucosa from most species including man. NPY-LI seems also to be present together with VIP-LI and PHI-LI in periglandular and some perivascular parasympathetic fibres in some species. 2. A new in vivo model was developed in the pig which allowed parallel recordings of arterial blood flow (BF), capacitance function (V) and superficial movement of blood cells (LDF signal) of the nasal mucosa upon SNS and/or local intra-arterial injection of various pharmacological agents. SNS reduced both BF and V. The V response was maximal already at low frequency. The LDF signal was increased when the SNS-evoked BF reduction was under 40% but was reduced upon larger BF response. After pretreatment with the alpha-adrenoceptor antagonist PBZ, the vascular responses to SNS were significantly attenuated but clear-cut reductions of BF, V and LDF responses remained even to a single impulse. Exogenous NA induced dose-dependent reductions of the BF, V and LDF signal, which were abolished by PBZ treatment. ATP caused biphasic vascular effects with short-lasting vasoconstriction followed by vasodilatation. NPY and mATP caused reduction of the vascular parameters via non-adrenergic mechanisms. 3. A frequency-dependent increase of NA overflow was observed in the nasal venous effluent upon SNS in control pigs, whereas detectable release of NPY-LI occurred only at high frequency. Pretreatment with PBZ significantly increased the SNS-evoked NA and NPY-LI overflow, while DMI enhanced both the functional response and NA release but reduced the NPY-LI overflow. These data suggest that NA and NPY release in the pig nasal mucosa is regulated by prejunctional alpha-adrenoceptor mechanisms. During tachyphylaxis to mATP, the NA and NPY-LI overflow and the vasoconstrictor responses to SNS were unmodified in controls. 4. Reserpine pretreatment induced a marked depletion of both NA and NPY-LI in the pig nasal mucosa. The reduction of NA was not influenced by preganglionic denervation while the depletion of NPY then was prevented. Slowly developing, frequency-dependent and long-lasting vascular responses remained (up to 80% of control) upon SNS in reserpinized and decentralized animals. In these animals, the NA overflow was abolished while release of NPY-LI was enhanced. Stimulation with irregular bursts, caused both larger vascular responses and more NPY-LI overflow in comparison with continuous stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of growth hormone on skeletal muscle. I. Studies on normal adult rats

Abstract: A study was made on the effects of recombinant human growth hormone (rhGH) on fast and slow skeletal muscle in normal adult female rats. Daily injections of 4 IE of rhGH over 36 days resulted in increased levels of insulin-like growth factor I in serum and increased body weight. Morphometric analysis of the muscle fibres of the extensor digitorum longus (EDL) and soleus muscles revealed a significant increase in diameter of both type 1 and type 2 fibres in both muscles. The DNA: protein ratio and the number of satellite cells:muscle fibre in cross-sections was increased in the GH-treated rats in relation to controls. The results show that rhGH has pronounced effects on both cell proliferation and muscle fibre growth in skeletal muscle of normal adults rats.

Capsaicin-induced vasodilatation of human coronary arteries in vitro is mediated by calcitonin gene-related peptide rather than substance P or neurokinin A.

Abstract: In the present study the possible influence of capsaicin on human arterial coronary tone in vitro was studied in relation to the vasodilatory properties of calcitonin gene-related peptide (CGRP), substance P (SP) or neurokinin A (NKA) In addition, the influence of vasoactive intestinal polypeptide (VIP) and somatostatin (SOM) on the arteries was investigated CGRP application to potassium-pre-contracted human epicardial coronary arteries (04-06 mm in inner diameter) induced a concentration-dependent, long-lasting relaxation SP also relaxed these pre-contracted arteries, but the relaxation was transient and tachyphylaxis developed rapidly upon repeated administration SP tachyphylaxis did not influence the relaxatory effects of CGRP Furthermore, pre-incubation with gossypol, an inhibitor of the formation and release of endothelium-derived relaxing factors (EDRF), completely abolished the effects of SP without influencing the dilatory action of CGRP NKA only induced a very minor relaxation of the pre-contracted arteries Both VIP and SOM concentration-dependently relaxed the pre-contracted arteries Capsaicin evoked a relaxation of the potassium-pre-contracted arteries This effect was not influenced by SP tachyphylaxis or gossypol incubation Thus, CGRP but not SP mimics the vasodilatory effects of capsaicin on human coronary arteries This suggests that CGRP rather than SP is likely to mediate the relaxatory effects seen upon activation of cardiac sensory nerves