bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Temperature on Muscle Metabolism During Submaximal Exercise in Humans
Authors: Starkie Rebecca L. , Hargreaves Mark , Lambert Donna L. , Proietto Joseph , Febbraio Mark A. 
Published: May 2004

SUMMARYTo study the effect of temperature on muscle metabolism during submaximal exercise, six endurance‐trained men had one thigh warmed and the other cooled for 40 min prior to exercise using water‐perfused cuffs. One cuff was perfused with water at 50‐55°C (HL) with the other being perfused with water at 0°C (CL). With the cuffs still in position, subjects performed cycling exercise for 20 min at a work load corresponding to 70% VO2,peak (where VO2,peak is peak pulmonary oxygen uptake) in comfortable ambient conditions (20‐22°C). Muscle biopsies were obtained prior to and following exercise and forearm venous blood was collected prior to and throughout the exercise period. Muscle temperature (Tmus) was not different prior to treatment, but treatment resulted in a large difference in pre‐exercise Tmus (difference = 6·9 ± 0·9°C; P < 0·01). Although this difference was reduced following exercise, it was nonetheless significant (difference = 0·4 ± 0·1°C; P < 0·05). Intramuscular [ATP] was not affected by either exercise or muscle temperature. [Phosphocreatine] decreased (P < 0·01) and [creatine] increased (P < 0·01) with exercise but were not different when comparing HL with CL. Muscle lactate concentration was not different prior to treatment nor following exercise when comparing HL with CL. Muscle glycogen concentration was not different when comparing the trials before treatment, but the post‐exercise value was lower (P < 0·05) in HL compared with CL. Thus, net muscle glycogen use was greater during exercise with heating (208 ± 23 vs. 118 ± 22 mmol kg−1 for HL and CL, respectively; P < 0·05). These data demonstrate that muscle glycogen use is augmented by increases in intramuscular temperature despite no differences in high energy phosphagen metabolism being observed when comparing treatments. This suggests that the increase in carbohydrate utilization occurred as a direct effect of an elevated muscle temperature and was not secondary to allosteric activation of enzymes mediated by a reduced ATP content.
Effects of Acute and Chronic Starvation on Central and Peripheral Noradrenaline Turnover, Blood Pressure and Heart Rate in the Rat
Authors: El Fazaa S. , Somody L. , Gharbi N. , Kamoun A. , Gharib C. , Gauquelin‐koch G. 
Published: May 2004

SUMMARYWhen faced with stress, an organism calls upon several mechanisms to maintain biological homeostasis. The cardiovascular system is the first to respond usually with an increase in arterial pressure and tachycardia. Therefore we investigated the central and peripheral sympathetic responses to acute and chronic starvation in Wistar rats. The noradrenaline (NA) turnover rate was determined in different catecholaminergic nuclei (A1, A2, A5, A6) as well as the arterial blood pressure and heart rate modifications. During acute starvation (3 days of starvation), the NA turnover was increased in the A1 and rostral A2 nuclei as well as in ventricles and kidneys and decreased in the A6 nucleus. During chronic starvation (4 consecutive cycles of 3 days of starvation plus 1 day of feeding), the NA turnover was increased in the A5 and caudal A2 nuclei as well as in ventricles and atria and decreased in the A1 nucleus and kidneys. The arterial blood pressure revealed a gradual decrease during the first 3 days of fasting but the heart rate was not modified. We conclude that starvation should be considered as an unusual state of stress because of the absence of locus coeruleus response (A6 nucleus) despite its well‐defined role in stress reactions. One of the manifestations of these central and peripheral noradrenergic changes is the change in blood pressure during the starvation‐feeding cycles.
High Activity K+ Channels in Rat Hippocampal Neurones Maintained in Culture
Authors: Wann K. T. , Goodwin P. A. , Richards C. D. 
Published: May 2004

SUMMARYA channel was identified in cell‐attached recordings in rat hippocampal neurones maintained in culture. This channel, which was highly active at the resting membrane potential, was present in most (73%) patches studied. The channel was characterized by long duration openings and a high open probability (Po, mean value 0·73 at ‐70 mV) at negative patch potentials with mild voltage dependence over the range ‐40 to ‐120 mV. It showed inward rectification. There were up to five active channels in cell‐attached recordings in experiments where the cells were bathed in sodium‐containing Locke solution. The single channel conductances in cell‐attached recordings with 140 or 40 mM K+ in the patch pipette were 26 and 12 pS, respectively. The channel was therefore selective for K+ over Na+. The channel was not permeable to Rb+ ions. The single channel conductance was 24 pS in excised inside‐out patches bathed in symmetrical K+ (140 mM) solutions. Examination of the channel kinetics revealed that both the open and closed time distributions could be fitted by the sum of three exponentials, there being no pronounced voltage sensitivity between ‐60 and ‐120 mV. The 26 pS K+ channel was insensitive to extracellular TEA, apamin, 4‐AP and dequalinium. Neither was it sensitive to intracellular Ca2+. Extracellular Ba2+ was effective in reversibly blocking the channel, the IC50 being 2.0 mM. There was no obvious effect of bath application of the K+ channel opener, lemakalim, or a cAMP analogue. This channel appears to contribute a significant proportion (at least 30%) of the resting conductance in these neurones.
Effects of Variations in Live Weight Gain on Bone Growth and Composition and on Markers of Bone Turnover in Lambs
Authors: Nicodemo M. L. F. , Scott D. , Buchan W. , Duncan A. , Robins S. P. 
Published: May 2004

SUMMARYGrowing lambs were fed the same diet at intakes supporting mean live weight gains of 0·1, 0·2 and 0·3 kg day−1, representing slow, intermediate and fast growth groups, respectively. The effects on bone growth and composition, and on blood and urinary bone marker concentrations or excretion rates were monitored. Compared with the slow‐growing lambs, the higher intake group grew twice as fast, had higher rates of bone growth (indicated by external metatarsal length), and larger and heavier bones at slaughter. Bones from fast‐growing animals had higher collagen and deoxypyridinoline concentrations, and lower Ca:collagen, Ca:P and pyridinoline : deoxypyridinoline ratios, indicating a less mature bone compared with the slow‐growing lambs. Bone growth rate had no effect on plasma osteocalcin, bone‐specific alkaline phosphatase or growth hormone concentrations, nor on the urinary excretion of pyridinoline and deoxypyridinoline. The results for plasma markers may be explained by an increase in blood volume linked with increased body weight.
The Use of a Deuterium Tracer Technique to Follow the Fate of Fluids Ingested by Human Subjects: Effects of Drink Volume and Tracer Concentration and Content
Authors: Lambert C. P. , Ball D. , Leiper J. B. , Maughan R. J. 
Published: May 2004

SUMMARYDeuterium oxide (2H2O) has been added to drinks as a tracer for water to estimate the availability to the body water pool of ingested fluids, but doubts have been raised as to the reliability of the method. The present investigation evaluated the effects of systematic variations in the volume of fluid consumed and the amount and concentration of added tracer on the rate of accumulation of tracer in arterialized blood after ingestion of a labelled drink. Three separate experiments were undertaken. In expt 1, six healthy men ingested on separate occasions 200, 400 and 800 ml of a dilute glucose‐electrolyte solution: all test drinks contained the same concentration (40 g l−1) of 2H2O. In expt 2, six healthy men ingested 200, 400 and 800 ml of the same glucose‐electrolyte drink: each drink contained 8 g of 2H2O so that the concentration, but not the amount, of 2H2O differed between treatments. In expt 3, six healthy men ingested 400 ml of the same drink on three separate occasions: each drink contained 8, 16 or 32 g of tracer so that amount and concentration of 2H2O both varied. Arterialized venous blood samples were collected for the determination of deuterium (2H) concentration before ingestion of the test drink and at intervals for 120 min after ingestion. All trials for each of the experiments were conducted in the morning after an overnight fast and trials were in randomized order and separated by 7 days. In expt 1, the blood 2H concentration at all time points from 2 min after ingestion of the test drink onwards was higher for the drink containing 32 g 2H2O than for the drink containing 16 g 2H2O, which in turn was higher than after ingestion of the drink containing 8 g of 2H2O. In expt 2, no significant differences between treatments were observed at any time. In expt 3, the rate of 2H accumulation was greater after ingestion of the drink containing 32 g of 2H2O than after either of the other two drinks, and the 2H accumulation rate was greater after ingestion of the drink containing 16 g of 2H2O than after the drink containing 8 g of 2H2O. When data from all three experiments were combined, significant correlations were observed between the rate of accumulation of 2H in the circulation (p.p.m. min−1) and the amount (rs= 0.75, P < 0.001) and concentration (rs= 0.69, P < 0.001) of 2H2O in the test drink, but there was no relationship (rs= 0.09, P= 0.5) between the rate of 2H accumulation in the blood and the volume of the drink consumed. The results suggest that the rate of tracer accumulation in the blood after ingestion of different volumes of test drinks is not a reliable indication of the availability of the ingested fluid, but that the method gives at least a qualitative measure of the sum of the effects of gastric emptying and intestinal water absorption.
Blockage of Mouse Muscle Nicotinic Receptors by Serotonergic Compounds
Authors: García‐Colunga Jesús , Miledi Ricardo 
Published: May 2004

SUMMARYXenopus laevis oocytes were used to analyse the effects of serotonin (5‐hydroxytryptamine, 5‐HT) and serotonergic agents on ionic currents elicited by the activation of mammalian muscle nicotinic acetylcholine receptors (AChRs). 5‐HT as well as other serotonergic agents, such as ketanserin, 8‐hydroxy‐2‐(di‐n‐propylamino)tetralin (8‐OH‐DPAT), methysergide, spiperone, or fluoxetine alone (up to 1 mM), did not elicit membrane currents in Xenopus oocytes expressing AChRs, but they reversibly reduced the current elicited by acetylcholine (ACh‐current). Serotonin was applied before, together with or after ACh application, and its effects were examined on desensitizing and non‐desensitizing ACh‐currents. 5‐HT reduced the amplitude and accelerated the desensitization of the desensitizing currents. In contrast, non‐desensitizing currents were reduced in amplitude but their time course was not significantly affected. With the same concentration of 5‐HT the inhibition was stronger on desensitizing than on non‐desensitizing ACh‐currents. For example, 100 μM 5‐HT reduced the peak of a desensitizing ACh‐current to 0·48 ± 0·06 (peak current ratio) and after 40 s the current was reduced to a ratio of 0·25 ± 0·04, whereas a non‐desensitizing ACh‐current was reduced to a ratio of 0·66 ± 0·01. All the serotonergic agents tested inhibited the ACh‐currents rapidly and reversibly, suggesting that they are acting directly on the AChRs. The half‐inhibitory concentration, IC50, of 5‐HT acting on non‐desensitizing currents elicited by 250 nM ACh was 247 ± 26 μM and the Hill coefficient was [sim]0.88, suggesting a single site for the interaction of 5‐HT with the receptor. It appears that 5‐HT inhibits AChRs non‐competitively because neither the half‐effective concentration of ACh, EC50, for ACh‐current nor the Hill coefficient were affected by 5‐HT. Furthermore, the extent of inhibition of 5‐HT on AChRs did not depend on the nicotinic agonist (suberyldicholine, ACh or nicotine). The inhibition of AChRs by serotonergic agents was voltage‐dependent. The electrical distance of the binding site for 5‐HT was [sim]0.75, whereas for the other serotonergic agents tested it was [sim]0.22, suggesting that ketanserin, 8‐OH‐DPAT, methysergide, spiperone and fluoxetine act within the ion channel, but at a site more external than that for 5‐HT. These substances inhibited the ACh‐current more potently than 5‐HT. We conclude that 5‐HT and serotonergic agents inhibit, in a non‐competitive manner, the ACh‐current in muscle AChRs by blocking the open receptor‐channel complex. Moreover, 5‐HT appears to promote the desensitized state of the receptor when the current is elicited by high ACh concentrations.
Effects of Skin Surface Cooling and Heating on Autonomic Nervous Activity and Baroreflex Sensitivity in Humans
Authors: Kinugasa Hideki , Hirayanagi Kaname 
Published: May 2004

SUMMARYThe influence of skin surface cooling and heating on heart rate variability (HRV), blood pressure variability (BPV), and baroreflex sensitivity (BRS) were studied in 11 healthy supine volunteers in air temperatures of 18°C (cool), 24°C (mild), 48°C (warm), and 60°C (hot) in a styrene foam chamber. The high‐frequency component of HRV (HFRR) decreased and the ratio of low‐ to high‐frequency components, LFRR/HFRR, increased with skin surface heating. Therefore, a suppression of cardiac vagal nervous activity and an enhancement of cardiac sympathetic nervous activity can be caused by skin surface heating. The low‐frequency component of BPV (LFSBP), i.e. the fluctuations of the Mayer waves, increased with skin surface heating. The responses between the very low‐frequency components of HRV (VLFRR) and systolic BPV (VLFSBP) to thermal skin stimulation were different, although these variables both were considered to be indicators of the thermoregulatory vasomotor control or renin‐angiotensin system. Baroreflex sensitivity (BRS) did not increase with skin surface heating, at least in humans.
Effect of Hypocalcaemia on Glucose Metabolism in Hyperketonaemic Piglets
Authors: Schlumbohm C. , Harmeyer J. 
Published: May 2004

SUMMARYIn nine 2‐ to 3‐month‐old hyperketonaemic piglets the kinetics of glucose and d‐β‐hydroxybutyrate (d‐BHB) metabolism were studied during hypo‐ and normocalcaemia in paired experiments. Hyperketonaemia (1·3 and 2·5 mmol d‐BHB (l plasma)‐1) was generated by a stepwise increase of dl‐BHB infusion. Hypocalcaemia spontaneously developed in five piglets due to an inherited calcitriol deficiency and was induced in four control piglets by a continuous infusion of Na2‐EDTA. The method of single isotopic marker injections of glucose and d‐BHB was used to calculate replacement rates, rate constants and half‐lives of glucose and d‐BHB in plasma. When DL‐BHB was infused at the same rate into normo‐ and hypocalcaemic piglets, hypocalcaemia reduced the rate constant of glucose by 20‐30% and the replacement rate of glucose by 34%. In the presence of hyperketonaemia, hypocalcaemia increased the rate of replacement of d‐BHB by 6‐40%. The replacement rate represents the sum of endogenous production and the rate of DL‐BHB infusion. This observation shows that the endogenous production of d‐BHB was higher during hypocalcaemia than during normocalcaemia.
The Effects of in Vivo Pulmonary Oxygenation on Lung Liquid Production in Near‐Term Fetal Sheep
Authors: Round J. E. C. , Junor R. W. J. , Gallagher M. E. , Walters D. V. 
Published: May 2004

SUMMARYLung liquid (LL) is secreted into the fetal lung lumen, but it must be rapidly absorbed at birth to allow air breathing. In vitro studies have implicated oxygen as a possible factor causing the switch from secretion to absorption of lung liquid at birth. We developed a technique of oxygenating the fetal lung using liquid ventilation with haemoglobin (Hb) solutions in chronically catheterized fetal lambs (129‐140 days gestation; term, 147 days). In some experiments 2,3‐diphosphoglycerate (DPG) was added to increase oxygen delivery. LL secretion rate (Jv) was measured using an indicator dilution method. Eighteen fetuses were divided into four groups and ventilated with liquid under the following conditions: (i) Hb with oxygen, (ii) Hb without oxygen, (iii) Hb with DPG and oxygen and (iv) Hb with DPG without oxygen. There was a significant rise (2·6 mmHg, P < 0·02) in fetal arterial PO2 in group iii, but in none of the other groups. In the first 3 h of liquid ventilation there was no difference in Jv between the groups. In group i, during hours 4‐6 of liquid ventilation, there was a significant rise in secretion rate from 2·25 ± 0·88 to 3·74 ± 0·85 ml h−1 kg−1 (P < 0·001). In group iii, when comparing Jv in the first 3 h of liquid ventilation with that in the following 3 h period of liquid ventilation, a strong trend towards reduction in secretion was observed, falling from 3·03 ± 0·65 to 0·74 ± 0·92 ml h−1 kg−1 (three of the four experiments showed a significant decrease in Jv in hours 4‐6). These experiments indicate that oxygen delivered to the fetus using liquid ventilation with haemoglobin solutions leads to increased LL secretion when oxygen delivery is small, and suggest there is a decrease in secretion with greater oxygen delivery to the lung.
H+‐Zwitterionic Amino Acid Symport at the Brush‐Border Membrane of Human Intestinal Epithelial (Caco‐2) Cells
Authors: Thwaites David T. , Stevens Beverley C. 
Published: May 2004

SUMMARYTransport of a number of dipolar amino acids (and the orally active antibiotic D‐cycloserine) across the apical membrane of human intestinal epithelial (Caco‐2) cell monolayers is mediated by a Na+‐independent, pH‐dependent transport mechanism. Relatively little is known about the mode of action of this transport system so to differentiate between pH dependence and proton coupling three experimental protocols were designed and tested. The results demonstrate, firstly, that it is the transapical pH gradient and its maintenance (rather than apical acidity alone) that is important in amino acid uptake. Secondly, Na+‐independent uptake of seven dipolar amino acids (with pKa (‐log of acid dissociation constant) values between 1.50 and 4.23) showed a similar dependence on apical pH (half‐maximal uptake being observed at pH 5.99‐6.20). Thirdly, the pattern of pH‐dependent amino acid (β‐alanine) uptake is similar irrespective of whether the cationic substrate concentration is varied or constant, demonstrating no relationship between uptake and concentration of the cationic form of the amino acid. These observations demonstrate that the transport mechanism is a H+‐zwitterionic amino acid symporter and suggest that the presence of a H+ gradient at the apical surface of the human small intestine (in the form of the acid microclimate) may be important in driving nutrient absorption.
The Effect of Stimulation Frequency on Blood Flow in Rat Fast Skeletal Muscles
Authors: Hawker M. J. , Egginton S. 
Published: May 2004

SUMMARYThe effect of stimulation frequency on intact muscle blood flow was measured by radiolabelled microsphere entrapment. Maximum flow occurred at 4 Hz in both extensor digitorum longus and tibialis anterior (156 ± 13 and 205 ± 24 ml min−1 (100 g)−1, respectively). Regional differences in fibre composition were reflected in the relative flow rates, with functional hyperaemia in the oxidative tibialis anterior core being twice that of the glycolytic cortex at 10 Hz. A consistent difference in flow between legs was noted that may originate from an unequal division of the common iliac artery in rats.
Anaerobic Power of the Arms and Legs of Young and Older Men
Authors: Marsh G. D. , Paterson D. H. , Govindasamy D. , Cunningham D. A. 
Published: May 2004

SUMMARYThe purpose of this study was to examine differences in the anaerobic exercise performance of young and older men. Eight healthy, active older (68.5 ± 2.4 years old, mean ±s.d.) and eight healthy, active young (30.6 ± 4.5 years old) subjects were assessed for peak and mean power output (PP and MP, respectively) of the legs and arms, during 30 s Wingate tests. PP during leg exercise was significantly (P < 0.05) higher in the young (14.6 ± 1.6 W kg−1) compared with the older (10.7 ± 1.0 W kg−1) group. MP of the legs was also greater in the young subjects (10.7 ± 0.7 vs. 7.4 ± 0.9 W kg−1). These differences in PP and MP remained significant when expressed relative to lean leg volume. PP during arm cranking was significantly greater in the young subjects (8.9 ± 0.7 vs. 7.5 ± 0.6 W kg−1) as was MP (6.4 ± 0.7 vs. 5.0 ± 0.7 W kg−1). Post‐exercise blood lactate concentration in the older group (7.0 ± 1.6 mmol l−1) was less (P < 0.05) than in the young group (10.6 ± 2.0 mmol l−1), for leg work only. The significant loss of anaerobic power in the older group could not be explained by a difference in muscle mass. Power output was also lower in the arms, but to a lesser extent. The results of this study suggest that a reduction in the ability to perform high intensity exercise may be an inevitable consequence of ageing. The extent, however, of this decline varies with different muscle groups.
Cardiovascular Changes Associated with Dehydration and Drinking in Unrestrained, Lactating Goats
Authors: Olsson Kerstin , Carlsson Erika 
Published: May 2004

SUMMARYThe aim of this study was to investigate if the alertness connected with seeing water increased arterial blood pressure and heart rate to the same extent as the act of drinking, and if ingestion of warm water caused a different effect compared with ingestion of cool water on these cardiovascular variables. Seven goats of the Swedish domestic breed (Capra hircus) were used in a cross‐over design. The animals were dehydrated for 24 h. They were allowed to watch water being prepared for 11‐16 min, after which they were given access to warm (35°C) or cool (15°C) water. The goats drank 6.86 ± 0.36 l of the warm water and 4.54 ± 0.35 l of the cool water (P < 0.05) within the first hour. The arterial blood pressure, heart rate and activity of the animals were registered by an implanted telemetric device. Dehydration did not affect the cardiovascular variables, except before feeding in the morning, when the heart rate accelerated faster in dehydrated goats. Heart rate increased abruptly when dehydrated goats saw water being prepared, remained at the increased level during drinking and then slowly declined. It increased again during the afternoon feeding, to a level similar to that on control days, but between 18.00 and 06.00 h the heart rate was higher than during control nights. Blood pressure did not change when the goats saw water, but increased when they drank. On the morning following rehydration, the rise in heart rate in response to feeding was delayed compared with that during control and dehydration periods. It is concluded that seeing water caused arousal in the goats, resulting in an accelerated heart rate. The additional rise in blood pressure during the act of drinking appears to be a combination of excitement and sensory inputs from the pharyngeal region, causing a temporary activation of the sympathetic nervous system.