bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Skin Surface Cooling and Heating on Autonomic Nervous Activity and Baroreflex Sensitivity in Humans
Authors: Kinugasa Hideki , Hirayanagi Kaname
Published: May 2004

The 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

In 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

Lung 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

Transport 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

The 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

The 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

The 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.
Pancreatic α Cell Function in the Fetal Foal During Late Gestation
Authors: Fowden A. L. , Forhead A. J. , Bloomfield M. , Taylor P. M. , Silver M.
Published: May 2004

Plasma glucagon concentrations were measured in chronically catheterized fetal ponies and their mothers between 260 days of gestation and term (≈ 335 days). Fetal α cell responses to arginine and variations in fetal glycaemia were also examined during late gestation. Immunoreactive glucagon was present in fetal plasma at 260 days of gestation and its concentration in utero increased after 320 days and then again at birth. Maternal plasma glucagon concentrations were higher after 300 days than earlier in gestation but were lower than the corresponding fetal value throughout the period of gestation studied. Fetal α cells responded rapidly to intravenous arginine infusion but not to changes in the fetal glucose level induced by maternal fasting for 36 h or by intrafetal infusion of glucose. The maximal increment in fetal plasma glucagon in response to arginine occurred at the end of the 5 min infusion and was positively correlated to the basal pre‐infusion plasma glucagon concentrations. Fetal plasma glucagon concentrations were unaffected by either hyper‐ or hypoglycaemia. In contrast, maternal plasma glucagon levels were significantly increased by fasting. These observations indicate that equine pancreatic α cells are functional in utero but that they are unresponsive to variations in glycaemia until after birth.
Laryngeal Movements During the Respiratory Cycle Measured with an Endoscopic Imaging Technique in the Conscious Horse at Rest
Authors: Lafortuna Claudio L. , Albertini Mariangela , Ferrucci Francesco , Zucca Enrica , Braghieri Martina , Clement M. Giovanna , Saibene Franco
Published: May 2004

A video‐laryngoscopic method, implemented with an algorithm for the correction of the deformation inherent in the endoscope optical system, has been used to measure the dorsoventral diameter (Drg) and the cross‐sectional area (CSArg) of the rima glottidis in five healthy workhorses during conscious breathing at rest. Simultaneous recording of the respiratory airflow was also obtained in two horses. Drg measured 82·7 ± 4·5 mm (mean ±s.d.) independently of the respiratory phase, and did not differ from the measurement in post‐mortem anatomical specimens of the same horses. CSArg ranged from 1130 ± 117 mm2 (mean ±s.d.) during the inspiratory phase to 640 ± 242 mm2 during the expiratory phase, being always narrower than tracheal cross‐sectional area, which was 1616 ± 224 mm2, as determined from anatomical specimens. Both inspiratory and expiratory airflow waves displayed a biphasic pattern. Maximal laryngeal opening occurred in phase with the second inspiratory peak, while during expiration CSArg attained a minimum value during the first expiratory peak which was significantly smaller (P < 0·01) than the area subsequently maintained during the rest of the expiratiory phase. These quantitative measurements of equine laryngeal movements substantiate the important role played by the larynx in regulating upper airway respiratory resistance and the expiratory airflow pattern at rest.
Development of the Fluorescent Microsphere Technique for Quantifying Regional Blood Flow in Small Mammals
Authors: Deveci D. , Egginton S.
Published: May 2004

Tissues weighing from 0·006 to 3·0 g were dissected and put directly into 15 ml screw cap polypropylene tubes with a conical base (maximum of 3 g per tube). It proved unnecessary to mince tissue, even though smaller pieces may aid quicker digestion. Five millilitres of 2 M KOH in 99 % (IMS) ethanol with 0·5 % Tween‐80 was then added. Tissue digestion was usually completed in 2‐4 h using a dry heating block held at 60°C, with intermittent shaking. Samples were routinely processed using fresh tissues, although storage of frozen tissue (in the dark at ‐20°C) introduced no detectable error in BF estimation and tended to aid tissue maceration.

After digestion was completed the tubes were centrifuged at 3000 r.p.m. (1500 g) for 15 min.

The supernatant was carefully aspirated until < 500 μl was left, thereby reducing the possibility of accidental loss of microspheres.

After 1 ml dH2O was added the tubes were quickly vortexed to prevent microsphere flocculation and aid resuspension of remaining pellets, while the subsequent addition of ethanoic Tween (100 % ethanol + 0·5 % Tween‐80) allowed complete sedimentation by centrifugation.

Nine millilitres of ethanoic Tween‐80 was added, and the tubes were vortexed and spun at 1500 g for 15 min.

The supernatant was aspirated as above (Step 3).

Five millilitres of 100 mM phosphate buffer (pH 7·00) was added to neutralize the pellet as alkaline solutions quench fluorescence. Using aqueous solutions increased the possibility of microsphere loss by adhesion to the surface of tubes or aggregation, which could readily be seen by eye when tubes were examined under bright light, and hence the buffer was followed by addition of 4 ml absolute ethanol and further vortexing, before spinning (1500 g) for 20 min.

The supernatant was aspirated, leaving up to 300 μl depending on the amount of tissue residue, and the remaining microspheres and pellet were quickly vortexed to ensure complete resuspension.

The tubes were left to evaporate in an oven at 60°C and then briefly vortexed during this period to disperse more of the flocculent, until around 100 μl fluid remained. This improves solvent extraction of microspheres, which may be less efficient in a completely dry pellet.

Two or three millilitres of solvent (di(ethylene glycol) ethyl ether acetate, 98 %; Aldrich Chemical Co., Poole, Dorset, UK) was added according to the expected fluorescence intensity, and vortexed several times over 3‐5 min. After 30 min the tubes were sonicated in a water bath for 5 min to complete dye extraction by the solvent. The tubes were kept as far as possible in the dark after the solvent was added to avoid photo‐bleaching of the fluorescent dyes.

After sonication, the tubes were occasionally spun (1500 g) once more to sediment any undigested/undissolved material, though this was rarely necessary in our experiments. Readings should be completed within 1 h to avoid loss of signal intensity.
Role of Nitric Oxide Synthase and Cyclooxygenase in Pulmonary Vascular Control in Isolated Perfused Lungs of Ferrets, Rats and Rabbits
Authors: Liu Xia , Bee Denise , Barer Gwenda R.
Published: May 2004

Dilator products of nitric oxide synthase (NOS) and cyclooxygenase (COX) may contribute to the low normal pulmonary artery pressure (Ppa). In isolated perfused lungs of ferrets, rabbits and rats we investigated this hypothesis by blockade of NOS with L‐NAME (L‐nitro‐arginine methyl ester) and COX with meclofenamate. There were species differences. Inhibition of either enzyme caused little rise in Ppa in ferrets and rats but inhibition of both enzymes caused huge increases in Ppa. We suggest this might be due to intracellular connections between the excitatory pathways for NOS and COX dilators, such that inhibition of one enzyme leads to activation of the other. Impairment of these endothelial‐based enzymes in pulmonary vascular disease might lead to severe pulmonary hypertension. By contrast, in rabbits, comparable doses of L‐NAME lead to large rises in Ppa which were reversed rather than amplified by COX blockade. NO seems to protect against some pressor/oedema forming product of COX in this species.
Inhibition of Mucosal Glycylsarcosine Uptake by Acetate in Rat Distal Small Intestine
Authors: Scharrer E. , Amstutz I. , Grenacher B.
Published: May 2004

Acetate deriving from microbial fermentation may occur at considerable concentrations in the distal small intestine, where it appears to be absorbed by two different mechanisms: acetate‐HCO3− exchange and non‐ionic diffusion. Whether acetate affects absorption of other nutrients at this intestinal site is not known. Therefore the influence of acetate (30 mmol l−1) on oligopeptide absorption was studied using an in vitro mucosal uptake technique allowing measurement of substrate uptake across the brush border membrane (BBM). Acetate significantly inhibited mucosal uptake of 14C‐labelled glycylsarcosine (Gly‐Sar) at pH 6 and pH 7 in the presence of sodium. No inhibition occurred in the absence of sodium. Both acetate and the absence of sodium decreased Vmax of mucosal Gly‐Sar uptake without substantially affecting the apparent Km value. Since it is well established that Vmax of peptide transport across the intestinal BBM depends on the size of the transmembrane H+ gradient as a driving force the present findings are in accordance with the assumption that acetate inhibits peptide absorption by attenuating the H+ gradient across the BBM, which depends on the presence of sodium.
Non‐Muscarinic and Non‐Nicotinic Inhibition by the Acetylcholine Analogue Carbachol of the Delayed Rectifier Potassium Current, ik, in Rabbit Isolated Sino‐Atrial Node Cells
Authors: Lei Ming , Kohl Peter , Brown Hilary , Noble Denis
Published: May 2004

The effect of carbachol, an analogue of acetylcholine, on the delayed rectifier potassium current, iK, was investigated in rabbit isolated sino‐atrial node cells using the whole cell patch clamp technique with amphotericin‐permeabilized patches. In the presence of 500 nM atropine and 500 nM hexamethonium to block muscarinic and nicotinic receptors, respectively, 500 nM carbachol decreased the amplitude and rate of deactivation of iK without, however, affecting the slope of the iK activation curve. The same concentration of carbachol decreased the pacemaking rate of spontaneously active sino‐atrial node cells by more than 13%. Thus, there is a non‐muscarinic and non‐nicotinic pathway for cholinergically induced reduction in the amplitude and rate of deactivation of iK that would appear to contribute to negative chronotropy in rabbit sino‐atrial node pacemaker cells.
Influence of Thyrotrophin‐Releasing Hormone on Thermoregulatory Adaptation after Birth in Near‐Term Lambs Delivered by Caesarean Section
Authors: Heasman Lindsay , Clarke Lynne , Symonds Michael E.
Published: May 2004

We investigated the hypothesis that exogenous stimulation with thyrotrophin‐releasing hormone (TRH) immediately prior to umbilical cord clamping can improve thermoregulatory adaptation after birth in near‐term lambs delivered by Caesarean section. Lambs received an umbilical vein injection of saline ± TRH (8 μg) prior to cord clamping. The rate of change in colonic temperature and oxygen consumption after birth were not influenced by TRH, but TRH‐treated lambs exhibited a greater incidence of shivering compared with controls over the first hour of neonatal life. Two and a half hours after birth, TRH‐treated lambs possessed brown adipose tissue (BAT) with a higher thermogenic activity (i.e. GDP binding to mitochondrial protein), but their BAT had a reduced DNA content and they had less hepatic glycogen than control lambs. TRH administration had no effect on iodothyronine 5′ deiodinase activity in BAT and liver, or on plasma concentrations of total triiodothyronine, thyroxine, cortisol or free fatty acids. Three TRH‐treated but no control lambs, failed to establish continuous breathing, so tissues from these treated lambs together with time‐matched controls were sampled 25 min after birth. These ‘non‐surviving’ TRH‐treated lambs had very high plasma catecholamine concentrations, but their lung weights were similar to controls. ‘Surviving’ TRH‐treated lambs possessed lungs with less DNA than non‐surviving TRH‐treated lambs. It is concluded that umbilical vein injection of TRH prior to umbilical cord clamping increases the recruitment of both shivering and non‐shivering thermogenesis after birth.
Measurement of Changes in Glomerular Filtration Rate Induced by Atrial Natriuretic Peptide in the Rat Kidney
Authors: Caron N. , Kramp R.
Published: May 2004

This study was undertaken to improve the measurement of glomerular filtration rate (GFR) during the acute diuretic phase induced by atrial natriuretic peptide (ANP), which may indeed alter the renal clearance of inulin (GFRCL) due to dead space error. A technique to measure GFR without urine collections was therefore developed in anaesthetized rats prepared as for micropuncture. To do so, arterial blood was periodically collected and renal venous blood was withdrawn simultaneously from a catheter inserted into the left suprarenal vein to determine the renal extraction coefficient of inulin (CEIN). In addition, renal blood flow (RBF) was continuously measured with an electromagnetic flow transducer fitted around the left renal artery to estimate renal plasma flow (RPF). GFR (GFRCE) was then calculated as the product of RPF and CEIN. To study the effects of ANP on GFR, rats were injected i.v. with 10 μl of saline without (n= 6; vehicle) or with 1 μg ANP (n= 6; ANP) and GFRCE and GFRCL were compared before and after each treatment. They did not differ significantly during baseline measurements in each experimental group and were not modified after vehicle. Similarly, RBF remained constant. In contrast, RBF and GFRCE increased rapidly and simultaneously 90 s after ANP, from 9·07 ± 0·25 to 10·07 ± 0·35 (12%) and from 1·209 ± 0·188 to 1·715 ± 0·190 ml min−1 (42%), respectively (P < 0·05). GFRCL increased to an even greater extent (88%). Moreover, the peak enhancement of GFRCL was delayed and occurred 180 s after ANP. The renal clearance of inulin was thus unduly elevated due to sudden changes in the dead space induced by the diuretic effect of ANP. In conclusion, determination of glomerular filtration rate by the method of renal extraction of inulin provided more reliable results than those achieved using the classical method of renal clearance of inulin. Moreover, it was sufficiently sensitive to detect small and transient changes in GFR induced by the injection of 1 μg ANP.
Chemoattractant‐ and Mitogen‐Induced Generation of Reactive Oxygen Species in Human Lymphocytes: The Role of Calcium
Authors: Orie Nelson N. , Zidek Walter , Tepel Martin
Published: May 2004

This study examined the role of calcium in the generation of reactive oxygen species (ROS) in human lymphocytes activated by the chemoattractant formyl‐Met‐Leu‐Phe (fMLP) and the T‐cell mitogen phytohaemagglutinin (PHA). The concentrations of cytosolic calcium ([Ca2+]i) and ROS were monitored simultaneously with a fluorescence spectrophotometer after the cells had been incubated in fura‐2 (calcium‐sensitive dye) and 2′,7′‐dichlorofluorescein diacetate (DCF‐DA, ROS‐sensitive dye). The lymphocytes were stimulated with fMLP (200 nmol l−1) or PHA (10 μmol l−1) in the absence and presence of extracellular calcium. A dose‐response test was also conducted for extracellular calcium. fMLP and PHA significantly increased both [Ca2+]i (P < 0.001) and ROS concentrations (P < 0.001) above the control levels in the presence of extracellular calcium. However, such increases were abolished in the absence of extracellular calcium, suggesting total dependence of the responses to both fMLP and PHA on transplasma‐membrane calcium influx. There were also graded increases in ROS with increasing concentrations of extracellular calcium. The results show that transplasma‐membrane calcium influx is essential for fMLP‐ and PHA‐induced generation of reactive oxygen species in human lymphocytes.
Oxygen Uptake Kinetics of Older Humans are Slowed with Age but are Unaffected by Hyperoxia
Authors: Bell C. , Paterson D. H. , Kowalchuk J. M. , Cunningham D. A.
Published: May 2004

Cross‐sectional studies have compared the oxygen uptake (VO2) kinetics during the on‐transient of moderate intensity exercise in older and younger adults. The slower values in the older adults may have been due to an age‐related reduction in the capacity for O2 transport or alternatively a reduced intramuscular oxidative capacity. We studied: (1) the effects of ageing on VO2 kinetics in older adults on two occasions 9 years apart, and (2) the effect of hyperoxia on VO2 kinetics at the second test time. After a 9 year period, follow‐up testing was undertaken on seven older adults (78 ± 5 years, mean ±s.d.). They each performed six repeats of 6 min bouts of constant‐load cycle exercise from loadless cycling to 80 % of their ventilatory threshold. They breathed one of two gas mixtures (euoxia: inspired O2 fraction, FI,O2, 0·21; hyperoxia: FI,O2, 0·70) on different trials determined on a random basis. Breath‐by‐breath VO2 data were time aligned and ensemble averaged. VO2 kinetics, modelled with a single exponential from phase 2 onset (+20 s) to steady state and described by the exponential time constant ([tau]) were compared with data collected from the same adults 9 years earlier. One‐way repeated measures analysis of variance revealed that [tau] was slowed significantly with age (from 30 ± 8 to 46 ± 10 s), but was unaffected by hyperoxia (43 ± 15 s). We concluded that: (1) in older adults studied longitudinally over a 9 year period, the on‐transient VO2 kinetics are slowed, in agreement with, but to a greater extent, than from cross‐sectional data; and (2) the phase 2 time constant ([tau]) for these older adults was not accelerated by hyperoxic breathing. Thus the expected hyperoxia‐induced increase in the capacity for O2 transport was not associated with faster on‐transient VO2 kinetics suggesting either that O2 transport may not limit VO2 kinetics during the 8th decade, or that O2 transport was not improved with hyperoxia.
Effects of Changes in pH and PCO2 on Wall Tension in Isolated Rat Intrapulmonary Arteries
Authors: Sweeney Michele , O'Regan Ronan G. , McLoughlin Paul
Published: May 2004

We examined mean (±s.e.m.) changes in wall tension in isolated rat intrapulmonary arteries on switching from control conditions (pH 7.38 ± 0.01; PCO2, 34.4 ± 0.5 mmHg) to hypercapnic acidosis (pH change, ‐0.24 ± 0.01; PCO2 change, +27.5 ± 0.9 mmHg), isohydric hypercapnia (pH change, ‐0.02 ± 0.01; PCO2 change, +28.5 ± 0.8 mmHg) and normocapnic acidosis (pH change, ‐0.24 ± 0.01; PCO2 change, ‐0.5 ± 0.3). Arteries were submaximally preconstricted with prostaglandin F2alpha; and changes in tension are expressed as a percentage of the 80 mM KCl‐induced contraction (%Po). Mean changes in wall tension on switching to hypercapnic acidosis (+4.4 ± 3.7%Po), isohydric hypercapnia (+1.9 ± 2.2%Po) and normocapnic acidosis (−1.5 ± 1.9%Po) were not significantly different from the change observed on switching to control conditions (+3.5 ± 1.1%Po), and were unaltered by endothelial removal. In isolated carotid preparations, the change in tension in isohydric hypercapnia (‐6.8 ± 7.1%Po) was not significantly different from that observed in control switches (+8.6 ± 3.2%Po). Significant reductions in tension (P < 0.001) were observed in hypercapnic (‐42.9 ± 7.8%Po) and normocapnic acidosis (‐36.4 ± 9.0%Po). These data suggest that intrapulmonary arteries are resistant to the vasodilator effects of extracellular acidosis observed in systemic (carotid) vessels.
Effect of Altered Body CO2 Stores on Pulmonary Gas Exchange Dynamics During Incremental Exercise in Humans
Authors: Ozcelik O. , Ward S. A. , Whipp B. J.
Published: May 2004

The lactate threshold is a widely used and, at times, controversial construct in exercise physiology and pathophysiology. Its non‐invasive estimation during incremental exercise depends upon CO2 output increasing as a function of O2 uptake, i.e. ‘V‐slope’, as a result of bicarbonate buffering during the lactic acidosis. However, we hypothesised that the V‐slope deflection could also occur as a consequence of metabolic CO2 being diverted proportionally more into the CO2 stores in the early phase of exercise. Eight healthy males performed two incremental exercise tests on a cycle ergometer, with and without controlled prior hyperventilation; the hyperventilation caused end‐tidal PCO2 to decline by [sim]10 mmHg, with the clearance of a CO2 volume averaging 2547 ml. This corresponded to an ‘effective’ CO2 capacitance of some 3·12 ml mmHg−1 kg−1. Gas exchange was determined breath‐by‐breath, and blood was sampled from the dorsum of the heated hand. Our results demonstrate that the early dynamics of CO2 wash‐in to the previously depleted body stores can result in a ‘pseudo‐threshold’, i.e. significantly before the onset of the actual lactic acidosis. Precautions should therefore be taken to avoid hyperventilation prior to non‐invasive estimation of the lactate threshold.
Pyrimidine Nucleotide‐Evoked Inhibition of Cyclic AMP Accumulation in Equine Epithelial Cells
Authors: Wilson Stuart M. , Gallagher Marie , Rakhit Soma , Remsbury Anna L. , Ko Wing Hung
Published: May 2004

Uridine triphosphate (UTP) evoked inhibition of adrenaline‐evoked cAMP accumulation in cultured equine epithelial cells (EC50, 1·8 ± 0·2 μM) and this effect was mimicked by 5‐Br‐UTP (EC50, 6·6 ± 1·8 μM) and uridine diphosphate (UDP; EC50, 96 ± 26 μM). This inhibitory action of UTP was abolished by pre‐treating cells with pertussis toxin (10 ng ml−1, 24 h). UTP (EC50, 2·3 ± 0·3 μM) and 5‐Br‐UTP (EC50, 29·4 ± 9·4 μM) also increased intracellular free calcium ([Ca2+]i) whilst UDP did not; the two effects are thus differentially sensitive to these pyrimidine nucleotides. ATP evoked cAMP accumulation in control cells and this response was unaffected by pertussis toxin. There is, therefore, no indication that ATP activates the pertussis toxin‐sensitive inhibitory pathway. The UTP‐evoked inhibition of cAMP accumulation was abolished by isobutylmethylxanthine (IBMX, 5 mM) and so the negative control over cAMP levels appears to be mediated by receptors that are selectively activated by pyrimidine nucleotides and permit control over phosphodiesterase activity.
Mechanical Properties of Smooth Muscle Portal Vein in Normal and Dystrophin‐Deficient (MDX) Mice
Authors: Mancinelli R. , Tonali P. , Romani R. , Tringali A. , Vargiu R. , Azzena G. B.
Published: May 2004

Mechanical properties of the vascular smooth muscle from normal and dystrophin‐deficient (mdx) mice were examined. Changes in resting and developed tensions in response to stretch were recorded in isolated portal vein. The vascular segments were elongated in 5% increments of the ‘in situ’ length (Lr) up to 1·30Lr. The resting length‐tension curves in male mdxmice were similar to normal mice, while a marked decrease in the slope of the curve was noted in female mdx mice. These findings were not affected by atropine, phentolamine, tetrodotoxin or [Ca2+] in the surrounding media. At Lr, the tension of isolated portal vein was characterized by spontaneous synchronized uniform force waves in normal mouse. In contrast, in mdxmouse portal veins an irregular motor pattern characterized by desynchronized force waves with a decrease of amplitude and an increase in frequency was recorded. Extension of the length of the portal vein segment did not increase the spontaneous phasic activity developed in female mdx mice although this was noted with male mdx mice and normal mice. Experiments with chemical depolarizing agents indicated that spontaneous myogenic excitation activated the great majority of vascular smooth muscle cells in normal mouse portal vein, whereas in mdx mice only a reduced number of these cells were excited suggesting that in the mdx mouse the intercellular electronic coupling is altered. In conclusion this study provides the first description of the mechanical activities of portal vein longitudinal muscle and shows that in mdx mice the motor activity is severely disrupted.
Effects of Reducing Submandibular Blood Flow on Secretory Responses to Parasympathetic Stimulation in Anaesthetized Cats
Authors: Hanna S. J. , Brelen M. E. , Edwards A. V.
Published: May 2004

Submandibular secretory responses to stimulation of the parasympathetic chorda‐lingual nerve were investigated in five anaesthetized cats before, during and after withdrawal of blood (ca 20 ml kg−1) in order to investigate the consequences of a reduced blood flow through the gland. Stimulation at different frequencies (2, 4, 6 and 8 Hz) evoked a frequency‐dependent increase in the flow of submandibular saliva, sodium concentration, electrolyte and protein output. When the blood pressure was reduced (by about 50%) there was a significant reduction in submandibular blood flow and the secretion of both saliva and protein during stimulation. Under each set of conditions the flow of saliva was linearly related to the blood flow through the gland. It is concluded that submandibular secretory responses to electrical stimulation of the parasympathetic innervation can be significantly attenuated when the blood flow through the gland is reduced under the conditions employed in this study.
Vagotomy Suppresses Cephalic Phase Insulin Release in Sheep
Authors: Herath C. B. , Reynolds G. W. , Mackenzie D. D. S. , Davis S. R. , Harris P. M.
Published: May 2004

The effect of selective vagotomy of the abomasum, pylorus, duodenum and liver on insulin release during the cephalic phase of digestion was investigated in wethers and lactating ewes. Electrical stimulation of the cervical vagus nerves was carried out to test the completeness of the vagotomies performed. In experiment 1, using wethers, the abomasal, pyloric and duodenal branches (ADV; n= 7) or the hepatic, abomasal, pyloric and duodenal branches (HADV; n= 10) of the ventral and/or dorsal vagus nerves were cut; a third group of wethers underwent sham‐operation (SO; n= 8). In experiment 2, vagotomy (ADV; n= 5) or sham‐operations (SO; n= 5) were carried out in lactating ewes. Jugular blood was drawn before and after presentation of food for glucose and insulin determination (experiments 1 and 2) or before, during and after the electrical stimulation of the peripheral ends of the cut cervical vagus nerves in randomly selected lactating ewes (experiment 3: ADV = 3, SO = 3) and wethers (experiment 4: ADV = 4, HADV = 4, SO = 4), for determination of insulin only. Presentation of food caused an immediate and significant (P < 0.05) rise in plasma insulin levels in SO animals compared with ADV or HADV wethers (experiment 1) or ADV ewes (experiment 2) without any significant change in blood glucose concentrations. In comparison with the SO group the baseline‐corrected areas under the insulin response curve were significantly (P < 0.05) smaller for the respective vagotomized groups for periods 1‐2, 2‐4 and 4‐6 min (experiment 1) and 1‐2 and 2‐4 min (experiment 2) after presentation of food. Total area under the response curve for 10 min was significantly (P < 0.05) lower (experiment 1) and tended (P < 0.10) to be lower (experiment 2) for the vagotomized groups compared with that of the control groups. Direct electrical stimulation of the cervical vagus nerves raised plasma insulin concentrations to significantly (P < 0.05) higher levels in the SO ewes but not in the ADV ewes (experiment 3). It was also evident that in experiment 1, HADV did not have any additive effect over that achieved by ADV alone. These results indicate that the vagal innervation of the gut mediates insulin release during the cephalic phase of feeding in sheep. It is concluded that insulin secretion from the pancreatic β‐cells in response to either food‐related reflex activation of the vagal nuclei in the hypothalamus or direct cervical vagus nerve stimulation is mediated through the vagal efferent fibres carried in the abomasal, pyloric and duodenal branches of the vagus nerves in sheep.
L‐Arginine Transport at the Fetal Side of Human Placenta: Effect of Aspirin in Pregnancy
Authors: Acevedo C. G. , Rojas S. , Bravo I.
Published: May 2004

l‐Arginine transport by the fetal side of human placenta was investigated through the characterization of l‐[3H]arginine uptake in isolated perfused cotyledon. Competitive inhibition experiments suggest the presence of at least two transport systems: a Na+‐independent, pH‐insensitive system inhibitable by cationic amino acids, similar to system y+, and a Na+‐dependent system which recognizes both cationic and neutral amino acids only in the presence of Na+, i.e. a Bo,+‐like system. The kinetic analysis of l‐arginine uptake in the presence of Na+ revealed that the process is mediated by saturable components: a high‐affinity system (Km= 167 ± 18.0 μM; Vmax= 0.174 ± 0.012 μmol min−1) and a low‐affinity carrier (Km= 980 ± 112 μM; Vmax= 1.60 ± 0.12 μmol min−1). In the absence of Na+, l‐arginine uptake was fitted by one model with a Michaelis‐Menten constant of 200 ± 24.8 μM. These results suggest that the high‐affinity component corresponds to the Na+‐independent system y+, whilst the low‐affinity system may represent the activity of the Na+‐dependent Bo,+ transporter. Kinetic studies in placentae taken from aspirin‐treated pregnancies showed that l‐arginine is transported with a significantly higher affinity (Km= 42.5 ± 5.7 μM), but with a lower capacity (Vmax= 0.064 ± 0.003 μmol min−1) than in the non‐treated group. The latter finding suggests that aspirin would facilitate the uptake of the NO precursor only at very low arginine concentrations.
Effects on L‐Type Calcium Current of Agents Interfering with the Cytoskeleton of Isolated Guinea‐Pig Ventricular Myocytes
Authors: Pascarel Caroline , Brette Fabien , Cazorla Olivier , Le Guennec Jean‐Yves
Published: May 2004

We studied the effects of an external acute 10 min application of cytoskeletal interfering agents on cardiac L‐type calcium current (ICa,L). We found that colchicine, taxol and cytochalasin D had no direct effect on the L‐type calcium channel as indicated by the absence of effect on voltage‐dependent parameters. Phalloidin induced a shift in the I‐V curve which renders it difficult to use in excitation‐contraction coupling studies. Microfilaments of actin did not seem to regulate cardiac ICa,L as indicated by the lack of effect of cytochalasin D on ICa,L amplitude and inactivation kinetics. On the contrary, microtubules seem to be involved in the calcium‐dependent inactivation of ICa,L. This involvement might be direct, i.e. a physical link between the microtubules and some part of the channel protein, or it could be indirect, i.e. the calcium chelating properties and physical obstacle of microtubules in the space between the sarcolemma and the SR.
The Integrated Response to Hypoxia: From Circulation to Cells
Authors: Marshall Janice M.
Published: May 2004

I guess everyone who is asked to give one of the Physiological Society's Prize Lectures feels honoured, but I feel particularly honoured to have been asked to give the Joan Mott Prize Lecture. I first met Joan Mott in 1980 at the Oxford meeting of the Physiological Society. I had just given a communication on baro‐ and chemoreceptor influences on the cardiovascular system and she came to introduce herself to me. I was a young lecturer at the time, and still felt a rather junior member of the Society. I had seen Joan Mott at many Physiological Society meetings. I had heard her give communications and had heard her entering into lively discussions after papers, and I knew she was a well respected scientist. I was therefore flattered that she should have come to talk to me about my work. After that we met at many Physiological Society meetings and she always made a point of asking how our research was going and we would talk of common interests. To me this is one of the most important aspects of Physiological Society meetings, that young and older members of the Society can rub shoulders with one a nother and discuss science openly with no barriers. Joan Mott had an influence on me that I have tried to remember as I have become a more senior member of the Society.
Training‐Induced Alterations in Lactate Dehydrogenase Reaction Kinetics in Rats: A Re‐Examination
Authors: Favero Terence G. , Stavrianea Stasinos S , Klug Gary A.
Published: May 2004

The kinetics and the isozyme composition of lactate dehydrogenase (LDH) were measured in rat plantaris muscle during a 26 week endurance‐training program. Alterations in the LDH isozyme pattern were detectable after 6 weeks as the percentage of the M4 isozyme was reduced from 89 to 76% and the total percentage of M subunits compared with H subunits declined by 8%. At 16 weeks, M4 accounted for only 62% of the total. The replacement of M with H subunits continued when training was prolonged as M4 represented only 52% of the total isozymes at 26 weeks. Conversely, training for 6 and 16 weeks produced no changes in either Vmax or Km. At 26 weeks, these values declined for both the forward (pyruvate to lactate) and backward reactions. The rate constants for both reactions were also reduced. These data suggest that changes in LDH isozyme pattern do not contribute significantly to the enhancement of lactate oxidation that may occur after training. They also suggest that the functional significance of alterations in LDH structure and/or function are best determined from analysis of the overall reaction kinetics as opposed to individual characteristics such as the isozyme pattern, Km or Vmax.
Ion Currents in Smooth Muscle Cells from Human Small Bronchioles: Presence of an Inward Rectifier K+ Current and Three Types of Large Conductance K+ Channel
Authors: Snetkov V. A. , Ward J. P. T.
Published: May 2004

Bronchoconstriction of small bronchioles plays a major role in the increase in airway resistance following agonist challenge. There is evidence that the airway smooth muscle (ASM) of small bronchioles differs functionally from that in larger airways. Little is known however about the electrophysiology of small bronchioles. Ion currents were therefore studied in airway smooth muscle cells freshly dissociated from human intralobular bronchioles, with a diameter between 0·3 and 1·0 mm. As previously reported for human large airways, the major outward current in these cells was due to activity of large conductance K+ (BK) channels, with a relatively minor component due to a voltage‐gated delayed rectifier current (IDR), which was only observed in ∼30% of cells. Three distinct types of iberiotoxin‐ and TEA‐sensitive large conductance K+ channel contributed to large conductance K+ current (IBK). These included a highly voltage‐ and Ca2+‐sensitive 200 pS channel previously reported in human large airways, and two smaller channels of 150 and 100 pS previously seen only in human fetal or cultured ASM. In contrast to large airways, ASM cells from bronchioles also demonstrated a voltage‐gated inward rectifier current (IIR). IIR was activated by hyperpolarisation below the K+ equilibrium potential and could be blocked by submillimolar concentrations of Cs+ or Ba2+, and partially by physiological concentrations of Na+. Corresponding single channels with a conductance of ∼17 pS could also be recorded in the cell‐attached configuration. A small voltage‐independent current was also observed which was resistant to classic K+ and Cl− channel blockers but which could be abolished by replacement of Na+ with the impermeant cation N‐methyl‐D‐glucamine (NMDG+). Corresponding non‐selective single channels of ∼20 pS could be seen in inside‐out mode. These results demonstrate that ASM from small bronchioles differs in terms of ion currents and channels from ASM derived from large airways, with possible implications for function.
Inhibition of Baroreflex Vagal Bradycardia by Selective Stimulation of Arterial Chemoreceptors in Rats
Authors: Murata Tomohiro , Otsu Kazuya , Kobayashi Masayoshi , Nosaka Shoichiro
Published: May 2004

We reported recently that hypoxia inhibits baroreflex vagal bradycardia (BVB) in rats and that this inhibition persists following chemoreceptor denervation. However, since it is possible that hypoxia also affects the central processing of chemoreceptive input, the existence of chemoreceptor‐mediated inhibition of BVB cannot be ruled out. Therefore, we have studied whether selective chemoreceptor activation affects BVB in normoxic conditions. In pentobarbital‐urethane‐anaesthetized, succinylcholine‐immobilized, artificially ventilated rats, BVB was provoked by electrical stimulation of the aortic depressor nerve. Arterial chemoreceptors were selectively activated by intracarotid injection of a minute amount of sodium cyanide. Cyanide injection consistently increased blood pressure while changing heart rate variably. BVB was inhibited in a dose‐dependent manner. This inhibition, as well as changes in blood pressure and heart rate, was abolished following transection of the carotid sinus nerve (CSN) ipsilateral to the injection. Spinal cord transection at the C2 level did not affect the inhibition. On the other hand, intracarotid cyanide had no effect on bradycardia elicited by electrical stimulation of a peripheral cut end of the cervical vagus nerve. We conclude that chemoreceptor activation definitely inhibits BVB and that this inhibition is mediated by the CSN, and predominantly occurs in the central nervous system. The possibility is suggested that severe hypoxia suppresses not only BVB but also the chemoreceptor‐mediated inhibition of BVB, both via the direct, central action.