Gender differences in temperature and vascular characteristics during exercise recovery.

Temperature and vascular responses during exercise recovery were examined in men and women of similar age and fitness status (VO2max: 76 +/- 5 vs 73 +/- 5 mL O2 / kg Fat Free Mass x min). Forearm blood flow (venous occlusion plethysmography; FBF), rectal (Trectal) and forearm skin (Tskin) temperatures (degree C) were measured before and every 15 min up to 105 min (t105) during recovery from a 45-min run at 75% of VO2max. Results indicate Trectal decreased to pre-exercise levels within 25 min in men but reached and remained at values lower than baseline between 60 and 105 min of recovery in women. From 90 to 105 min of recovery, Tskin was lower in women than men (t105 : 29.0 +/- 1.3 vs 30.7 +/- 1.5; p <.05). Recovery FBF (mL/100mL x min) was higher in men than women from the start (6.2 +/- 1.9 vs 4.9 +/- 1.9) to the end of recovery (t105 = 1.7 +/- 0.6 vs 2.6 +/- 1.1) (p <.05). Heat flux calculated at the forearm was higher in women and increased throughout the last hour of recovery (p <.05). Further investigations are needed to examine mechanisms underlying failure of post-exercise core and skin temperatures in women to stabilize at pre-exercise levels.

Oxidation of 13C-glucose and 13C-fructose ingested as a preexercise meal: effect of carbohydrate ingestion during exercise.

The oxidation of 13C-labeled glucose and fructose ingested as a preexercise meal between 180 and 90 min before exercise was measured on 6 subjects when either a placebo or sucrose was ingested during the exercise period. Labeled hexose oxidation, which occurred mainly during the first hour of exercise, was not significantly modified when sucrose was ingested, but exogenous glucose oxidation was significantly higher than exogenous fructose oxidation in both situations. The results suggest that the absorption rate of exogenous hexoses was high when exercise was initiated but diminished thereafter, and that glucose and fructose released from sucrose ingested during exercise did not compete with glucose or fructose ingested before exercise for intestinal absorption, for conversion into glucose in the liver (for fructose), or for uptake and oxidation of glucose in peripheral tissues. However, as already shown, in terms of availability for oxidation of carbohydrates provided by the preexercise meal, glucose should be favored over fructose.

Influence of a transscrotal testosterone propionate administration on the serum level of selected hormones of the hypophyso-gonadal axis.

This study was designed to examine the effect of a percutaneous scrotal administration of testosterone propionate (TP) on selected blood variables, in order to identify a reliable anti-doping probe liable to disclose the illicit use of testosterone. Twelve healthy adult males gave their informed consent for the study. Each morning (8:30) and for 10 consecutive days (D), a placebo (D:1,2,3,...8,9,10) or a testosterone propionate (200mg TP on D:... 4,5,6,7...) scrotal patch was installed. On D2 or D3 (placebo-treated) or D7 (TP-treated), venous blood samples were collected at 5 min intervals from 9:00 until 13:00. Serum LH, FSH, 17alpha-hydroxyprogesterone (17HP), testosterone (T), estradiol (E2) and SHBG contents were analysed by immunoassays. The high sampling frequency revealed that TP was associated with the complete abolition of serum LH pulses. Although statistically significant, TP treatment was not related to explicit changes in serum FSH, E2, T/E2 and T/SHBG. TP-induced effects were most significant on serum LH, T and 17HP and were most clearly illustrated by a bi-dimensional distribution plot of serum values of the latter variables. The expression of a combination of the latter parameters could eventually serve to detect testosterone misusers.

Frequent serum sampling in healthy men discloses testosterone peaks exacerbated by testosterone propionate administration.

Interval samplings uncover blood diurnal oscillations for several hormones, highlighting the importance of short time intervals in the disclosure of subtle pulsatile patterns of some peptide hormones, namely LH. In a study designed to develop new probes against steroid misuse, venous blood was sampled at 5-min intervals for 4 hours from 12 eugonadal adult male athletes, 6 receiving transcutaneous administrations of testosterone propionate and 6 placebo subjects. Brief supraphysiologic serum testosterone peaks were disclosed, the amplitude and frequency of these peaks being larger for the treated group. No solid explanation could be given to explain these bursts. Neither the binding/dissociation kinetics of SHBG molecules with and without increased circulating level of dihydrotestosterone, nor brief testosterone-inducing LH bursts, nor increased Leydig cell release could be invoked to explain these peaks. Their occurrence, although relatively rare, could represent a threat and lead to improper treatment.

Effect of short-term creatine supplementation on renal responses in men.

There is an increasing utilisation of oral creatine (Cr) supplementation among athletes who hope to enhance their performance but it is not known if this ingestion has any detrimental effect on the kidney. Five healthy men ingested either a placebo or 20 g of creatine monohydrate per day for 5 consecutive days. Blood samples and urine collections were analysed for Cr and creatinine (Crn) determination after each experimental session. Total protein and albumin urine excretion rates were also determined. Oral Cr supplementation had a significant incremental impact on arterial content (3.7 fold) and urine excretion rate (90 fold) of this compound. In contrast, arterial and urine Crn values were not affected by the Cr ingestion. The glomerular filtration rate (Crn clearance) and the total protein and albumin excretion rates remained within the normal range. In conclusion, this investigation showed that short-term oral Cr supplementation does not appear to have any detrimental effect on the renal responses of healthy men.

Total fibrin and fibrinogen degradation products in urine: a possible probe to detect illicit users of the physical-performance enhancer erythropoietin?

Erythropoietin (Epo) represents for some athletes the ultimate tool to gain an edge over their peer competitors. Underground information indicates that its usage is spreading at an epidemic pace since no analytical technique is yet available to detect its utilization. We hereby report observations obtained from analysis of urine specimens collected from top-level athletes after international-calibre competitions. Possible Epo misuse was evaluated by the measurement of urine total degradation products (TDPs), excretory fragments attributed by Sakakibara et al. to the fibrinolytic action of Epo. Markedly elevated urine TDP levels were measured in more than 13% of the 76 top-level athletes evaluated in this study. Analyses of urine specimens from a control hockey player group and from out-of-competition resting subjects indicate that the urine TDP content is not significantly influenced by exercise per se. Solid confirmation of TDP measurement as a sound probe to detect illicit Epo users should come from controlled studies with concomitant administration of Epo.

Effects of exercise during normoxia and hypoxia on the growth hormone-insulin-like growth factor I axis.

The response of plasma insulin-like growth factor I (IGF I) to exercise-induced increase of total human growth hormone concentration [hGHtot] and of its molecular species [hGH20kD] was investigated up to 48 h after an 1-h ergometer exercise at 60% of maximal capacity during normoxia (N) and hypoxia (H) (inspiratory partial pressure of oxygen = 92 mmHg (12.7 kPa); n = 8). Lactate and glucose concentrations were differently affected during both conditions showing higher levels under H. Despite similar maximal concentrations, the increase of human growth hormone (hGH) was faster during exercise during H than during N[hGHtot after 30 min: 8.6 (SD 11.4) ng.ml-1 (N); 16.2 (SD 11.6) ng.ml-1 (H); P < 0.05]. The variations in plasma [hGH20kD] were closely correlated to those of [hGHtot], but its absolute concentration did not exceed 3% of the [hGHtot]. Plasma IGF I concentration was significantly decreased 24 h after both experimental conditions [N from 319 (SD 71) ng.ml-1 to 228 (SD 72) ng.ml-1, P < 0.05; H from 253 (SD 47) to 200 (SD 47) ng.ml-1, P < 0.01], and was still lower than basal levels 48 h after exercise during H [204 (SD 44) ng.ml-1, P < 0.01]. Linear regression analysis yielded no significant correlation between increase in plasma [hGHtot] or [hGH20kD] during exercise and the plasma IGF I concentration after exercise. It was concluded that the exercise-associated elevated plasma [hGH] did not increase the hepatic IGF I production. From our study it would seem that the high energy demand during and after the long-lasting intensive exercise may have overridden an existing hGH stimulus on plasma IGH I, which was most obvious during hypoxia.

Effect of metabolic rate on the oxidation of ingested glucose and fructose during exercise.

The purpose of the present study was to describe the relationship between the metabolic rate (W.kg-1 b.m.) and the oxidation rate (mg.kg-1.min-1) of exogenous glucose and fructose during prolonged exercise in 18 healthy active male volunteers (VO2max = 43-71 ml.kg-1.min-1). Each subject performed three 120-min exercises at 60% VO2max (8.5-15.0 W.kg-1.min-1) on cycle ergometer while ingesting water only or 1.33 g.k-1 (97 +/- 9 g; mean +/- SE) of 13C-glucose or 13C-fructose in water (7%). The oxidation rate of exogenous glucose and fructose increased linearly with increasing metabolic rate (r = 0.71 and 0.70, respectively, p < 0.05), the amount of exogenous glucose oxidized being significantly higher than the amount of fructose oxidized (56.1 +/- 14.2 vs 35.7 +/- 9.2 g, respectively). The respective contributions of exogenous glucose and fructose oxidation to the energy yield remain remarkably similar over the range of metabolic rate studied (14.0 +/- 2.1 and 8.9 +/- 1.6%). These observations suggest that the rate of absorption of glucose and fructose and the rate of conversion of fructose into glucose by the liver are not limiting factors for their oxidation, which could simply follow the oxidation rate of circulating glucose. From a practical point of view, these results confirm that fructose is a less efficient energy supplement than exogenous glucose for any metabolic rate sustained.

Respective oxidation of exogenous glucose and fructose given in the same drink during exercise.

We computed the respective amounts of exogenous glucose (G) and fructose (F), which are oxidized during exercise when ingested simultaneously, with the use of 13C labeling. Six subjects exercised for 2 h at 60.7 +/- 2.9% of maximal O2 uptake on a cycle ergometer while ingesting 50 or 100 g of G or F or a mixture of 50 g each of G and F in 500 ml of water. The amount of exogenous G oxidized increased from 37.8 +/- 2.2 to 58.3 +/- 8.1 g when the total amount ingested increased from 50 to 100 g. The amount of F oxidized was significantly lower (32.2 +/- 1.2 and 45.8 +/- 2.6 g for the 50 and 100 g ingested, respectively). When 50 g each of G and F were simultaneously ingested in the same drink, the amounts oxidized (39.5 +/- 4.8 and 34.1 +/- 1.5 g, respectively) were similar to those observed when 50 g of G or F were ingested separately. The cumulative amount of exogenous hexoses oxidized (73.6 +/- 6.6 g) was 21% larger than when 100 g of G were ingested. This finding could be due to the fact that the routes for absorption and metabolism of exogenous G and F are at least partly different, resulting in less competition for oxidation when a mixture of these two hexoses is ingested than when an isocaloric amount of G is ingested. From a practical point of view, these data may provide experimental support for using mixtures of carbohydrates in the energy supplements for endurance athletes.

Method for computing the oxidation of two 13C-substrates ingested simultaneously during exercise.

This study presents a method for computing the respective amounts of two simultaneously ingested exogenous substrates (A and B) that are oxidized during a period of prolonged exercise by use of 13C labeling. This method is based on the observation that the total volume of 13CO2 produced (V13CO2tot) is the sum of 1) V13CO2 arising from the oxidation of endogenous substrates (V13CO2endo), 2) V13CO2 arising from the oxidation of substrate A (V13CO2A), and 3) V13CO2 arising from the oxidation of substrate B (V13CO2B). The equation, V13CO2tot = V13CO2endo+V13CO2A+V13CO2B, with three unknowns, can be solved from the results of three experiments conducted under the same conditions but with at least two values for the isotopic composition of A and B. This method has been used on five healthy male subjects to compute the amounts of glucose and fructose oxidized when a mixture of 15 g of glucose and 15 g of fructose is ingested (in 300 ml of water) over 60 min of cycle ergometer exercise at 65% of maximal O2 uptake. Results from three experiments indicated that 9.8 +/- 3.1 and 5.7 +/- 2.1 g of glucose and fructose, respectively, were oxidized. The total amount of exogenous carbohydrates oxidized (15.5 +/- 4.3 g) is in agreement with the oxidation rates of exogenous glucose computed in similar conditions when 30 g of glucose were ingested (13 g; Péronnet et al. Med. Sci. Sports Exercise 25: 297-302, 1993). The difference between the oxidation rates of exogenous glucose and fructose is also in line with data from the literature.

Effect of plasma prolactin on sweat rate and sweat composition during exercise in men.

We investigated the role of the exercise-induced elevation of plasma prolactin (PRL) concentration on sweat rate and composition during prolonged exercise in men. Two groups of healthy young males (20-26 yr old) showing a high (high responders; n = 8) or a low (low responders; n = 7) response of plasma PRL concentration to exercise were studied during a 60-min period of exercise on a cycle ergometer (65% maximum O2 consumption) in warm conditions (26.2 +/- 0.1 degrees C; 57 +/- 1% relative humidity), 1 h after receiving 1.25 mg bromocriptine (BRC) per os or a placebo. In high responders, administration of BRC totally abolished the threefold increase in plasma PRL observed in response to exercise with placebo [placebo, 10 +/- 2 (rest) and 30 +/- 2 micrograms/l (exercise); BRC, 9 +/- 1 (rest) and 8 +/- 1 microgram/l (exercise)]. The latter was associated with a significant decrease in sweat rate (2.7 +/- 0.5 to 1.9 +/- 0.3 microliter.cm-2.min-1) and a significant increase in sweat Na+ concentration (57 +/- 7 to 68 +/- 5 mmol/l). BRC also reduced the small response in plasma PRL concentration observed in low responders [placebo, 10 +/- 1 (rest) and 15 +/- 1 microgram/l (exercise); BRC, 9 +/- 1 (rest) and 7 +/- 1 microgram/l (exercise)], but this was not associated with any change in sweat rate (2.2 +/- 0.2 to 1.9 +/- 0.3 microliter.cm-2.min-1) or in sweat Na+ concentration (63 +/- 10 to 64 +/- 9 mmol/l).(ABSTRACT TRUNCATED AT 250 WORDS)

A modified, local sweat collector for warm and humid conditions.

The purpose of this study was to modify a previously described local sweat collector to facilitate the investigation of sweat rate and composition in a warm (30 degrees C) and humid (relative humidity 80%) environment. The adherence of the collector to the skin was improved and a pouch was appended at the lower end of the collector. The limitations of the closed collector were examined by comparing the local sweat rate and the quantity of electrolyte excreted in sweat with those obtained using a second collector with a wide opening (to permit free evaporation) and by changes in the body mass. Eight subjects performed exercise on a cycle ergometer consisting of four equal periods of 15 min each, at 60% maximal oxygen consumption, with a rest of 5 min between each period. The sweat produced on a local skin area (85 cm2, upper posterior thorax region) was collected at the end of each period, before measuring the body mass on a sensitive (+/- 1 g) platform balance. The mean local sweat rate [2.61 (SEM 0.19) mg.cm-2.min-1] was 2.4 times greater than the pro-rated whole body mass loss but the two were strongly correlated (r = 0.82, P < 0.01). Compared to the open collector, the greater quantity of electrolyte excreted into the closed collector would suggest that the conditions which prevailed in the closed collector, such as a higher local skin temperature, may have affected the function of the sweat gland.(ABSTRACT TRUNCATED AT 250 WORDS)

Exogenous 13C glucose oxidation during exercise: North American vs Western European studies.

The purpose of this study was to test the hypothesis that the well-documented changes in background 13C enrichment of expired CO2 observed in response to exercise and carbohydrate ingestion, in subjects living on a North American diet, are not present in subjects living on a Western European diet. The experimental protocol used by Pirnay et al. in 1977 and by Krzentowski et al. in 1984 in subjects living on a Western European diet (4 h of exercise on a treadmill at approximately 50% VO2max with ingestion of 100 g of glucose in 400 ml of water) was duplicated as closely as possible in six subjects living on a North American diet. The actual amounts of exogenous glucose oxidized, computed with a high artificial 13C enrichment of glucose (+189.7/1000 delta 13C PDB-1) which allows one to neglect the 1-2/1000 delta changes in 13C background, were [mean (SEM)] 54.7 (5.4) and 84.2 (3.4) g over 2 h and 4 h of exercise, respectively. These values compare well with data computed by Pirnay et al. [56.6 (13.1) and 94.9 (4.2) g] and by Krzentowski et al. [55.0 (6.2) and 88.0 (4.5) g] using a natural enrichment of glucose (-11.21 and -10.63/1000 delta 13C PDB-1, respectively) assuming no change in 13C background in their Western European subjects. Under the same assumption and using a natural enrichment of glucose (-11.30/1000 delta 13C PDB-1) the oxidation of exogenous glucose was overestimated by 30-40% in our North American subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic availability of oral glucose during exercise: a reassessment.

The purpose of this study was to reassess the metabolic availability of oral glucose during prolonged exercise in man, using 13C-labeling and a computation procedure (J Appl Physiol 69:1047-1052, 1990) that correctly takes into account changes in isotopic composition of CO2 arising from oxidation of endogenous substrates (Rendo). These changes are due to glucose ingestion associated with exercise. Each of the seven subjects completed three 2-hour periods of exercise at 67% maximum oxygen consumption (VO2max) on an ergocycle, with ingestion of water (1,000 mL) or 60 g (in 1,000 mL water) of 13C-labeled glucose at two levels of enrichment (13C/12C = 1.11482% and 1.13303%). As expected, Rendo significantly increased from rest to exercise with water ingestion (1.09888% +/- .00196% to 1.09970% +/- .00175%) and with glucose ingestion (1.10002% +/- .00159%) due to changes in the respective contributions of endogenous carbohydrates and fat to energy requirements as assessed by the respiratory exchange ratio (RER). When changes in Rendo were taken into account, the estimated amount of exogenous glucose oxidized was 38.8 +/- 10.3 g. Much higher values were found when Rendo at rest or during exercise with water ingestion were used in the computation (42.3 +/- 10.3 to 65.1 +/- 20.5 g) according to the commonly used method. Examination of data in the literature indicates that the reported oxidation rate of exogenous glucose (g/min) is significantly related to oxygen consumption (VO2) (L/min; r = .592) and that exogenous glucose contributes approximately 14% to 17% to the energy requirement.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxidation of exogenous medium-chain free fatty acids during prolonged exercise: comparison with glucose.

The purpose of this study was to compare the oxidation rate of exogenous 13C-labeled medium-chain triacylglycerols (MCT) with that of an isocaloric amount of exogenous [13C]glucose and to evaluate their respective effects on endocrine and metabolic responses to moderate prolonged exercise. To take into account changes in isotopic composition of 13CO2 arising from oxidation of endogenous substrates because of exercise and/or substrate ingestion that overestimates the oxidation rate of exogenous substrates, two levels of 13C enrichment were used for each substrate. Six young healthy males (20-26 yr of age) completed five 2-h periods of exercise at 65 +/- 3% maximal O2 uptake (VO2max) on a cycle ergometer at 7-day intervals: one control exercise with water ingestion, two trials with ingestion of 25 g of [13C]MCT (trioctanoate) 1 h before exercise, and two trials with 57 g of [13C]glucose (dissolved in 1,000 ml of water) ingested during exercise. Exogenous MCT and glucose began to be oxidized within the first 30 min of exercise, and the oxidation rate increased progressively until the end of exercise for both substrates. Over the 2-h period of exercise, 13.6 +/- 3.5 g of ingested MCT and 36.4 +/- 8.2 g of exogenous glucose were oxidized, which represent 54 and 64%, respectively, of the total amount ingested. The contribution of MCT (119 +/- 31 kcal) and glucose (140 +/- 36 kcal) was not significantly different and represented 7 and 8.5%, respectively, of the total energy expenditure.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute administration of bromocriptine abolishes the hyperprolactinemic response induced by submaximal exercise in man.

The effective control of hypophysial prolactin (PRL) secretion with a pharmacological agent is a prerequisite for the investigation of the role of hyperprolactinemia observed during exercise. Using bromocriptine, a potent inhibitor of PRL secretion, this study established the proper experimental conditions whereby any significant increase in plasma PRL level can be prevented and basal circulating levels maintained during physical exercise. On three occasions at weekly intervals, 15 male adults, separated into two groups, exercised on an ergocycle (40 min at 65% VO2max) either 1 or 3 h after ingesting either placebo or 1.25 or 2.50 mg of bromocriptine mesylate (Parlodel; Sandoz Canada Inc., Dorval, Qué.). Under all conditions, the plasma PRL elevation observed during exercise after placebo was prevented by the administration of bromocriptine. Resting plasma PRL levels were maintained when exercise was performed 1 h after bromocriptine ingestion, but were significantly reduced when exercise was performed 3 h after administration of either bromocriptine dosages. Considering the primary and secondary effects observed, 1.25 mg of bromocriptine administered 1 h before exercise provides suitable experimental conditions to investigate the role of the increase in plasma PRL during physical exercise.