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.

In the vagally intact anaesthetised dog, we have investigated the role of nitric oxide (NO) on a normal sinus arrhythmia using an inhibitor of neuronally released NO, 1-(2-trifluoromethylphenyl) imidazole (TRIM). The mean and S.D. of the R-R interval was used to describe mean heart rate and heart rate variability, respectively. TRIM (0.8 mg I.C.) injected into the sinus node artery increased the mean heart rate slightly but reduced heart rate variability 3-fold from a control of 790 ± 124 ms (mean ± S.D.; n = 5) to 666 ± 36 ms (P < 0.01 Student's paired t test, n = 5). These results suggest that neuronally released NO may have a vagal facilitatory role in the maintenance of sinus arrhythmia in the normal heart. Experimental Physiology (2001) 86.5, 539-541.

We report the first simultaneous measurements of pHi, [Ca2+]i and tension, upon alteration of pHi, in isolated rat mesenteric arteries loaded with both carboxy SNARF and indo-1. In these vessels (pre-contracted by 30 mM KCl) alterations of pHi, by addition and subsequent washout of weak bases, produced complicated effects on tone. Although the changes in contractility did not mirror the changes in pHi they were, at all times, accompanied by parallel changes in [Ca2+]i. Experimental Physiology (2000) 85.3, 349-351.

The purpose of this study was to describe the influence of body size and sex on the decline in maximum oxygen uptake (O2,max) in older men and women. A stratified random sample of 152 men and 146 women, aged 55-86 years, was drawn from the study population. Influence of age on O2,max, independent of differences in body mass (BM) or fat-free mass (FFM), was investigated using the following allometric model: O2,max = BMb (or FFMb) exp(a + (c ' age) + (d ' sex)) [epsilon]. The model was linearised and parameters identified using standard multiple regression. The BM model explained 68.8 % of the variance in O2,max. The parameters (± s.e.e., standard error of the estimate) for lnBM (0.563 ± 0.070), age (-0.0154 ± 0.0012), sex (0.242 ± 0.024) and the intercept (-1.09 ± 0.32) were all significant (P < 0.001). The FFM model explained 69.3 % of the variance in O2,max, and the parameters (± s.e.e) lnFFM (0.772 ± 0.090), age (-0.0159 ± 0.0012) and the intercept (-1.57 ± 0.36) were significant (P < 0.001), while sex (0.077 +/- 0.038) was significant at P = 0.0497. Regardless of the model used, the age-associated decline was similar, with a relative decline of 15 % per decade (0.984 exp(age)) in O2,max in older humans being estimated. The study has demonstrated that, for a randomly drawn sample, the age-related loss in O2,max is determined, in part, by the loss of fat-free body mass. When this factor is accounted for, the loss of O2,max across age is similar in older men and women.

The present investigation was designed to examine whether calmodulin is involved in the inhibition of the ATP-sensitive K+ (KATP) channel by glucagon-like peptide 1(7-36) amide (GLP-1) in mouse pancreatic β-cells. Membrane potential, single channel and whole-cell currents through the KATP channels, and intracellular free Ca2+ concentration ([Ca2+]i) were measured in single mouse pancreatic β-cells. Whole-cell patch-clamp experiments with amphotericin-perforated patches revealed that membrane conductance at around the resting potential is predominantly supplied by the KATP channels in mouse pancreatic β-cells. The addition of 20 nM GLP-1 in the presence of 5 mM glucose significantly reduced the membrane KATP conductance, accompanied by membrane depolarization and the generation of electrical activity. A calmodulin inhibitor N-(6-aminohexyl)-5-chloro-1-naphthalenesulphonamide (W-7, 20 µM) completely reversed the inhibitory actions of GLP-1 on the membrane KATP conductance and resultant membrane depolarization. Cell-attached patch recordings confirmed the inhibition of the KATP channel activity by 20 nM GLP-1 and its restoration by 20 µM W-7 or 10 µM calmidazolium at the single channel level. Bath application of 20 µM W-7 also consistently abolished the GLP-1-evoked increase in [Ca2+]i in the presence of 5 mM glucose. These results strongly suggest that the mechanisms by which GLP-1 inhibits the KATP channel activity accompanied by the initiation of electrical activity in mouse pancreatic β-cells include a calmodulin-dependent mechanism in addition to the well-documented activation of the cyclic AMP-protein kinase A system. Experimental Physiology (2001) 86.3, 331-339.

In the presence of the muscarinic blocker atropine, the α-adrenoceptor blocker phentolamine and the β-adrenoceptor blocker propranolol (2 mg kg-1 of each, I.P.), the numerical density of parotid acinar secretory granules was reduced by 32 % in response to ascorbic acid (0.5 M) applied on the tongue every 30 s over 30 min in awake rats. This non-adrenergic, non-cholinergic (NANC) response was entirely dependent on an intact auriculo-temporal nerve supply. The NANC mechanisms were found to be potentially responsible for almost all of the exocytotic response that occurs in the absence of the three autonomic receptor blockers. No sympathetic contribution to the exocytotic response was found and furthermore, studies in parasympathetically denervated glands showed that the sympathetic contribution to the salivary flow was small. Experimental Physiology (2001) 86.4, 475-480.

The autonomic control of submandibular secretion has been investigated in fully weaned, anaesthetized calves 7 weeks after birth. Stimulation of the parasympathetic (chorda-lingual) innervation invariably produced a flow of saliva, the rate of which was frequency dependent over the range 2-8 Hz continuously. Neither the rate of flow nor the output of protein was enhanced by stimulating in bursts at relatively high frequencies. Stimulation of the sympathetic innervation (20 Hz for 1 s at 10 s intervals) alone produced a much slower flow of saliva but with a considerably higher protein content. Stimulation of both together produced no greater flow of saliva than occurred with either alone at the lower frequencies (2 and 4 Hz) but there was a pronounced synergy in respect of the secretion of protein. Following pre-treatment with propranolol (1·0 mg kg-1 I.V.), during on-going chorda-lingual stimulation at 4 Hz, intra-arterial injections of 1 nmol of either vasoactive intestinal peptide (VIP) or pituitary adenylate cyclase activating peptide (PACAP) elicited an increase in the flow and protein output of about the same order of magnitude. Calcitonin gene-related peptide (CGRP) also produced these same effects with roughly half the efficacy of VIP and PACAP but substance P had no detectable effect. It is concluded that VIP, PACAP and possibly CGRP are candidates for neurotransmitters with a role in the control of secretion in this gland.

The aim of this study was to evaluate whether long-term administration of L-arginine, a physiological substrate for the production of nitric oxide, improved blood pressure, heart rate, cardiac hypertrophy and particularly structural changes in the coronary and carotid artery of spontaneously hypertensive rats (SHR). The experiments started with three groups of 10-week-old animals: control Wistar rats, untreated SHR and SHR treated with L-arginine (SHR + L-arginine). L-Arginine was administered to SHR in a daily dose of 300 mg kg-1 intraperitoneally for 6 weeks. Blood pressure and heart rate were recorded each week. At the end of the experiment in one-half of each group heart weight and body weight were determined and the heart weight/body weight index was calculated. In the other animals, the cardiovascular system was perfused via the left ventricle with a glutaraldehyde fixative at 120 mmHg and the coronary and carotid arteries were processed for transmission electron microscopy. The inner diameter and wall thickness (tunica intima and tunica media) were measured on semithin sections. The reliability of the genetic feature in the SHR group was proved by the increased heart weight, heart weight/body weight index, wall thickness and wall thickness/inner diameter ratio of coronary and carotid arteries in comparison to the group of control Wistar rats. Long-term administration of L-arginine did not significantly influence blood pressure and heart rate in comparison with untreated SHR. Neither were any differences found in cardiac hypertrophy or the geometry of the coronary and carotid arteries (thickness of arterial wall, inner diameter, wall/diameter ratio). In conclusion, the changes in the cardiovascular system in SHR were not reversed, or even alleviated, by chronic treatment with L-arginine.

This study was performed to compare glucose metabolism in anaesthetised spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY) in an attempt to clarify whether this animal model of hypertension approximates the insulin-resistant state seen in human hypertension. With this aim the minimal model of glucose kinetics was applied to glucose and insulin data derived from a 12-sample, 120 min intravenous glucose tolerance test (IVGTT) performed in ten SHR and nine WKY rats under pentobarbital anaesthesia. This method provided two metabolic indices: the glucose effectiveness, SG, which quantifies the ability of glucose per se to enhance its rate of disappearance and to inhibit hepatic glucose production, and the insulin sensitivity, SI, which measures the ability of insulin to enhance plasma glucose disappearance and to inhibit hepatic glucose production. Systolic and diastolic arterial pressures in the SHR group were significantly higher (P < 0.0005) than in the WKY group. Mean SG and SI estimates from the SHR group (SG = 16.2 (± 2.0) × 10-2 dl min-1 kg-1 and SI = 12.5 (± 1.9) × 10-4 dl min-1 kg-1 (µU ml-1)-1) were not significantly different (P > 0.05) from mean estimates that characterised the WKY group (SG = 13.1 (± 1.5) × 10-2 dl min-1 kg-1 and SI = 15.8 (± 4.3) × 10-4 dl min-1 kg-1 (µU ml-1)-1). This result is in contrast with reported findings from humans in which insulin sensitivity is significantly reduced in the presence of hypertension.

Daily creatine supplements (0.258 g kg-1 ) were administered to adult male Wistar rats (n = 7) in the drinking water. Age matched rats (n = 6) acted as controls. After 5-6 days, contractile properties were examined in soleus and extensor digitorum longus (EDL) muscle strips in vitro at 30 °C. In soleus muscles, creatine supplements decreased the half-relaxation time of the isometric twitch from 53.6 ± 4.3 ms in control muscles to 48.4 ± 5.5 ms but had no effect on twitch or tetanic tension or on twitch contraction time. In EDL muscles twitch tension, tetanic tension, twitch contraction and half-relaxation times were all unaffected by creatine supplements. Creatine supplements increased the fatigue resistance of the soleus muscles but had no effect on that of the EDL muscles. After a 5 min low-frequency fatigue test, tension (expressed as a percentage of initial tension) was 56 ± 3 % in control soleus muscles, whereas that in the creatine-supplemented muscles was 78 ± 6 % (P < 0.01). In the EDL muscles, the corresponding values were 40 ± 2 % and 41 ± 9 %, respectively. The force potentiation which occurred in the EDL muscles during the initial 20-30 s of the fatigue test was 170 ± 10 % of initial tension in the control muscles 24 s after the initial stimulus train but was reduced (P < 0.01) to 130 ± 20 % in the creatine-supplemented muscles. In conclusion, soleus muscle endurance was increased by creatine supplements. EDL endurance was unaffected but force potentiation during repetitive stimulation was decreased. Experimental Physiology (2001) 86.2, 185-190.

We investigated the influence of ageing on the fatiguing characteristics of the mouse extensor digitorum longus (EDL) muscle as compared to those of the soleus muscle. Fatigue was produced by an intermittent stimulation protocol. We report for mature and aged animals the effects of fatigue on force produced during stimulation patterns that in non-fatigued muscle gave maximum force (Tmax, high frequency stimulation) and approximately half-maximum force (1/2Tmax, low frequency stimulation). In 15-month-old (mature) mice, fatiguing stimulation decreased Tmax in EDL and soleus muscle to 10.3 ± 1.0 % and 33.4 ± 3.0 % of control, respectively. In 30-month-old (aged) mice, the decrease in Tmax in EDL and soleus was statistically equal to that of the younger animals. Fatiguing stimulation decreased 1/2Tmax in EDL and soleus from 15-month-old animals to 22.5 ± 2.9 % and 45.7 ± 0.3 % of control, respectively. In 30-month-old animals, the 1/2Tmax in EDL and soleus muscle decreased to 18.2 ± 1.3 % and 35.0 ± 3.6 % of control, respectively. Under all conditions, the soleus fatigued significantly less. Contractile recovery from fatiguing stimulation was complete for the soleus in both age groups after 30 min, but incomplete for the EDL. The 1/2Tmax/Tmax ratio significantly increased in EDL and soleus muscle from 15-month-old animals after fatiguing stimulation. This increase was less significant in EDL, and absent in soleus muscle, from 30-month-old animals. These results indicate that fatiguing stimulation induces a leftward shift in the force-frequency relationship in the young animals; this shift is either significantly less (EDL) or absent (soleus) in the older animals. We speculate that the leftward shift of the force-frequency relationship may reflect a protective mechanism in younger animals against some of the damaging effects of fatiguing stimulation (i.e. oxidative stress). Experimental Physiology (2002) 87.1, 77-82.

This study was designed to find out if the lymph flow, indicated as albumin clearance, from active skeletal muscle is maintained constant during a prolonged steady-state exercise. 99mTc-labelled albumin was injected bilaterally into the vastus lateralis muscles of eight endurance-trained men. The radioactivity at the injection site was monitored by a gamma-camera before, frequently during, and after a 2 h run at a controlled steady intensity of 69 ± 4 % of the maximal heart rate. The fractional clearance rate of albumin was calculated for each monitoring interval, and was expressed as percentage clearance per minute (% min-1). During the first 15 min of exercise the clearance rate was five times higher than at rest before the exercise (0.29 ± 0.12 vs. 0.06 ± 0.05 % min-1, P = 0.001). During the next 25 min of running the clearance rate fell to 0.19 ± 0.08 % min-1 (P = 0.02), from which level it was further attenuated, being 0.12 ± 0.04 % min-1 at the end of the exercise. After the exercise the clearance rate fell rapidly to the level of 0.04 ± 0.03 % min-1. The results showed that the albumin clearance from working muscles is not constant during steady-state exercise, suggesting that lymph flow from exercising skeletal muscle may not be constant despite lymphatic pumping being assumed to be unchanged during the course of exercise (i.e. constant exercise intensity and running speed).

Lateral ventricular volumes were monitored and quantified using accurately registered magnetic resonance images (MRIs) in six healthy individuals 30 min before and up to 4 h after ingestion of a glucose drink. The volume of the lateral ventricles increased by an average (± S.E.M.) of 2Σ4 ± 0Σ4 % as blood glucose levels rose from 4Σ8 ± 0Σ2 mmol l-1 to 8Σ4 ± 0Σ4 mmol l-1. This was followed by a peak decrease of 5Σ99 ± 3Σ3 % below initial fasting volumes as blood glucose levels fell to 5Σ0 ± 0Σ3 mmol l-1. We suggest that the secondary volume decrease demonstrates a homeostatic process of brain volume regulation for which the mechanism remains uncertain.

This study investigated if prior eccentric contractions, and thus mechanical strain and muscle damage, exert an effect on the muscle membrane phospholipid fatty acid composition in rats, and whether a possible effect could be attenuated by dietary supplements. Twenty-three rats were randomised to three groups who received chow with added fish oil (n = 8), vitamin C (n = 8) or no supplement (n = 7). After 3 weeks of feeding, calf muscles on one side were stimulated electrically during anaesthesia causing eccentric contractions. Two days later the white gastrocnemius, a part of the stimulated calf muscle, was excised from both legs. In the muscles stimulated to contract eccentrically, compared to the control muscles, the proportion of arachidonic acid, C20:4,n-6 (17.7 ± 0.6; 16.4 ± 0.4 % of total fatty acids, respectively) and docosapentanoeic acid, C22:5,n-3 (2.9 ± 0.1 and 2.7 ± 0.1 % of total fatty acids, respectively) was uniformly higher across groups (P < 0.02) with no differences between diet groups. The proportion of long chain polyunsaturates was also significantly higher in the eccentrically contracted (39.9 ± 0.6 % of total fatty acids) compared to the control leg (38.2 ± 0.6 % of total fatty acids; P < 0.01). In contrast no differences were observed in the fatty acid composition of the triacylglycerols stored within the muscle. Thus one severe bout of eccentric contractions modulates the fatty acid composition of the muscle membrane phospholipids when compared to a control leg, and supplemental intake of fish oil or vitamin C did not attenuate this effect. Experimental Physiology (2001) 86.5, 599-604.

The cellular uptake of glucose catalysed by the facilitated glucose transporter (GLUT) family is further regulated by metabolites and hormones, most importantly by insulin. All of the six isoforms known in this family possess a large cytoplasmic domain of divergent amino acid sequence. A body of evidence indicates that this domain is important for GLUT regulation. Exactly how this domain participates in the regulation, however, is not known. A likely possibility is that a specific cellular protein interacts with GLUT at this domain, and thus modulates the function. This putative, glucose transporter binding protein (GTBP) may be an enzyme, or a non-enzymic adaptor or docking protein. Indeed, we have identified several cellular proteins that bind to the cytoplasmic domain of GLUT proteins; these include glyceraldehyde-3-phosphate dehydrogenase, glucokinase, GTBP70, GTBP85, GTBP28 and L-3-hydroxyacyl-CoA dehydrogenase. Some of these GLUT-GTPB interactions are functionally coupled. Whether any of these interactions actually participates in the insulin-induced GLUT regulation is yet to be determined.

Alleviation of muscle ischaemia by improving capillary supply has proved difficult, possibly reflecting the inability to substantially increase blood flow. We reasoned that muscle overload, which induces angiogenesis in the absence of altered blood flow, may be an alternative to drug therapy. Male Wistar rats underwent unilateral ligation of the common iliac artery, with or without ipsilateral extirpation of the tibialis anterior muscle. Six weeks later ischaemic (I) extensor digitorum longus (EDL) had a 10% (P< 0.05) decrease in relative muscle mass, while overloaded muscles (O) had undergone hypertrophy of 39% and 52% relative to contralateral (CL) and control (C) muscle masses, respectively (P<0.01). Muscle atrophy was prevented by the combination of overload and ischaemia (O/I), with hypertrophy of 24% (vs. CL) and 35% (vs. C), respectively (P<0.01). Changes in muscle fibre cross-sectional area paralleled the changes in muscle mass, with means of 1898 ± 59, 1531 ± 90, 2253 ± 155 and 2292 ± 80 mm2 for C, I, O and O/I, respectively (P<0.01 vs. C and I). Capillary to fibre ratio (C:F) was significantly increased in overloaded (2.58 ± 0.09) compared to contralateral (1.78 ± 0.04), control (1.61 ± 0.05) and ischaemic (1.73 ± 0.06) muscles (P<0.001). A similar increase in C:F was seen in overloaded plus ischaemic muscle (2.59 ± 0.07) compared to contralateral (1.40 ± 0.01) and control or ischaemic values (P<0.01). In both O and O/I muscle groups, C:F and capillary density (CD) increased most in the region of EDL where fibre size was largest, while hypertrophy of fibres was least in the same region for both groups. These data suggest that the microvascular deficit evident in chronic muscle ischaemia may be alleviated by angiogenesis that is induced by mechanical stimuli via chronic muscle overloaded.

Interstitial adenosine concentrations in red soleus (SL) or white extensor digitorum longus (EDL) muscles of anaesthetised rats were determined using microdialysis and HPLC. Systemic hypoxia was induced by ventilating the animals with 10 % oxygen in nitrogen for 15 min: arterial PO2 decreased from 111.8 ± 10.9 to 42.2 ± 4.3 mmHg (n = 4; P < 0.01) and mean systemic arterial blood pressure from 97.6 ± 4.9 to 59.0 ± 3.6 mmHg (n = 22; P < 0.001). The interstitial adenosine concentration was not significantly changed from its control values of 294 ± 44 nM (n = 20) in EDL and 302 ± 36 nM (n = 20) in SL during hypoxia or the recovery period. The interstitial lactate concentration did not change in the early part of the hypoxia but increased from 1.0 ± 0.2 to 1.4 ± 0.3 mM (n = 6; P < 0.05) in SL and from 2.0 ± 0.4 to 2.4 ± 0.4 mM (n = 6; P < 0.05) in EDL during the later part of the hypoxia, and remained elevated in the recovery period. Muscle contractions (2 Hz for 15 min) produced a transient increase in the interstitial adenosine concentration of SL from 150 ± 35 to 244 ± 75 nM (n = 10; P < 0.05) during the first 5 min of stimulation. In EDL the interstitial adenosine concentration increased from 145 ± 50 to 435 ± 144 nM (n = 10; P < 0.05) in the later part of the contraction and remained elevated in the early part of the recovery period. These data suggest that: (i) in systemic hypoxia adenosine does not appear in the interstitial space, which rules out its release from skeletal muscle, although it may be formed by the vascular tissues in this condition; (ii) adenosine is formed in the interstitial space of skeletal muscle during muscle contractions; (iii) there is slow clearance of adenosine from the interstitial space of white muscle, perhaps due to the low vascularity of the tissue. Experimental Physiology (2001) 86.5, 593-598.

In chickens, we have shown that intestinal absorption of glucose via apical SGLT1 and basolateral GLUT2 transport systems is affected by dietary Na+; low-Na+ adapted birds show a dramatic reduction of glucose transporters in both membranes in the rectum, an intermediate response in the ileum and no effects in the jejunum. We have now studied the effect of resalination of low-Na+ adapted chickens on glucose kinetics across SGLT1 (using α -methyl-D-glucoside as substrate) and GLUT2 (using D-glucose) and on the specific binding of phlorizin and cytochalasin B, respectively. Twelve-week-old male Leghorn chickens were fed wheat and barley with drinking water containing either 150 mM NaCl (high-Na+ group) or 0.015 mM (low-Na+ group) for 14 days (serum aldosterone: 242 ± 6 pg ml-1 in the low-Na+ and 46 ± 4 pg ml-1 in the high-Na+ group). On day 14, the low-Na+ group was either resalinated with an oral dose of NaCl (9 g (kg body wt)-1) or switched to the high-Na+ condition, for 1 week. Serum aldosterone measured 4 h, 1 day and 7 days after the change in NaCl intake fell to between 30 and 39 pg ml-1. The changes in apical α-methyl-D-glucoside and basolateral D-glucose transport observed in the ileum and rectum of low-Na+ adapted animals were completely reversed by resalination within 4 h of NaCl administration to the level of values observed for high-Na+ adapted birds. The good correlation between the α-methyl-D-glucoside and D-glucose Vmax and the SGLT1 and GLUT2 density, respectively, supports the view that the increase in apical and basolateral hexose transport found in the ileum and rectum of both groups of resalinated birds is due to an increase in the number of protein transporters. The rapid changes in the number of glucose transporters observed suggest that the target of the regulatory signal(s) involved are the mature enterocytes present in the villi rather than the developing enterocytes in the crypt.

We have previously shown that feeding 50 ml of colostrum can increase the thermogenic activity of brown adipose tissue (BAT) in newborn lambs maintained at a warm (30¡C) ambient temperature. This study further examines the effect of ambient temperature on BAT and thermoregulation by investigating the response to feeding 50 ml of water. Immediately after vaginal birth, lambs were placed in either a warm (30¡C) or cool (15¡C) environment at ambient temperature and measurements of colonic temperature and heat production were recorded for 6 h. Lambs were fed 50 ml of water when 5 h old. The level of guanosine 5'-diphosphate (GDP) binding was higher, but adrenaline content lower in BAT sampled from lambs maintained at 15¡C compared with those at 30¡C. Feeding was associated with an increase in colonic temperature and plasma concentrations of glucose and non-esterified fatty acids in lambs maintained at 15¡C only. In this group plasma concentrations of adrenaline and dopamine declined after feeding, but noradrenaline concentrations were not influenced by feeding in either group of lambs. O2 consumption and CO2 production were higher in lambs maintained at 15¡C but were not influenced by ambient temperature or feeding. It is concluded that feeding a small volume of water can influence thermoregulation by a mechanism that is dependent on the ambient temperature at which the lamb is maintained.

During prolonged exercise in a cold environment, fatigue is generally associated with a depletion of endogenous glycogen stores. This has lead many authors to hypothesize that the carbohydrate (CHO) content of fluids ingested in cool environments should be high, yet this hypothesis has not been specifically examined. In the present study, six healthy males cycled to exhaustion at approximately 80 % of their maximum oxygen consumption ([Vdot]O2,max) with either no drink (ND), a 15 % CHO-electrolyte drink (15 % CHO) or a 2 % CHO-electrolyte drink (2 % CHO). Dietary intake and exercise were replicated 2 days prior to each trial. Mean (S.D.) ambient temperature was 10·0 (0·3)°C with a relative humidity of 72 (2) % and an air velocity of approximately 0·7 m s-1 on all trials. Weighted mean skin temperature was calculated, and rectal temperature and heart rate were recorded at rest, during exercise and at exhaustion. Venous samples were drawn before and during exercise and at exhaustion for determination of haemoglobin, haematocrit, blood metabolites and serum electrolytes and osmolality. Expired air was collected for calculation of [Vdot]O2 and respiratory exchange ratio which were used to estimate rates of fuel oxidation. Ratings of perceived exertion (RPE) were also obtained. Exercise capacity was not different (P = 0·49) between trials, with median (range) times to exhaustion of 90·6 (66·8-106·0), 97·7 (60·9-112·0) and 102·0 (77·1-170·7) min for the ND, 15 % CHO and 2 % CHO trials, respectively. The 15 % CHO drink significantly (P < 0·05) elevated blood glucose concentration and total CHO oxidation compared with the ND trial. The 2 % CHO drink significantly (P < 0·05) reduced the estimated change in plasma volume and resulted in a lower serum osmolality than the other two trials. No differences were observed in any thermoregulatory or cardiorespiratory responses between trials. These data suggest that maintenance of blood-borne substrate and/or plasma volume does not influence exercise capacity in the cold, as is commonly reported during this type and intensity of exercise in warmer environments.