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Biomedical subjects

J Mercier

Publications and source records attributed to J Mercier.

At least 73 records · Page 4Linked to original sources
PubMed2000

The effects of exercise training intensification on glucose disposal in elite cyclists.

To assess the effect of training on glucose disposal, we performed a longitudinal study of 11 elite cyclists before and after 4 months of intensive training compared to 11 sedentary subjects. Insulin sensitivity (SI) and glucose effectiveness (Sg) were measured using Bergman's minimal model. Sg includes basal insulin effectiveness (BIE) and a parameter termed glucose effectiveness at zero insulin (GEZI). After overnight fasting glucose was administered intravenously (0.5 g x kg(-1), 30% solution given over 3 min), and insulin (0.02 U x kg(-1), 1 -2U) was injected immediately after 19 min. Sg, SI and BIE, were significantly higher in elite cyclists both before and after training than in sedentary subjects (P < 0.01). However, the non-insulin-dependent component of Sg (GEZI) was higher only after the intensive training in the cyclists (3.31 +/- 0.67% x min(-1)) than in sedentary subjects (1.7 +/- 0.2% x min(-1), P < 0.02). We conclude that insulin sensitivity (SI) and glucose effectiveness (Sg) are higher in elite cyclists than in sedentary subjects and that these high and almost optimal values are not further improved by additional training. However, the improvement in GEZI, as reflected by the difference between post-training GEZI and sedentary control values, raises the possibility of an increase of the non-insulin-mediated mobilization of glucose transporters.

Adult↗
PubMed2000

Lactate transport in rat sarcolemmal vesicles after a single bout of submaximal exercise.

We investigated the effects of a single bout of non-exhaustive exercise (25 m x min(-1), 10% grade, for 30 min) on the initial rates of lactate uptake in rat skeletal muscle sarcolemmal vesicles and the monocarboxylate transporter 1 (MCT1) content in isolated hindlimb muscles in relation to the exercise-induced oxidative stress. The exercise led to a decrease in red gastrocnemius and red vastus lateralis muscle glycogen content by 74% and 83%, respectively, and an increase in blood lactate concentration from 1.67 +/- 0.15 to 3.44 +/- 0.47 mM (p < 0.05). Initial rates of lactate uptake were measured in zero-trans conditions, at pH 7.4, for 1, 10, 30 and 100 mM external lactate concentrations. Lactate transport capacity was significantly decreased at 1 mM in the exercised group (p < 0.05), while a non-significant trend towards an increase was observed at 10, 30 and 100 mM. We failed to obtain any change in soleus, red tibialis anterior and white gastrocnemius muscle MCT1 content (p>0.05), and no evidence of exercise-induced oxidative stress in terms of muscle malondialdehyde content and glutathione peroxidase and superoxide dismutase activities was observed after the 30 min exercise bout. These results indicate that a single bout of submaximal exercise, which did not induce an increase in muscle MCT1 content and apparent oxidative stress, decreased lactate transport capacity at low physiological concentration. Although the changes are small and independent of a MCT1-facilitated lactate transport regulation, we suggest that another MCT isoform with different kinetic properties from MCT1 could be present in the sarcolemma and responsible for lactate exchange alterations.

Animals↗
PubMed2000

Effects of aging on cardiorespiratory responses to brief and intense intermittent exercise in endurance-trained athletes.

The aim of this study was to investigate the effects of aging on athletes' cardiorespiratory responses to a brief intense intermittent effort, using the force-velocity test as an exercise model. Twelve young athletes (24.8 +/- 1.3 years) and twelve master athletes (65.1 +/- 1.2 years) with similar heights, body masses, and endurance training schedules participated in this study. They performed both a maximal graded exercise and the force-velocity tests. The force-velocity test consisted of the repetition of 6-second sprints against increasing braking forces with 5-minute recovery periods. None of the subjects presented abnormal electrocardiogram responses to the tests. During the force-velocity test, the heart rate magnitudes of response in all subjects were correlated to the corresponding sprint power output (p < .001), with higher values for the young athletes (p < .001). Both groups had similar systolic blood pressure peaks of response during the force-velocity test. Both groups had similar preexercise and end-of-recovery oxygen consumption (VO2), but the young athletes had higher peaks of response (p < .001). The VO2 magnitudes of response increased during the test (p < .01) in all subjects, with higher values for the young athletes (p < .001). There was a positive correlation between the VO2 magnitude of response and (1) the corresponding sprint power output (R = .58,p < .001) and (2) the corresponding number of sprint repetitions (R = .29, p < .02). The young athletes had higher end-of-recovery and peak carbon dioxide production (VCO2) responses than the master athletes (p < .001). Pulmonary ventilation (V(E)) peaks of response to the sprints were higher in the young athletes (p < .001). There was a positive relation between the V(E) and VCO2 peaks of response (R = 84,p < .001). In both groups the peak heart rate, VO2, VCO2, and V(E) values attained during the force-velocity test represented similar percentages of the maximal values reached at exhaustion of maximal graded exercise. These results showed that aging does not alter the percentage of the cardiorespiratory response to a brief intense intermittent exercise such as the force-velocity test. Moreover, the arterial blood pressure response is not significantly altered, whereas the vasodilatatory response is.

Adolescent↗
PubMed2000

Role of leaf surface sugars in colonization of plants by bacterial epiphytes.

The relationship between nutrients leached onto the leaf surface and the colonization of plants by bacteria was studied by measuring both the abundance of simple sugars and the growth of Pseudomonas fluorescens on individual bean leaves. Data obtained in this study indicate that the population size of epiphytic bacteria on plants under environmentally favorable conditions is limited by the abundance of carbon sources on the leaf surface. Sugars were depleted during the course of bacterial colonization of the leaf surface. However, about 20% of readily utilizable sugar, such as glucose, present initially remained on fully colonized leaves. The amounts of sugars on a population of apparently identical individual bean leaves before and after microbial colonization exhibited a similar right-hand-skewed distribution and varied by about 25-fold from leaf to leaf. Total bacterial population sizes on inoculated leaves under conditions favorable for bacterial growth also varied by about 29-fold and exhibited a right-hand-skewed distribution. The amounts of sugars on leaves of different plant species were directly correlated with the maximum bacterial population sizes that could be attained on those species. The capacity of bacteria to deplete leaf surface sugars varied greatly among plant species. Plants capable of supporting high bacterial population sizes were proportionally more depleted of leaf surface nutrients than plants with low epiphytic populations. Even in species with a high epiphytic bacterial population, a substantial amount of sugar remained after bacterial colonization. It is hypothesized that residual sugars on colonized leaves may not be physically accessible to the bacteria due to limitations in wettability and/or diffusion of nutrients across the leaf surface.

Carbohydrates↗
PubMed2000

The double-stranded RNA-binding protein Staufen is incorporated in human immunodeficiency virus type 1: evidence for a role in genomic RNA encapsidation.

Human Staufen (hStau), a double-stranded RNA (dsRNA)-binding protein that is involved in mRNA transport, is incorporated in human immunodeficiency virus type 1 (HIV-1) and in other retroviruses, including HIV-2 and Moloney murine leukemia virus. Sucrose and Optiprep gradient analyses reveal cosedimentation of hStau with purified HIV-1, while subtilisin assays demonstrate that it is internalized. hStau incorporation in HIV-1 is selective, is dependent on an intact functional dsRNA-binding domain, and quantitatively correlates with levels of encapsidated HIV-1 genomic RNA. By coimmunoprecipitation and reverse transcription-PCR analyses, we demonstrate that hStau is associated with HIV-1 genomic RNA in HIV-1-expressing cells and purified virus. Overexpression of hStau enhances virion incorporation levels, and a corresponding, threefold increase in HIV-1 genomic RNA encapsidation levels. This coordinated increase in hStau and genomic RNA packaging had a significant negative effect on viral infectivity. This study is the first to describe hStau within HIV-1 particles and provides evidence that hStau binds HIV-1 genomic RNA, indicating that it may be implicated in retroviral genome selection and packaging into assembling virions.

Binding Sites↗
PubMed2000

Training does not protect against exhaustive exercise-induced lactate transport capacity alterations.

The effects of endurance training on lactate transport capacity remain controversial. This study examined whether endurance training 1) alters lactate transport capacity, 2) can protect against exhaustive exercise-induced lactate transport alteration, and 3) can modify heart and oxidative muscle monocarboxylate transporter 1 (MCT1) content. Forty male Wistar rats were divided into control (C), trained (T), exhaustively exercised (E), and trained and exercised (TE) groups. Rats in the T and TE groups ran on a treadmill (1 h/day, 5 days/wk at 25 m/min, 10% incline) for 5 wk; C and E were familiarized with the exercise task for 5 min/day. Before being killed, E and TE rats underwent exhaustive exercise (25 m/min, 10% grade), which lasted 80 and 204 min, respectively (P < 0.05). Although lactate transport measurements (zero-trans) did not differ between groups C and T, both E and TE groups presented an apparent loss of protein saturation properties. In the trained groups, MCT1 content increased in soleus (+28% for T and +26% for TE; P < 0.05) and heart muscle (+36% for T and +33% for TE; P < 0.05). Moreover, despite the metabolic adaptations typically observed after endurance training, we also noted increased lipid peroxidation byproducts after exhaustive exercise. We concluded that 1) endurance training does not alter lactate transport capacity, 2) exhaustive exercise-induced lactate transport alteration is not prevented by training despite increased MCT1 content, and 3) exercise-induced oxidative stress may enhance the passive diffusion responsible for the apparent loss of saturation properties, possibly masking lactate transport regulation.

Animals↗
PubMed2000

Relationships between blood viscosity and insulin-like growth factor I status in athletes.

Exercise training is known (1) to enhance the function of the GH-IGF-I system, which has profound effects on body fluid status; (2) to increase blood fluidity. Thus, we investigated during an exercise-test in 39 male elite sportsmen (age 23.7+/-0.72 years; body mass index 23.7+/-0.28 kg/m2) the possible relationships between GH and IGF-I status and the rheological properties of blood. Two correlations indicate a relationship between body hydration and fitness: isometric handgrip strength is correlated with the percentage of extracellular water in total body water (r = 0.432, p = 0.02) and the aerobic working capacity W170 is negatively correlated with hematocrit (r = -0.341, p = 0.039). Water loss during exercise appears to be inversely related to fitness as evaluated by W170 (r = -0.529, p = 0.05), and is positively correlated with the score of signs of overtraining (r = 0.725, p = 0.003) and with the red blood cell aggregation index (r = 0.584, p = 0.036). Finally, while the GH peak value is correlated with the extracellular water volume (r = 0.393, p = 0.02), IGF-I is correlated with blood viscosity (r = 0.546, p = 0.0003), suggesting that when IGF-I values are within the upper quintile (>340 ng/ml) IGF-I may unfavourably affect blood rheology. Among factors of blood viscosity, IGF-I exhibits a borderline correlation (p = 0.05) with "Tk" and the ratio IGF1/IGFBP3 which reflects free circulating IGF-I is correlated with red cell aggregability measured with the Myrenne "M" (r = 0.485, p = 0.014) and S60 (r = 0.396, p = 0.494). These findings confirm the importance of hydration and dehydration as determinants of both blood rheology and exercise performance. Moreover, they suggest that values of IGF-I within the upper quintile are associated with an impairment of blood fluidity, possibly due to a direct effect of IGF-I on red cell deformability and aggregability.

Adult↗
PubMed2000

The paradox of hematocrit in exercise physiology: which is the "normal" range from an hemorheologist's viewpoint?

The paradox of hematocrit in exercise physiology is that artificially increasing it by autotransfusion or erythropoietin doping improves VO2 max and performance, while in normal conditions there is a strong negative correlation between hematocrit and fitness, due to a training-induced "autohemodilution". We aimed at investigating: (a) which is the physiological range of hematocrit in highly trained professional footballers; (b) what are the characteristics of athletes with high vs low hematocrit? We determined in 77 healthy male footballers the physiological range (mean +/- sd) of hematocrit: 42.3+/-2.74, (range -2sigma/+2sigma = 36.8-47.8%) thus defining boundaries of quintiles of distribution for this parameter: 40, 41.6, 42.9, 44.6. In another sample of 42 male footballers we compared three groups: lowest quintile (n = 8), highest quintile (n = 5) and the three middle quintiles considered together (n = 29). Athletes in the lowest quintile compared to those in the four other quintiles had a lower value of blood viscosity (-8%, p < 0.01) but this difference disappeared after correction for hematocrit. These subjects with low hematocrit had also higher values of the following parameters: aerobic working capacity (p < 0.01); isometric adductor strength (p = 0.02); crossover point of carbohydrate oxidation (70% carbohydrates/30% lipids) (p < 0.05); insulin like growth factor binding protein 1 (p < 0.0001). Athletes in the highest quintile had higher red cell aggregability (Myrenne index "M1" 8.45+/-0.38 vs 6.82+/-0.62, p < 0.04) and a higher disaggregability threshold gammaD (72.6+/-22.63 vs 44.49+/-1.37, p < 0.01) and a lower percentage of water in fat-free mass (p < 0.02). On the whole sample hematocrit was negatively correlated with aerobic working capacity (W170 r = -0.329, p = 0.007; Wmax (% of expected value) r = -0.552, p = 0.008; VO2 max (% of expected value) r = -0.543, p = 0.009) and with ferritin (r = -0.33, p = 0.031), and positively correlated with the overtraining score (r = 0.352, p = 0.019) which was in turn negatively correlated with ferritin r = -0.312, p = 0.02). Besides, hematocrit behaves as a major determinant of blood viscosity (correlation with blood viscosity r = 0.997, p < 10(-7)) and erythrocyte disaggregability gammaD (r = 0.384, p = 0.03), but the hematocrit/viscosity ratio (h/eta index of O2 delivery) remains maintained almost constant over the range of values studied. These results show that (a) physiological values of hematocrit in these athletes are comprised between 36 and 48%; (b) "low" hematocrit (<40%) was associated with a higher aerobic capacity; (c) subjects with the higher hematocrits (>44.6%) were frequently overtrained and/or iron-deficient, and their blood viscosity (and red cell disaggregability) tended to be increased.

Adaptation, Physiological↗
PubMed2000

Postprandial reactive hypoglycemia.

Postprandial reactive hypoglycemia (PRH) can be diagnosed if sympathetic and neuroglucopenic symptoms develop concurrently with low blood sugar (<3.3 mmol). Neither the oral glucose tolerance test (OGTT) nor mixed meals are suitable for this diagnosis, due to respectively false positive and false negative results. They should be replaced by ambulatory glycemic control or, as recently proposed, an hyperglucidic breakfast test. PRH patients often suffer from an associated adrenergic hormone postprandial syndrome, with potential pathologic consequences such as cardiac arrhythmia. PRH could result from (a) an exaggerated insulin response, either related to insulin resistance or to increased glucagon-like-peptide 1; (b) renal glycosuria; (c) defects in glucagon response; (d) high insulin sensitivity, probably the most frequent cause (50-70%), which is not adequately compensated by hypoinsulinemia and thus cannot be measured by indices of insulin sensitivity such as the homeostatic model assessment. Such situations are frequent in very lean people, or after massive weight reduction, or in women with moderate lower body overweight. PRH is influenced by patient's alimentary habits (high carbohydrate-low fat diet, alcohol intake). Thus, diet remains the main treatment, although alpha-glucosidase inhibitors and some other drugs may be helpful.

Blood Glucose↗
PubMed2000

[Hemorheological aspects of leuko-platelet activation in atheromatous diseases: clinical applications].

Atherosclerosis (and its evolution towards thrombotic accidents) is now considered to be an inflammatory disease in which the interaction among endothelium, leukocytes and platelets plays a determining role. However, large scale epidemiological studies only indirectly reveal the leukocyte activation through somewhat simplistic markers, such as elastase or leukocyte counts. Interestingly, these markers seem to be independent predictors of ischemia distal to the atheromatous lesion. This leukocyte activation is usually associated with more classical hemorheological disturbances affecting blood viscosity and fibrinogen which, on multivariate analysis, also appear to be determinants of atheromatous lesions and their ischemic and thrombotic consequences, statistically independent of the "classical risk factors". Leukocyte activation probably plays an important role in these hemorheological disturbances, because it is associated with the production of leukocyte secretory products (proteolytic enzymes, free radicals, cytokines) which can alter the red cells and make them more aggregable and more rigid, and can increase the production of fibrinogen. These interactions remain incompletely understood, as illustrated by the still unclear role of NO which, depending on the experimental conditions, can have antiatherogenic or proatherogenic effects. The production by the leukocyte of substances leading to hyperviscosity is amplified by hypoxia, while the improvement in claudication distance resulting from walking exercise is associated with a joint fall of the "classical" factors of viscosity and of leukocyte activation markers. All this suggests that leukocyte activation and hyperviscosity are closely interdependent phenomena in the course of atheromatous disease and that, despite the complexity of these interactions, relatively simple and reasonably priced biological markers of this process will become available to the clinician.

Arterial Occlusive Diseases↗
PubMed1999

Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS): high-resolution physical and transcript map of the candidate region in chromosome region 13q11.

Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS or SACS) is a neurodegenerative disease frequent in northeastern Québec. In a previous study, we localized the disease gene to chromosome region 13q11 by identifying excess sharing of a marker allele in patients followed by linkage analysis and haplotyping. To create a detailed physical map of this region, we screened CEPH mega-YACs with 41 chromosome 13 sequence-tagged-sites (STSs) known to map to 13q11-q12. The YAC contig, composed of 27 clones, extends on the genetic map from D13S175 to D13S221, an estimated distance of at least 19.3 cM. A high-resolution BAC and PAC map that includes the ARSACS critical region flanked by D13S1275 and D13S292 was constructed. These YAC and BAC/PAC maps allowed the accurate placement of 29 genes and ESTs previously mapped to the proximal region of chromosome 13q. We confirmed the position of two candidate genes within the critical region and mapped the other 27 genes and ESTs to nearby intervals. Six BAC/PAC clones form a contig between D13S232 and D13S787 for sequencing within the ARSACS critical region.

Bacteriophage P1↗
PubMed1999

Antioxidants and mitochondrial respiration in lung, diaphragm, and locomotor muscles: effect of exercise.

Previous studies have shown that exhaustive exercise may increase reactive oxygen species (ROS) generation in oxidative muscles that may in turn impair mitochondrial respiration. Locomotor muscles have been extensively examined, but there is few report about diaphragm or lung. The later is a privileged site for oxygen transit. To compare the antioxidant defense system and mitochondrial function in lung, diaphragm and locomotor muscles after exercise, 24 young adult male rats were randomly assigned to a control (C) or exercise (E) group. E group rats performed an exhaustive running test on a motorized treadmill at 80-85% VO2max Mean exercise duration was 66+/-2.7 min. Lung, costal diaphragm, mixed gastrocnemius, and oxidative muscles (red gastrocnemius and soleus: RG/SOL homogenate) were sampled. Mitochondrial respiration was assessed in tissue homogenates by respiratory control index (RCI: rate of uncoupled respiration/rate of basal respiration) measurement. Lipid peroxidation was evaluated by malondialdehyde concentration (MDA) and we determined the activity of two antioxidant enzymes: superoxide dismutase (SOD) and glutathione peroxidase (GPX). We found elevated basal (C group data) SOD and GPX activities in both lung and diaphragm compared to locomotor muscles (p<.001). Exercise led to a rise in GPX activity in red locomotor muscles homogenate (GR/SOL; C = 10.3+/-0.29 and E = 14.4+/-1.51 micromol x min(-1) x gww(-1); p<.05), whereas there was no significant change in lung and diaphragm. MDA concentration and mitochondrial RCI values were not significantly changed after exercise. We conclude that lung and diaphragm had higher antioxidant protection than locomotor muscles. The exercise test did not lead to significant oxidative stress or alteration in mitochondrial respiration, suggesting that antioxidant function was adequate in both lung and diaphragm in the experimental condition.

Animals↗
PubMed1999

Serum leptin is associated with the perception of palatability during a standardized high-carbohydrate breakfast test.

Leptin is an adipocyte-derived signalling molecule which plays a key role in the regulation of body weight and energy expenditure. Since its involvement in human eating behaviour is still poorly understood, we investigated whether the perception of palatability of food was related to fasting serum leptin levels. Twenty-six non-diabetic subjects, six men and twenty women of widely ranging age and body mass index, performed a standardized high-carbohydrate breakfast test. Palatability was evaluated with a visual analogue scale, body composition by bioelectrical impedance, serum leptin and plasma insulin by radioimmunoassay. Palatability was correlated to fasting serum leptin levels independently of body mass index, body fat mass and percentage of body fat (P<0.01). No significant relation was observed with peaks of insulinaemia, integrated concentrations of insulin or insulin resistance indices. A stepwise regression analysis indicated that serum leptin gave the strongest predictive association with palatability. These results suggest that the leptin system may be involved in the regulation of human eating behaviour in relation to the perception of palatability of food.

Adult↗