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Biomedical subjects

G Pérès

Publications and source records attributed to G Pérès.

At least 19 recordsLinked to original sources
PubMed2001

Wintertime vitamin D deficiency in male adolescents: effect on parathyroid function and response to vitamin D3 supplements.

The first part of this study consisted of an 18 month follow-up of the vitamin D status and parathyroid function in a group of 54 French male adolescents, aged from 13 to 16 years old and all pupils of a jockey training school. During the 18 month period four samplings were made, one every 6 months. The first was during September of the first year, the second and third during March and October of the second year, and the last in March of the third year. Therefore we had two main periods: summer and winter. The summer 25-hydroxyvitamin D (25(OH)D) concentrations were higher (71.6 +/- 19.9 and 52.4 +/- 16.5 nmol/l) than the winter ones (20.4 +/- 6.9 and 21.4 +/- 6.1 nmol/l). Conversely, the winter intact parathyroid hormone (iPTH) serum levels (4.18 +/- 1.18 and 4.11 +/- 1.35 pmol/l) were higher than the summer ones (2.44 +/- 0.82 and 2.71 +/- 0.71 pmol/l). At the two winter time points the 25(OH)D concentrations were lower than 25 nmol/l (10 ng/ml) in 72% (2nd year) and 68% (3rd year) of the adolescents. In the second part of the study we tried a vitamin D3 supplementation procedure designed to maintain the 25(OH)D and iPTH postsummer serum levels throughout the winter. Pairs of male adolescents matched for height, weight and Tanner pubertal stage were randomly assigned to either vitamin D3 supplementation (2.5 mg, i.e., 100,000 IU) administered orally at three specific periods (end of September, November and January) or no vitamin D3 treatment (control subjects). Blood was collected just before the first intake of vitamin D3 and 2 months after the last intake (March). The control subjects had blood drawn at the same time points. In the vitamin D3-treated subjects, the concentrations of 25 (OH)D (55.3 +/- 11.5 nmol/l) and of iPTH (3.09 +/- 1.16 pmol/l) in March and September (53.8 +/- 12.3 nmol/l and 2.75 +/- 1.26 pmol/l) were not significantly different. In the control subjects, March 25(OH)D levels (21.0 +/- nmol/l were low, with values below 25 nmol/l in 78% of subjects, and iPTH concentrations (3.97 +/- 1.08 pmol/l) were significantly (p<0.001) higher than in September (2.91 +/- 0.81 pmol/l). The constant vitamin D wintertime deficiency and wintertime rise in iPTH in adolescent French males throughout puberty has been demonstrated. In adolescents with low dairy calcium intakes, the vitamin D3 treatment was sufficient to maintain 25(OH)D concentrations at their summer levels throughout winter and to prevent an excessive wintertime rise in iPTH levels.

Adolescent↗
PubMed2001

Does perceived exertion depend on glycemic index of foods ingested throughout three hours before a one-hour high-intensity exercise?

The purpose of this study was to assess the relationships between perceived exertion (RPE) and plasma glucose concentrations or hunger feelings during a 1-hr. bicycle submaximal exercise after ingestion of pre-exercise test foods with a different glycemic index. Each of endurance-trained male triathletes ingested three different glycemic index (GI) foods (HighGI: glucose, LowGI: whole-wheat biscuit or water) throughout the 3 hr. before exercise at 80% maximal oxygen uptake (VO2 max). RPE values increased as a logarithmic function of time. This result is opposite to results obtained with longer exercise bouts up to 3 hr. duration. RPE and hunger ratings were not significantly different for the three test foods whatever the time. Moreover, RPE did not correlate with plasma glucose concentrations during exercise. Consequently, RPE did not depend on the GI of the pre-exercise test foods during a 1-hr. exercise at 80% VO2 max. Physiological and psychological factors other than glycemic index may have mediated the perceptual responses during a 1-hr. high-intensity exercise. It is possible that during endurance exercise of longer duration, the level of blood glucose mediates the intensity of peripheral exertional perceptions arising from active skeletal muscle during prolonged exercise.

Adult↗
PubMed1999

Vitamin D status during puberty in French healthy male adolescents.

The vitamin D status was determined on one to four occasions either after summer (September-October) or after winter (March-April) in 175 male adolescents (13-17 years), resulting in 394 measurements of serum 25-hydroxyvitamin D (25(OH)D) and intact parathyroid hormone (iPTH). The subjects lived in a rural area to the north of Paris (49 degrees N). After summer the 25(OH)D concentration was 58.5 +/- 18.0 nmol/l (mean +/- SD), while after winter it had fallen to 20.6 +/-6.0 nmol/l (p = 0.0001). Meanwhile the iPTH concentration was 2.76 +/- 0.97 pmol/l (mean +/- SD) after summer and increased to 4.20 +/- 1.21 pmol/l after winter (p = 0. 0001). All the results were pooled and a nonlinear population model with random parameters was used to describe the relationship between serum iPTH and 25(OH)D. When the concentration of 25(OH)D was higher than 83 nmol/l, an iPTH mean 'plateau' level at 2.48 pmol/l was reached. When 25(OH)D concentrations fell below 83 nmol/l, the increase in iPTH concentration accelerates, and when the mean 25(OH)D concentration was equal to or lower than 10 nmol/l the mean iPTH level (4.97 pmol/l) was twice as high as the 'plateau' value.

Adolescent↗
PubMed1998

Oral administration of dehydroepiandrosterone to healthy men: alteration of the urinary androgen profile and consequences for the detection of abuse in sport by gas chromatography-mass spectrometry.

Dehydroepiandrosterone (DHEA) replacement therapy as compensation for high age-related decline of DHEA and DHEA sulfate production is a matter of intense investigation, since many beneficial effects have been proven, or are suggested and expected. Therefore, DHEA abuse by athletes has been considered by the International Olympic Committee, which banned the substance recently. As DHEA for oral supplementation is easily available, we decided to investigate the effect on the urinary androgen profile of administration along this route of a single substitution dose of 50 mg. Quantitative analysis by gas chromatography-mass spectrometry with selected ion monitoring demonstrated that the drug was readily absorbed with 50 to 75% recovery of dosing after 24 h, and with glucuro- and sulfoconjugates of DHEA, androsterone, and etiocholanolone as the most abundant metabolites. In agreement with reported data found in blood, conversion of exogenous DHEA to the principal biologically active androgen, testosterone, was low but proven to be real by the administration of deuterium-labeled DHEA and the subsequent identification and quantification of deuterium-labeled testosterone. A concentration threshold of 300 micrograms/L of DHEA glucuronide is proposed for the screening of DHEA abuse in sport, but a single replacement dose can only be detected during 8 h. Such a short detection period is the consequence of considerable first-pass hepatic metabolism and also of the high interindividual variability of circulating and urinary DHEA and DHEA sulfate concentrations.

Adult↗
PubMed1998

[Vitamin D status in the adolescent: seasonal variations and effects of winter supplementation with vitamin D3].

BACKGROUND: Recently, 25 hydroxyvitamin D (25 OHD) blood concentrations measured in adolescents during or at the end of winter were found very low. A concomitant stimulation of parathyroid function was observed. The aim of the present study was to test the biological effects of a treatment with vitamin D3 during winter. POPULATIONS AND METHODS: The effects of vitamin D3 supplementation (100,000 IU, twice, at the end of November and of January) were assessed in 24 male Caucasian adolescents (mean age +/- SD: 14 y 6 m +/- 9 m). They were pupils in a lad-jockeys training center located in the countryside near Chantilly (49 degrees northern latitude). Blood concentrations of 25 OHD, calcium and intact parathormone (PTH) were measured three times: before each oral intake of vitamin D3 and 2 months after the last intake (March). A group of 32 male adolescents (mean age +/- SD: 14 y 9 m +/- 6 m), pupils in the same center, receiving no vitamin D and sampled in November and in March, served as controls. RESULTS: In March, mean concentrations of 25 OHD (8.36 +/- 2.73 micrograms/L) were very low in vitamin D-not supplemented adolescents since 34% had levels less than 6 micrograms/L. In March, PTH concentrations (40.5 +/- 12.2 ng/L) were significantly (P = 0.0001) higher than in November (28.8 +/- 9.9 ng/L). In boys receiving vitamin D3 25 OHD serum concentrations measured in January (17.5 +/- 3.2 micrograms/L) and in March (18.7 +/- 4.0 micrograms/L) remained at a level not very different from that measured in November (16.6 +/- 3.8 micrograms/L). During the same period, calcium and PTH concentrations (32.2 +/- 11.7 ng/L in November; 32.4 +/- 14.3 in January and 32.9 +/- 13.5 ng/L in March) remained at their basal level as well. CONCLUSIONS: The observation that, after winter, a relatively large number of adolescents presented low concentrations of 25 OHD suggests that, during winter, usual dietary intakes and/or vitamin D stores are not sufficient to provide for their needs. Administration of two oral doses of 100,000 IU of vitamin D3 could maintain the vitamin D status at its initial level. The efficiency of such a prophylactic treatment is also assessed by its effect on parathyroid function.

Adolescent↗
PubMed1996

The relationship between maximal power and maximal torque-velocity using an electronic ergometer.

Eight subjects performed a single allout sprint on a cycle ergometer with strain gauges bonded to the cranks. The crank angle-torque curves of the left and right legs were recorded during ten revolutions using the software package supplied with the ergometer. Torque data were stored every 2 degrees (180 angletorque data per pedal revolution for each leg). The ergometer was used in the linear mode with the lowest available linear factor (F1 = 0.01). In this mode, the braking torque (TB) was proportional to cycling velocity v(TB = F1v) and mechanical power was equal to F1v2. The relationship between the torque averaged over one revolution and the average velocity of one pedal revolution was studied during the acceleration phase of short allout exercise on an electronic ergometer (eight subjects) and a friction-loaded ergometer (four subjects). The present study showed that it is possible to determine the maximal torque-velocity relationship and to calculate maximal anaerobic power during a single allout sprint using an electronic cycle ergometer provided that strain gauges are bonded to the cranks. The torque-velocity relationships calculated were linear as for a friction loaded ergometer. As expected, the values of torque and maximal power measured with the strain gauges were higher than the corresponding values computed from the data collected during an allout test on a friction loaded ergometer. The torque-angle data collected during a single allout cycling exercise would suggest that angular accelerations of the leg segments and gravitational forces play the main role at high velocity.

Adult↗
PubMed1996

Plasma and urinary markers of oral testosterone misuse by healthy men in presence of masking epitestosterone administration.

There is a potential need for the official criterion of testosterone abuse in sport (the urinary concentration ratio of testosterone glucuronide/epitestosterone glucuronide, TG/EG > 6) to be backed-up by some complementary markers, more particularly in cases of physiologically high TG/EG and when there is suspicion of joint administration of testosterone and epitestosterone. Testosterone, epitestosterone, their glucuro- and sulfoconjugates, 5-androstene-3 beta, 17 alpha-diol glucuronide and 17-hydroxyprogesterone have been analysed by isotope dilution-gas chromatography-mass spectrometry in plasma and urine of seven subjects supplemented with a single oral dose of undecanoates of testosterone and epitestosterone (respectively 40 mg and 1.5 mg). Adequate plasma criteria for testosterone abuse were the ratios of testosterone glucuronide/17-hydroxyprogesterone and testosterone glucuronide/testosterone which increased significantly above basal values for up to 10 h. The same trend was observed for the ratio of urinary glucuronides of testosterone/5-androstene-3 beta, 17 alpha-diol, while TG/EG was not affected by simultaneous administration of epitestosterone. One subject with low basal TG/EG failed to respond to testosterone administration by any significant increase of analysed parameters.

Adult↗
PubMed1994

Urinary profile of androgen metabolites at different stages of pubertal development in a population of sporting male subjects.

In this cross-sectional study on 140 subjects, several testosterone and epitestosterone metabolites have been analyzed by gas chromatography-mass spectrometry associated with stable isotope dilution, a technique requested for doping analysis in general, and detection of exogenous testosterone supply in particular. Urinary excretions of luteinizing hormone, testosterone and epitestosterone glucuronides and sulfates, as well as glucuronides of 5-androstene-3 beta, 17 alpha-diol, 5 alpha- and 5 beta-androstane-3 alpha, 17 alpha-diol and the corresponding 17 beta-isomers, present similar patterns of increase throughout pubertal development, from stage 1 up to stage 5. Excretion levels are significantly different in general between stages 1, 2, 3 and 4, the highest percentage increase being observed between stages 3 and 4. None of the ratios of testosterone to epitestosterone glucuronides are beyond the threshold value of 6, where testosterone abuse by athletes is suspected. No particular pubertal stage exceeded this critical value with a probability higher than p = 0.006, a value that was determined on the whole population. This is consistent with the non-significant differences between correlation slopes of regression curves, relating either testosterone or epitestosterone glucuronide to chronological age. The ratio of testosterone glucuronide to luteinizing hormone increases significantly throughout puberty and this might be a limitation to the widespread use of this ratio for the detection of testosterone misuse.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

The comparison of the effects of heavy metal ions on the antioxidant enzyme activities in human and fish Dicentrarchus labrax erythrocytes.

1. The effect of the increasing concentrations of CuSO4 and HgCl2 (0.01-0.3 mmol/l) on erythrocyte haemolysis and the activities of peroxide metabolism enzymes: superoxide dismutase, catalase, peroxidase and glutathione peroxidase was investigated in human erythrocytes and the nucleated red blood cells of marine fish (Dicentrarchus labrax). 2. The results show that both heavy metal ions had only little effect on haemolysis and antioxidant enzyme activities in human erythrocytes; in contrast the effect of heavy metals on fish erythrocytes was statistically significant when compared to control values. 3. Copper was found to have more pronounced effect than mercury on the erythrocytes of Dicentrarchus labrax; otherwise there were no significant differences between the toxic effects of both ions on human erythrocytes. 4. We suggest that the mechanism of copper-induced haemolysis may be different from that of mercuric ion in the erythrocytes of Dicentrarchus labrax.

Animals↗
PubMed1989

The effect of MS 222 an anaesthetic on the peroxide metabolism enzymes in erythrocytes of freshwater and marine fish species.

1. The effect of 70 mg/l and 35 mg/l MS 222 an anaesthetic on the enzymes: superoxide dismutase (SOD), catalase (C) and peroxidase (P) were estimated in erythrocytes of Cyprinus carpo, a freshwater fish and Dicentrarchus labrax, a marine fish. 2. The end of the summer, at 16 degrees C MS 222 in concentration 70 mg/l caused an enhancement of the SOD and peroxidase activities and a decrease of the catalase activity. 3. In the autumn at 22 degrees C SOD and peroxidase activities in erythrocytes of Dicentrarchus labrax are normally higher than at 16 degrees C. On the contrary MS 222 causes no significant modification of enzymatic activities measured, but an increase in the dispersion of the results. 4. At 13 degrees C in the spring, MS 222 has no immediate influence on the activity of these enzymes, whilst at the same temperature at the beginning of winter, SOD is the only one activated. 5. It seems that in experiments concerning peroxide metabolism enzymes the use of anaesthetic MS 222 is not advisable.

Aminobenzoates↗
PubMed1989

Force-velocity relationship and maximal anaerobic power during cranking exercise in young swimmers.

To study the effect of growth upon maximal anaerobic power of the upper and lower limbs, the maximal power developed during a cranking force-velocity test was correlated with the height of a vertical jump in different age groups of young swimmers. The youngest swimmers were significantly less powerful than the oldest. Differences in body size partly accounted for the differences in maximal power during cranking exercise (Wmax = 0.31 + 0.048 age; r = 0.526; P less than 0.01; where Wmax was expressed in W.kg BM-1 and age in months; n = 103). The effect of growth upon vertical jump is similar to the effect upon maximal cranking power: the lowest values were similar to those which concerned Wmax.kg-1. There was a very significant correlation between Wmax in cranking (in W.kg-1) and the height of the vertical jump (VJ in cm) (Wmax = 1.15 + 0.145 VJ; r = 0.728; n = 103, P less than 0.01).

Adolescent↗
PubMed1987

Relationships between individual isometric muscle forces, EMG activity and joint torque in monkeys.

The aim of the present work was to determine the EMG activity and the moment of force developed by the main elbow flexor muscles, and to establish on this basis the degree of their participation in isometric contractions performed at various positions of the elbow. This was achieved by recording the following biomechanical parameters: EMG and tensile stress (or force) from biceps brachii (BB) and brachioradialis (BR); EMG from brachialis; external resultant force (FE). There was: a linear or quadratic relationship between the integrated EMG from each muscle and FE; a linear relationship between the force produced by BB or BR and FE. The slope of these relationships depended on the elbow angle, except for that between BB force and FE. It is proposed that iEMG changes compensate for those of the force lever arm. It has been calculated that the contribution of BR to external torque decreased from the extension to flexion while that of BB increased from 70 degrees to 90 degrees and then decreased. How far these data can be extrapolated to man is a matter of discussion based on iEMG and anthropometrical data.

Animals↗
PubMed1987

[In vivo determination of alkaline phosphatase activity of the intestine of the rainbow trout (Salmo gairdneri R.)].

This work has concerned the description of a method suitable for the measurement, on living trout, of the intestinal alkaline phosphatase activity. The experiments consist in the perfusion, in the lumen, of an appropriate substrate and in the prevention of its absorption or that of the products of its hydrolysis. This condition has not been satisfied by using paranitrophenyl phosphate which has been replaced by glucose-1-phosphate. The absorption of glucose produced has been inhibited by phloridzin (10(-4) M) in a KCl (150 mM) solution. Under these conditions an hydrolysis of glucose phosphate has been shown at alkaline pH, which remains linear with time up to 60 min. A research of the Km of the enzyme activity has been carried out.

Alkaline Phosphatase↗
PubMed1986

Comparative antioxidant enzyme and lipid peroxidation study in erythrocytes and liver of some freshwater fish.

1. Superoxide dismutase (SOD), catalase (C), peroxidase (P) and glutathione peroxidase (GSH-Px) were estimated in the erythrocytes and liver of the carp, the tench and the crucian carp during a two-years period, 1983-1984 (autumn). 2. The lipid peroxidation (LP) of the erythrocytes and liver homogenates was also compared. 3. The activities of the enzymes examined showed significant interspecies variations. 4. Significant differences were observed between enzyme activities (except for SOD in the liver) and lipid peroxidation in erythrocytes and liver of investigated fish species. 5. The very high values of peroxide enzyme activities in fish erythrocytes and SOD in fish liver suggest the predominant role of these enzymes in protection of polyunsaturated acids against uncontrolled oxidative processes.

Animals↗
PubMed1986

[Maternal and fetal heart rates during bicycle ergometer exercise].

The cycle ergometer (an exercise cycle) Monark was used to study the repercussions on the fetus of physical exercises carried out by the mother at the end of pregnancy (after 37-39 weeks of amenorrhoea). The maternal and fetal heart rates were measured at the same time while the mother was pedalling against increasing resistance. This was a form of sub-maximal aerobics. Fourteen women took part in the study but only six traces could be analysed. The mean duration of the exercises was 15 (+/- 2.5) minutes. The mothers' heart rate rose from 84 (+/- 7) beats a minute (bpm) before exercise to 153 (+/- 14) bpm at the last level reached. It took 15.6 (+/- 4) minutes for the maternal heart rate to return to what it was before exercise. The basal fetal heart rate was around 144 (+/- 5) bpm before exercise and rose to 170 (+/- 12) during exercise with no change in the oscillations in the fetal heart rate. After exercise the fetal rate slowed down very slowly and there was a marked diminution in the amplitude of the oscillations (Hammacher's Type 1). They never disappeared. Those few women who were in "false labour" during the test went out of false labour. We have hypothesised that the fetal heart rate rises significantly during the mother's exercise and this action is a mechanical one rather than a humoral or hormonal one. When exercise stops the diminution in oscillations, which is rapid, could be a sign of the fetus becoming drowsy, or it could be due to the intervention of maternal factors.

Adult↗
PubMed1985

All out anaerobic capacity tests on cycle ergometers. A comparative study on men and women.

We have studied the effects of the braking force on the results of an anaerobic capacity test derived from the Wingate test (an all out 45 s exercise on a Monark 864 cycle ergometer against a given force at the fastest velocity from the beginning to the end of the test). Seven men and seven women participated in the study and performed a total of 63 all-out tests against different braking forces. The same subjects performed a force-velocity test on the same cycle ergometer. Since the relationship between force and velocity is approximately linear for peak velocities between 100 and 200 rev X min-1 (Pérès et al. 1981a, b; Nadeau et al. 1983; Vandewalle et al. 1983) we characterized each subject by three parameters: P0 (the intercept of the force-velocity regression line with the force axis), V0 (the intercept of the regression line with the velocity axis) and Wmax (maximal power). The relationship between force and mean power was parabolic for the all-out anaerobic capacity test. In the present study the optimal force (the force giving the maximal value of mean power during an all out test) was higher for the men (approximately 1 N X kg BW-1) than the force proposed by others (0.853 N X kg BW-1 for Dotan and Bar-Or 1983). However, because of the parabolic relationship between force and mean power, the mean power which corresponds to the optimal force was approximately the same in both studies.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗