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.

Whole body and muscle respiratory capacity with dobutamine and hindlimb suspension.

The effects of repeated injections of dobutamine, a synthetic catecholamine, were studied in control and tail-suspended rats to determine whether this drug could improve the metabolic response to unweighting. Dobutamine prevented the decrease in maximal oxygen uptake (VO2max) induced by hindlimb suspension. Furthermore, VO2max was 12% greater in dobutamine-treated animals than in saline-treated control animals. Soleus muscle weight and mean fiber cross-sectional area were decreased by 60 and 75%, respectively, in saline- and dobutamine-treated suspended rats. Total capillary length was unaffected by unweighting and increased 21% in all animals receiving dobutamine. The drug prevented the increase in total mitochondrial volume density (+30%) induced by unweighting but did not change total mitochondrial volume. Our results suggest that 1) dobutamine is useful to prevent the decrease of total aerobic capacity during hindlimb suspension, 2) dobutamine increases VO2max in control rats, and 3) total capillary length in soleus muscle is increased by the drug in all groups, although no beneficial effects on mitochondria can be detected.

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)

Effect of spontaneous recovery or retraining after hindlimb suspension on aerobic capacity.

The purpose of this study was to compare the effects of spontaneous recovery or recovery by treadmill training (180 min/day, 5 days/wk, 30 m/min for 8 wk) on maximal O2 uptake (VO2max), histochemical and biochemical muscular properties (soleus), of rats subsequent to 5 wk of hindlimb suspension. Spontaneous recovery reversed the 15% reduction in VO2max, whereas training posthypokinesia induced a 20% increase over control values. In the spontaneous recovery group, both citrate synthase and 3-hydroxyacyl-CoA dehydrogenase activities, decreased by hypokinesia (-40%), increased but remained 20% below the control level. In the training posthypokinesia group, an increase of these activities over control occurred (+50 and +20%, respectively). Recovery or training led to a 100% type I distribution in soleus muscle and to a recovery of all fibers' cross-sectional areas. In the spontaneous recovery group, capillaries per fiber, decreased by 46%, returned to the normal range. In the training posthypokinesia group, training induced an increase in capillaries per fiber above their control values (+23%). These results point to the plasticity of the muscle and indicate the necessity of a posthypokinesia training program for recovery of the total oxidative enzyme capacity.

Rat soleus muscle ultrastructure after hindlimb suspension.

The aim of the present investigation was to determine, by quantitative electron microscopy, the effects of a 5-wk tail-suspension period on rat soleus muscle ultrastructure. A marked decline (-60%) in muscle mass occurred. The mean fiber cross-sectional area decreased to a greater extent (-75%) than the capillary-to-fiber ratio (-37%), leading to a higher capillary density (+148%) after hypokinesia. The total mitochondrial volume density remained unchanged, whereas the volume density of myofibrils was slightly but significantly reduced (-6%). A shift from subsarcolemmal to interfibrillar mitochondria occurred. Interfibrillar mitochondrial volume density was highest near the fiber border and decreased toward the fiber center. An increase in volume density of satellite cells suggested muscle regenerative events. Soleus atrophy with tail suspension greatly decreases the muscular volume but leaves the ultrastructural composition of muscle fibers relatively unaffected.

Additive effects of training and high-fat diet on energy metabolism during exercise.

This study was conducted to obtain additional information about the adaptations after 12 wk of high-fat diet (HFD) per se or HFD combined with endurance training in the rat using a two [diet: carbohydrate (CHO) or HFD] by two (training: sedentary or trained) by two (condition at death: rested or exercised) factorial design. Adaptation to prolonged HFD increases maximal O2 uptake (VO2max; 13%, P less than 0.05) and submaximal running endurance (+64%, P less than 0.05). This enhancement in exercise capacity could be attributed to 1) an increase in skeletal muscle aerobic enzyme activities (3-hydroxyacyl-CoA dehydrogenase and citrate synthase in soleus and red quadriceps) or 2) a decrease in liver glycogen breakdown in response to 1 h exercise at 80% VO2max. When training is superimposed to HFD, the most prominent finding provided by this study is that the diet-induced effects are cumulative with the well-known training effect on VO2max, exercise endurance, oxidative capacity of red muscle, and metabolic responses to exercise, with a further reduction in liver glycogen breakdown.

Structural and functional responses to prolonged hindlimb suspension in rat muscle.

The purpose of this study was to investigate alterations in structural and functional properties in the soleus (SOL) and extensor digitorum longus (EDL) muscles of rats after 1, 2, and 5 wk of tail suspension. Maximal O2 uptake was 19% lower after 5 wk suspension. Loss of muscle mass was greater in SOL (63%) than in EDL (22%) muscle. A reduction of type I distribution was accompanied by an increase of intermediate fiber subgroups (int I in SOL, int II in EDL). The cross-sectional area of all three fiber types was reduced by hypokinesia. The decrease in capillaries per fiber in SOL was greater than the decrease in citrate synthase and 3-hydroxyacyl-CoA dehydrogenase activities after 5 wk. No alteration in lactate dehydrogenase activity was noted. In EDL, no changes in fiber area, capillarization, and enzymatic activities occurred. Energy charge remained unchanged (0.91) whatever the muscle. These results suggest that type I fibers showed an earlier and greater susceptibility than type II fibers to suspension which is also accompanied by a decreased aerobic capacity.

Effects of gluconeogenic precursor flux alterations on glycogen resynthesis after prolonged exercise.

The importance of gluconeogenic substrates (i.e., lactate, glycerol, and alanine) in the glycogen resynthesis observed in fasting rats after exhausting submaximal exercise [R.D. Fell et al. Am. J. Physiol. 238 (Regulatory Integrative Comp. Physiol. 7): R328-R332, 1980] was examined in muscles and liver in response to pharmacological alterations of gluconeogenic precursor flux. The minor role of lactate for glycogen resynthesis after prolonged submaximal exercise was confirmed by the insignificant accumulation of lactate neither in muscles nor in plasma. When the rate of lipolysis is reduced either by beta-blockade or by nicotinic acid injection, the replenishment of muscle glycogen persisted, suggesting that glycerol released by triglycerides hydrolysis did not play an important role in glycogen resynthesis. On the other hand, when pyruvate oxidation is enhanced by dichloroacetate (DCA), thus reducing plasma levels of lactate and alanine, glycogen resynthesis was completely blocked in liver and partly in some but not all muscles. This failure in total inhibition of glycogen resynthesis associated with the significant reduction of the plasma alanine level could be attributed to the possible stimulation of gluconeogenesis from alanine by DCA (R.A. Harris and D.W. Crabb. Arch. Biochem. Biophys. 189: 364-371, 1978). The results could point out alanine as the major gluconeogenic substrate during recovery from exhaustive exercise in fasting conditions.

Fluid regulatory hormone response to exercise after coca-induced body fluid shifts.

To determine the effect of coca chewing on heart rate (HR), mean arterial blood pressure (MAP), and plasma volume and their relationship with the hormones regulating cardiovascular and body fluid homeostasis, 16 male volunteers were examined at rest and during 1 h of cycle exercise at approximately 75% of their peak oxygen uptake in two trials separated by 1 mo. One trial was performed after the subjects chewed a sugar-free chewing gum (Coca- trial), whereas the other was done after the subjects chewed 15 g of coca leaves (Coca+), with the order of the Coca- and Coca+ trials being randomized. Blood samples were taken at rest, before (R1) and after 1-h chewing (R2), and during the 5th, 15th, 30th, and 60th min of exercise. They were analyzed for hematocrit, hemoglobin concentration, red blood cell count, plasma proteins, and for the fluid regulatory hormones, including plasma catecholamines [norepinephrine (NE) and epinephrine], renin, arginine vasopressin, and the atrial natriuretic peptide (ANP). During the control trial (Coca-), from R1 to R2, there was no significant change in hematologic, hormonal, and cardiovascular status except for a small increase in plasma NE. In contrast, it can be calculated that coca chewing at rest induced a significant hemoconcentration (-3.8 +/- 1. 3% in blood and -7.0 +/- 0.7% in plasma volume), increased NE and MAP, and reduced plasma ANP. Chewing coca before exercise reduced the body fluid shifts but enhanced HR response during exercise. These effects were not accompanied by changes in NE, epinephrine, renin, and arginine vasopressin plasma levels. In contrast, plasma ANP response to exercise was lower during the Coca+ trial, suggesting that central cardiac filling was reduced by coca use. It is likely that the reduction in body fluid volumes is a major contributing factor to the higher HR at any given time of exercise after coca chewing.

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.

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.

Skeletal muscle adaptation in rats flown on Cosmos 1667.

Seven male Wistar rats were subjected to 7 days of weightlessness on the Soviet biosatellite Cosmos 1667. Muscle histomorphometry and biochemical analyses were performed on the soleus (SOL) and extensor digitorum longus (EDL) of flight rats (group F) and compared with data from three groups of terrestrial controls: one subjected to conditions similar to group F in space except for the state of weightlessness (group S) and the others living free in a vivarium (V1, V2). Relative to group V2 (its age and weight-matched control group), group F showed a greater decrease of muscle mass in SOL (23%) than in EDL (11%). In SOL a decrease in the percentage of type I fibers was counterbalanced by a simultaneous increase in type IIa fibers. The cross-sectional area of type I fiber was reduced by 24%. No statistically significant difference in capillarization and enzymatic activities was observed between the groups. In EDL a reduction in type I fiber distribution and 3-hydroxyacyl-CoA-dehydrogenase activity (27%) occurred after the flight. The small histochemical and biochemical changes reported suggest the interest in studying muscular adaptation during a flight of longer duration.

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.

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.

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.

Radioimmunoassay of arginine vasopressin, oxytocin and arginine vasotocin-like material in the human pineal gland.

Specific radioimmunoassays (RIAs) have been developed for arginine-vasopressin (AVP), oxytocin (OT), and arginine-vasotocin (AVT): they can detect 2.5 pg, 5 pg and 1 pg of hormone respectively. The three antisera employed in the RIAs in the present study all had a specificity that discriminated between the three neuropeptides and thus allowed their accurate measurement in each of 157 human pineal glands. Immunoreactive AVP was found to have a mean concentration of 306.4/+-27.6 (SE) pg/gland in the 1389 pineals where it was at level higher than the detection limit. Immunoreactive OT was determined as 386.3/+-42.1 pg/gland in the 110 pineals where it was measurable, and the mean apparent immunoreactive AVT content was 44.6/+-3.6 pg/gland in the 110 pineals where it was found at detectable levels. Cross-reactivity with AVP or OT cannot account for the immunoreactive peptide content of human adult pineal glands was demonstrated as a function of: (1) sex, (2) time of death, (3) cause of death, (4) age (18 to 85 yr old) or (5) delay between death and gland removal over the range of 4 to 48 hr. While the presence of AVP and OT is not surprising, indications of an immunoreactive AVT may in fact reflect a peptide which is closely related to AVT and cross-reacts in the AVT RIA.

Presence of neurophysins I and II in the human pineal gland: comparison with the content of neurohypophyseal hormones.

We have previously measured the individual content of immunoreactive vasopressin (AVP), oxytocin (OT) and vasotocin (AVT) in 155 human pineal glands, and report here identification and measurement of the neurophysin (Np) content of the same glands, using specific homologous human neurophysin I (HNp I) and neurophysin II (HNp II) radioimmunoassays. Median values for HNp I were for men 47 ng/gland (range, 5 to 1360) and for women 24 ng/gland (range, 5 to 1000); median values for HNp II were respectively 7 ng/gland (range, 2 to 191) and 15 ng/gland (range, 2 to 356) with no significant difference between men and women for HNp I and HNp II but a significant difference (p less than 0.001) between HNp I and HNp II for both sexes. Gel filtration showed that pineal neurophysins were eluted at the same volume as both standard Np and Np from human posthypophyses used as controls. HNp I correlated both with AVP (rs = 0.54 for men and 0.55 for women) and OT (rs = 0.86 for men and 0.57 for women) but not with AVT, while HNp II correlated with AVP (rs = 0.52 for men and 0.53 for women) and OT (rs = 0.92 for men and 0.50 for women) but not with AVT. This study thus confirms the presence of two neurophysins in the human pineal gland and further indicates that they are related to AVP and OT concentrations in the same gland. The results also imply, however, that the presence of immunoreactive AVT (more probably a closely related peptide) is independent of the neurophysins.

[Radioimmunoassay of ADH in human urine (author's transl)]. / Dosage radioimmunologique de L'ADH dans les urines chez l'homme.

A simple efficient procedure for extracting and concentrating arginine-8-vasopressin (AVP) from urine has been coupled with a specific and sensitive radioimmunoassay in order to measure antidiuretic hormone (ADH) excretion in normal humans under various physiological stimuli. Antisera have been raised in rabbits injected with lysine-vasopressin (LVP) or AVP coupled with bovine serum albumin. The antiserum selected for the assay which inhibits the antidiuresis induced in the rat by AVP is used at a final dilution of 1 : 50,000 and possesses a high association constant of 1 x 10(11) 1.mol-1. The limit of detection of the RIA system is 0.5 micronUI/ml of urine (1.25 pg). Urinary ADH has been extracted from urine by Miller and Moses method. Mean recovery of added vasopressin averaged 90.2% +/- 11 (SD) and assay of serial dilutions of such extracts showed that they behave in the assay system in the same way as synthetic AVP standards. Moreover comparison of the results obtained by the RIA to those given by the biological method using the ethanol anesthetized rat showed excellent correlation (r = 0.9 p less than 0.001). Under ad libitum fluid and food intake, mean daily urinary excretion of AVP (uncorrected for recovery) determined in 22 subjects was found to be 30.58 +/- 11.64 mU/h with no significant difference between men and women. In response to an oral waterload ADH became undetectable at the peak of diuresis. Following a 16 hr fluid deprivation, ADH rose moderately. A significant correlation has been found between urine osmolality and AVP excretion rate.