Presence of HHV-6 genome in spermatozoa in a context of couples with low fertility: what type of infection?

Human herpesvirus-6 (HHV-6) is a betaherpesvirus whose genome may integrate into human chromosomes. Chromosomally integrated HHV-6 (ciHHV-6) may be transmitted vertically from parents to children. HHV-6 DNA has been detected in semen, but its integrated or extrachromosomal status has not yet been characterised. The aim of this study was to determine the prevalence of HHV-6 DNA and to search for ciHHV-6 forms in spermatozoa purified from semen obtained from subjects explored for low fertility. A total of 184 sperm samples were purified using PureSperm(®) . HHV-6 viral load and species identification were performed by real-time polymerase chain reaction. Of 179 sperm specimens analysed, three were positive for HHV-6 (1.7%). Two samples (1.1%) had viral loads of 680 232 and 2 834 075 copies per million spermatozoa, compatible with loads expected for a ciHHV-6 form. The viral load of the third positive sample (73 684 copies per million spermatozoa) was lower than would be expected for ciHHV-6 infection, implying that the HHV-6 DNA detected in spermatozoa corresponds mainly to ciHHV-6. However, viral DNA may also be detected at a low level that is not in favour of the presence of ciHHV-6. Further studies are necessary to determine the origin of detected viral genomes.

Metabolic and hormonal responses to exercise in the anti-obese Lou/C rats.

OBJECTIVE: Lou/C rats are a substrain of Wistar rats that exhibit a spontaneous low caloric intake and no development of obesity with age. Recently, we reported that Lou/C rats, compared to equally food-restricted Wistar counterparts, show lower resting levels of plasma glucose, epinephrine and liver glycogen. To further explore this metabolic particularity, we used exercise (swimming 60 min) as a situation of high-energy demand, to test the ability of Lou/C rats to maintain euglycemia. DESIGN: Male Lou/C rats (14-week-old) were compared to age-matched male Wistar rats fed either ad libitum (WAL) or Wistar rats whose food was chronically restricted (WFR) to the same caloric intake as the Lou/C rats. RESULTS: In spite of low liver glycogen stores ( approximately 50% of normal values), Lou/C rats were able to maintain euglycemia during exercise even though liver glycogen breakdown was blunted. The decreased use of glycogen during exercise in Lou/C rats was associated with a reduced epinephrine response compared to WFR animals. By contrast, WFR were also able to maintain euglycemia during exercise but at the expense of a significant (P<0.01) decrease in liver and muscle glycogen content. Plasma free fatty acid and glycerol concentrations were increased (P<0.01) similarly in all three groups during exercise. In a separate experiment conducted in isolated hepatocytes from 24 h fasted Lou/C and Wistar rats, it was found that gluconeogenic flux from glycerol was found to be significantly (P<0.01) higher in Lou/C than in Wistar rats (5.4+/-0.2 vs 3.7+/-0.1 micromol/min/g dry cells). Resting and exercising plasma leptin levels were also significantly (P<0.05) lower in Lou/C than in the two other groups. CONCLUSION: It is concluded that Lou/C rats have the particularity to rely spontaneously less on their liver glycogen stores to meet their energy demands during exercise while maintaining euglycemia.

Effect of voluntary exercise on H2O2 release by subsarcolemmal and intermyofibrillar mitochondria.

Previous data have demonstrated that, to handle the oxidative stress encountered with training at high intensity, skeletal muscle relies on an increase in mitochondrial biogenesis, a reduced H(2)O(2) production, and an enhancement of antioxidant enzymes. In the present study, we evaluated the influence of voluntary running on mitochondrial O(2) consumption and H(2)O(2) production by intermyofibrillar mitochondria (IFM) and subsarcolemmal mitochondria (SSM) isolated from oxidative muscles in conjunction with the determination of antioxidant capacities. When mitochondria are incubated with succinate as substrate, both maximal (state 3) and resting (state 4) O(2) consumption were significantly lower in SSM than in IFM populations. Mitochondrial H(2)O(2) release per unit of O(2) consumed was 2-fold higher in SSM than in IFM. Inhibition of H(2)O(2) formation by rotenone suggests that complex I of the electron transport chain is likely the major physiological H(2)O(2)-generating system. In Lou/C rats (an inbred strain of rats of Wistar origin), neither O(2) consumption nor H(2)O(2) release by IFM and SSM were affected by long-term, voluntary wheel training. In contrast, glutathione peroxidase and catalase activity were significantly increased despite no change in oxidative capacities with long-term, voluntary exercise. Furthermore, chronic exercise enhanced heat shock protein 72 accumulation within skeletal muscle. It is concluded that the antioxidant status of muscle can be significantly improved by prolonged wheel exercise without necessitating an increase in mitochondrial oxidative capacities.

Lactate and epinephrine during exercise in altitude natives.

We tested the hypothesis that the reported low blood lactate accumulation ([La]) during exercise in altitude-native humans is refractory to hypoxianormoxia transitions by investigating whether acute changes in inspired O2 fraction (FIo2) affect the [La] vs. power output (W) relationship or, alternatively, as reported for lowlanders, whether changes in [La] vs. W on changes in FIo2 are related to changes in blood epinephrine concentration ([Epi]). Altitude natives [n = 8, age 24 +/- 1 (SE) yr, body mass 62 +/- 3 kg, height 167 +/- 2 cm] in La Paz, Bolivia (3,600 m) performed incremental exercise with two legs and one leg in chronic hypoxia and acute normoxia (AN). Submaximal one- and two-leg O2 uptake (Vo2) vs. W relationships were not altered by FIo2. AN increased two-leg peak Vo2 by 10% and peak W by 7%. AN paradoxically decreased one-leg peak Vo2 by 7%, whereas peak W remained the same. The [La] vs. W relationships were similar to those reported in unacclimatized lowlanders. There was a shift to the right on AN, and maximum [La] was reduced by 7 and 8% for one- and two-leg exercises, respectively. [Epi] and [La] were tightly related (mean r = 0.81) independently of FIo2. Thus normoxia attenuated the increment in both [La] and [Epi] as a function of W, whereas the correlation between [La] and [Epi] was unaffected. These data suggest loose linkage of glycolysis to oxidative phosphorylation under influence from [Epi]. In conclusion, high-altitude natives appear to be not fundamentally different from lowlanders with regard to the effect of acute changes in FIo2 on [La] during exercise.

Coca chewing for exercise: hormonal and metabolic responses of nonhabitual chewers.

To determine the effects of acute coca use on the hormonal and metabolic responses to exercise, 12 healthy nonhabitual coca users were submitted twice to steady-state exercise (approximately 75% maximal O2 uptake). On one occasion, they were asked to chew 15 g of coca leaves 1 h before exercise, whereas on the other occasion, exercise was performed after 1 h of chewing a sugar-free chewing gum. Plasma epinephrine, norepinephrine, insulin, glucagon, and metabolites (glucose, lactate, glycerol, and free fatty acids) were determined at rest before and after coca chewing and during the 5th, 15th, 30th, and 60th min of exercise. Simultaneously to these determinations, cardiorespiratory variables (heart rate, mean arterial blood pressure, oxygen uptake, and respiratory gas exchange ratio) were also measured. At rest, coca chewing had no effect on plasma hormonal and metabolic levels except for a significantly reduced insulin concentration. During exercise, the oxygen uptake, heart rate, and respiratory gas exchange ratio were significantly increased in the coca-chewing trial compared with the control (gum-chewing) test. The exercise-induced drop in plasma glucose and insulin was prevented by prior coca chewing. These results contrast with previous data obtained in chronic coca users who display during prolonged submaximal exercise an exaggerated plasma sympathetic response, an enhanced availability and utilization of fat (R. Favier, E. Caceres, H. Koubi, B. Sempore, M. Sauvain, and H. Spielvogel. J. Appl. Physiol. 80: 650-655, 1996). We conclude that, whereas coca chewing might affect glucose homeostasis during exercise, none of the physiological data provided by this study would suggest that acute coca chewing in nonhabitual users could enhance tolerance to exercise.

Central and peripheral noradrenergic responses to 14 days of spaceflight (SLS-2) or hindlimb suspension in rats.

INTRODUCTION: The purposes of this work were to assess the influence of microgravity on the central and peripheral noradrenergic activity to reevaluate SLS-1 mission findings and to compare it with that of simulated microgravity in rats. METHODS: The norepinephrine (NE) contents of the brainstem cell groups (A1, A2, A5, and A6) and organs (heart and kidneys) involved in blood pressure regulation were determined in rats after a 14-d spaceflight (SLS-2 with animals sacrificed 6 h after landing) and after a 14-d hindlimb suspension followed with 6 h of recovery. RESULTS: After SLS-2 spaceflight, NE contents were not significantly different between flight and ground-based rats either in A1 (5.2 +/- 0.5 vs. 5.7 +/- 0.4 pmol/structure), rostral A2 (12.1 +/- 0.5 vs. 11.1 +/- 0.9 pmol/structure), caudal A2 (3.2 +/- 0.6 vs. 4.3 +/- 0.5 pmol/structure) and A5 (4.4 +/- 0.4 vs. 4.3 +/- 0.5 pmol/structure) nuclei or in cardiac atria (98.6 +/- 7.5 vs. 83.4 +/- 8.9 pmol.mg-1 protein), ventricles (38.3 +/- 2.2 vs. 44.1 +/- 2.8 pmol.mg-1 protein) and kidneys (13.4 +/- 0.8 vs. 17.7 +/- 1.5 pmol.mg-1 protein). NE content was unchanged in A6 nucleus after SLS-2 comparing with control rats (respectively 4.1 +/- 0.3 vs. 4.5 +/- 0.5 pmol/structure), while it was depleted after SLS-1 mission (2.9 +/- 0.3 vs. 8.8 +/- 0.7 pmol/structure, p < 0.001) probably in relation with the stressful conditions on return to Earth. Similarly, no alterations between suspended and control rats were noted in central and peripheral NE contents after 14 d of suspension and after 6 h of recovery, whereas NE turnover studies evidenced large changes in the activities on structures on suspension and on recovery. CONCLUSION: These results suggest that only NE turnover determination will provide information about the role of the sympathetic system in the cardiovascular deconditioning. This raises the problem of the necessity to experiment inflight (injections, sacrifice) in order to avoid the recovery effects of the few hours following the landing.

Hormonal and metabolic adjustments during exercise in hypoxia or normoxia in highland natives.

In sea-level natives, exposure to hypoxia for a few weeks is characterized by an increased dependence on blood glucose and a decreased reliance on lactate for energy metabolism during exercise. These metabolic adjustments have been attributed to behavioral changes in the sympathoadrenergic and pancreatic systems. The aim of this study was to test the hypothesis of a reduced sympathoadrenergic activation and subsequent metabolic changes when high-altitude natives are acutely exposed to normoxia. Young Andean natives performed incremental exercise to exhaustion during hypoxia (arterial PO2 55.1 +/- 1.1 Torr) or during acute normoxia (arterial PO2 78.7 +/- 1.7 Torr). As a whole, oxygen uptake was increased in normoxia compared with hypoxia during graded exercise. This finding is not related to a decrease in anaerobic metabolism but rather is interpreted as a consequence of a shift in substrate utilization during exercise (increased contribution of fat as assessed by a reduction in the respiratory exchange ratio). These metabolic changes are not accompanied by modifications of glucoregulatory hormones (catecholamines, insulin, and glucagon). In particular, the exercise-induced catecholamine secretion was similar in chronic hypoxia and acute normoxia. As a consequence, blood lactate accumulation during incremental exercise was similar in both conditions. It is concluded that high-altitude natives do not display any sign of a greater sympathoadrenergic activation during chronic hypoxia and that the exercise-induced hormonal changes remained unaffected by acute inhalation of a normoxic gas mixture.

Effects of coca chewing on metabolic and hormonal changes during graded incremental exercise to maximum.

We examined the effects of 1 h of coca chewing on metabolic and hormonal responses during incremental exercise to exhaustion in traditional coca chewers (C; n = 8), and the results were compared with a group of nonchewers (n = 13). For 1 h, C chewed approximately 12 g of coca leaves that resulted in the apparition of cocaine in blood that reached 72 +/- 9 ng/ml. In resting conditions, even though sympathoadrenergic activity (as assessed by norepinephrine and epinephrine plasma levels) was similar in both groups, C displayed a higher level of plasma free fatty acids. Oxygen uptake measured at exhaustion and delta work efficiency during exercise were similar in both groups. During the incremental exercise, C displayed a significantly lower arterial oxygen saturation that cannot be explained by a reduced ventilatory response after coca chewing. In fact, even at maximal exercise, both ventilatory output and ventilatory equivalent were higher in C compared with nonchewers. It is concluded that the beneficial effects of coca chewing on exercise tolerance reported frequently by traditional coca users is not related to either an improved maximal exercise capacity or an increased work efficiency. However, during incremental exercise, coca chewing appeared to result in an increased free fatty acid availability that could be beneficial for prolonged submaximal exercise.

Effects of coca chewing on hormonal and metabolic responses during prolonged submaximal exercise.

The effects of coca chewing on prolonged submaximal exercise responses were investigated in chronic coca chewers and compared with a group of nonchewers. At rest, coca chewing during a 1-h period was followed by a significant increase in blood glucose, free fatty acid, and norepinephrine concentrations and a significant reduction in insulin plasma level. During prolonged (1-h) submaximal (65-70% peak O2 uptake) exercise, chewers displayed a significantly greater adrenergic activation (as evidenced by a higher level of plasma epinephrine) and an increased use of fat (as evidenced by a lower respiratory exchange ratio). The gradual increase in oxygen uptake (O2 drift) commonly observed during prolonged exercise was blunted in coca chewers. This blunting in O2 drift is not related to coca-induced changes in ventilatory or lactate responses to exercise but could possible be related to an enhanced glucose utilization by chewers during the late phase of exercise. The present results provide experimental evidence of the physiological effects of coca chewing that could explain the better ability of coca users to sustain strenuous work for an extended period of time.

Lactate and catecholamine responses in male and female sprinters during a Wingate test.

A total of six male and six female sprinters at the same national competition level and aged 18-20 years performed a force/velocity test and a 30-s supramaximal exercise test (Wingate test) on 2 different days, separated by a maximal interval of 15 days. The maximal anaerobic power (Wmax) was determined from the force/velocity test, and the mean anaerobic power (W) from the Wingate test. Immediately after the Wingate test, a 5-ml venous blood sample was drawn via a heparinized catheter in an antebrachial vein for subsequent catecholamine (adrenaline and noradrenaline) analysis. After 5 min recovery a few microliters of capillary blood were also taken for an immediate lactate determination. Even expressed per kilogram lean body mass, Wmax and W were significantly lower in women. The lactate and adrenaline responses induced by the Wingate test were also less pronounced in this group whereas the noradrenaline levels were not significantly different in men and women. Above all, very different relationships appeared between lactate, adrenaline, noradrenaline and W according to sex. Thus, as reported by other authors, the adrenergic response to a supramaximal exercise seemed to be lower in women than in men. Nevertheless a different training status between the two groups, even at same national competition level, could not be excluded and might contribute, at least in part, to the gender differences observed in the present study.

Glucoregulation and hormonal changes during prolonged exercise in boys and girls.

A group of 17 children, 8.5-11 years old, performed a 60-min cycle exercise at 60% of maximal oxygen uptake (VO2max) 2 h after a standardized breakfast. They were 10 young boys (pubertal stage = 1) and 7 young girls (pubertal stage < or = 2) of similar VO2max (respective values were 48.5 ml min-1 kg-1, SEM 1.8; 42.1 ml min-1 kg-1, SEM 2.4). Blood samples of 5 ml were withdrawn by heparinized catheter, the subjects being in a supine position, 30 min before the test, then after 0, 15, 30 and 60 min of exercise and following 30 min recovery. Haematocrit was immediately measured. Thereafter plasma was analysed for glucose, non-esterified fatty acid, glycerol, catecholamine (noradrenaline, adrenaline), insulin and glucagon concentrations. This study showed two main results. First, the onset of exercise induced a significant glucose decrease (of about 11.4%) in all the children. Secondly, both the glycaemic and the hormonal responses were obviously different according to the sex. In boys only, the initial glucose drop was significantly correlated to the pre-exercise insulin values. Whatever the time, the glycaemic levels and the catecholamine responses were lower in girls than in boys, whereas the insulin values remained higher. However, none of these two hormonal parameters seemed to be really responsible for the lower glucose values in girls. On the one hand, the great individual variability of noradrenaline and adrenaline and differences in their relative intensity at the end of the exercise between boys and girls might contribute to the lower catecholamine levels in girls.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of adrenalectomy or RU-486 on rat muscle fibers during hindlimb suspension.

The purpose of this study was to investigate the effects of a glucocorticoid antagonist, RU-486, and of adrenalectomy (ADX) on rat skeletal muscle structural properties after 3, 7, and 14 days of hindlimb suspension (H). After H, a significant loss in muscle weight was observed as early as 3 days in soleus (SOL; -10%) and adductor longus (AL; -14%) muscles. In SOL, after only 7 days, a reduction (-14%) in type I fiber percent distribution occurred, accompanied by an increase (+129%) in intermediate type I fibers. Fiber type changes increased depending on the duration of H. In AL muscle, no change occurred after H in the fiber type composition despite a similar degree of muscle atrophy. Treatment with RU-486 or ADX significantly reduced the loss of SOL weight observed after 14 days (-42 and -44%, respectively, vs. -50% for H rats), delayed the SOL atrophy (from 3 to 7 days), and normalized the shift in fiber type distribution induced by H. In SOL, administration of RU-486 (but not ADX) partly prevented the reduction in size induced by H of all the fibers. In AL, neither treatment affected the extent of muscle atrophy, even though the reduction in type IIa fiber size was prevented by RU-486 but not by ADX after 14 days of suspension. ADX or RU-486 administration did not prevent the extensor digitorum longus weight loss observed after 14 days of suspension but allowed a recovery of its normal fiber type composition.(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise training fails to prevent glucocorticoid-induced muscle alterations in young growing rats.

The aim of this study was to determine the impact of chronic treatment for 8 weeks with hydrocortisone acetate (5 mg kg-1 day-1) on skeletal muscles, and to evaluate whether sprint training can prevent glucocorticoid-induced muscle atrophy better than endurance training. Biochemical, histological and contractile properties were employed to determine the influence of this steroid on skeletal musculature, and the results were compared to pair-weight animals to take into account the influence of corticoids on growth rate. It was found that hydrocortisone acetate treatment results in a stunted growth, adrenal atrophy and depressed plasma corticosterone levels. Mild corticoid-induced losses of muscle mass and protein content (9%-13%) were observed in fast-twitch skeletal muscles. It appeared that the impact of corticoids is strictly directed toward type IIb fibres, which displayed a 12%-18% reduction in cross-sectional areas. No alterations occurred in plantaris contractile speed or tensions properties. Neither endurance training (30 m/min; 90 min/day; 5 days/week) nor sprint training (60 m/min; 15 min/day; 5 days/week) for 8 weeks was able to counteract the effects of corticoids. These data suggest that increased contractile activity, as induced by treadmill running, is not sufficient to counteract the muscular effects of glucocorticoids when administered at a dose of 5 mg kg-1 day-1.

Soleus muscle alterations in spontaneously hypertensive rats are not dependent on activation of beta 2-adrenergic receptors.

The effects of selective beta 2-adrenergic blockade with ICI 118,551 on the histochemical, biochemical, and contractile properties of slow-twitch soleus muscle from spontaneously hypertensive (SHR) and normotensive (WKY) rats were examined from birth to 8-10 weeks of age. Chronic treatment of normotensive rats with ICI 118,551 caused an impairment in the differentiation of slow type fibers during development but failed to alter the fiber type distribution of hypertensive rats. beta 2-Adrenoreceptor blockade was ineffective in reducing the enhanced glycolytic and oxidative capacities of soleus in hypertensive rats. The suggestion can be made that beta 2-adrenoreceptor activation is not responsible, at least directly, for the histochemical and biochemical alterations of slow muscle from hypertensive rats.

Decreased norepinephrine turnover rate in the brown adipose tissue of pre-obese fa/fa Zucker rats.

Norepinephrine (NE) content and turnover rate, and the activity of dopamine-beta-hydroxylase (DBH) were measured in the brown adipose tissue (BAT) of developing Zucker rats of the three genotypes: Fa/Fa and Fa/fa (with a lean phenotype) and fa/fa (phenotypically obese). As early as 15 days of age, namely at a pre-obese stage, BAT NE content and turnover rate are already reduced in fa/fa rats, just like they are at 50 days. The development of DBH activity is completely impaired in fa/fa rats. These results demonstrate that the reduction in sympathetic tone in BAT of fa/fa rats is already present before the onset of phenotypic obesity.

Glucose and free fatty acid utilization during prolonged exercise in prepubertal boys in relation to catecholamine responses.

Ten prepubertal boys performed 60-min cycle exercise at about 60% of their maximal oxygen uptake as previously measured. To measure packed cell volume, plasma glucose, free fatty acids (FFA), glycerol and catecholamines, blood samples were drawn at rest using a heparinized catheter and at the 15th, 30th and 60th min of the exercise and after 30 min of recovery. At rest, the blood glucose concentrations were at the lowest values for normal. Exercise induced a small decrease of blood glucose which was combined with an abrupt increase of the noradrenaline concentration during the first 15 min. The FFA and glycerol concentrations increased throughout the exercise linearly with that of adrenaline. Compared to adults, the FFA uptake expressed per minute and per litre of oxygen uptake was greater in children. These results suggested that it is difficult for children to maintain a constant blood glucose concentration and that prolonged exercise provided a real stimulus to hypoglycaemia. An immediate and large increase in noradrenaline concentration during exercise and a greater utilization of FFA was probably used by children to prevent hypoglycaemia.

Fasting-induced rise in locomotor activity in rats coincides with increased protein utilization.

The aim of this study was to investigate the possible relation between the modifications in locomotor activity (on running wheel) which occur during prolonged fasting and changes in the utilization of energy reserves. In 18-week-old rats, we found that the rate of body mass loss reflects the changes in nitrogen excretion that occur over three phases of fasting: (I) initially decreasing, (II) maintained at a low level and (III) increasing. Locomotor activity started to increase during phase II without a change in its nycthemeral pattern. By contrast, the 10-fold higher daily locomotor activity that occurred in phase III was marked by a higher proportion of diurnal activity. Using 9-, 18-, and 33-week-old rats, in order to obtain a different timing in the metabolic changes during fasting, we could confirm the coincidence between the later rise in locomotor activity and the occurrence of phase III. Refeeding of rats of either age in phase III rapidly suppressed fasting-induced changes in locomotor activity. These data accord with the idea that behavioral changes reflecting the search for food are triggered by a later and reversible change in the utilization of body protein vs. lipid stores during prolonged fasting.

Resistance of hepatic glycogen to depletion in obese Zucker rats.

Glycogen stores (liver and carcass) have been studied in lean and obese Zucker rats. The animals were submitted to one of three feeding conditions: ad libitum, a 48-h fast, or a 48-h fast and food ad libitum for 24 h, and to two environmental conditions, either thermoneutrality or an acute cold exposure (2 days at 4-7 degrees C). After a 2-day fast at 25 degrees C, the liver glycogen store was reduced by 45 times in the lean rats, while it was decreased by only 3 times in the obese rats. Under these conditions, the liver glycogen store was 45 times higher in the obese than in the lean rats. After 2 days in the cold, liver glycogen store was 4.4 times higher in obese rats than in lean rats. After a 2-day fast in the cold, the liver glycogen store in the obese rats was 30 times higher than in the lean rats. In comparison to fasting at thermoneutrality, fasting in the cold did not lead to a further reduction in hepatic glycogen in obese Zucker rats. The differences observed in the mobilization of the hepatic glycogen store between obese and lean rats have not been found in the mobilization of the carcass glycogen store. Drastic conditions, such as a 2-day fast in the cold, did not exhaust the glycogen store in obese Zucker rats. The present observations point out that obese Zucker rats cannot mobilize the entire hepatic glycogen store, as seen in lean control rats. The role of this abnormality in the high hyperlipogenesis that maintains the obese state is still to be evaluated.

Exercise endurance and fuel utilization: a reevaluation of the effects of fasting.

The effect of fasting on energy utilization during running or swimming was studied in adult male Wistar rats. Compared with fed rats, fasted animals displayed a decreased contribution of carbohydrates in energy supply, with decreased liver and muscle glycogen contents and decreased rate of glycogen breakdown. This was compensated by an enhanced rate of beta-oxidation. In addition, fasting induced an exaggerated sympathoadrenal response during exercise, reflected by a greater epinephrine plasma level and a higher norepinephrine turnover rate in both liver and soleus. Nevertheless, endurance capacity was similar in fasted and fed animals. These results contrast with the impairment of endurance observed in fasting humans but also with the improvement of endurance in rats previously reported by Dohm et al. (J. Appl. Physiol. 55: 830-833, 1983). These data suggest that the metabolic responses to exercise subsequent to food deprivation depend not only on the considered species but also, in the same species (rat), on the age of the animals and the duration of the fast. These factors probably determine the hormonal secretion and substrate utilization during prolonged exercise in fasting conditions.