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M C Thibault

Publications and source records attributed to M C Thibault.

30 records · Page 2Linked to original sources
PubMed1986

Repeatability of fibre type and enzyme activity measurements in human skeletal muscle.

In order to assess the variability in repeated determination of human muscle fibre type distribution, fibre area and enzyme activity measurements, two biopsies were taken within 10 days in the same vastus lateralis for 12 females and 13 males, and in the right and in the left muscles for 25 other subjects (13 females and 12 males). Within muscle, intraclass reliability coefficients were 0.88, 0.82 and 0.56 for type I, IIa and IIb per cent fibres, respectively, and ranged from 0.74 to 0.82 for fibre areas and from 0.71 to 0.90 for enzyme markers of different metabolic pathways. Correlations between right and left muscle measurements were also high for fibre areas (from 0.85 to 0.91) and enzyme activities (from 0.71 to 0.87), except for phosphofructokinase (r = 0.63). In contrast, the right and left thigh muscle correlation reached 0.67, 0.40 and 0.64 for type I, IIa and IIb fibre distribution, respectively. Thus, the variation in muscle sampling and technical procedures reached about 15% of the total variation (i.e. total differences between subjects) for the proportion of fibre type I and IIa and about 20-25% for fibre areas and enzyme activities. On the other hand, the technical error for the proportion of fibre type I and IIa is about 6-7%. This implies that differences brought about by any experimental treatment on these skeletal muscle characteristics in human studies have to be of a relatively large magnitude before being detectable. On the other hand, fibre areas and enzyme activities measured in single needle biopsy sample, from one of the vastus lateralis muscles, are quite representative of the other vastus lateralis. Similarity in fibre type proportion between right and left vastus lateralis cannot be postulated, however, without investigating both muscles.

Adult↗
PubMed1986

Genetic effects in human skeletal muscle fiber type distribution and enzyme activities.

The purpose of the study was to estimate the genetic effect for skeletal muscle characteristics using pairs of nontwin brothers (n = 32), dizygotic (DZ) twins (n = 26), and monozygotic (MZ) twins (n = 35). They were submitted to a needle biopsy of the vastus lateralis for the determination of fiber type distribution (I, IIa, IIb) and the following enzymes were assayed for maximal activity: creatine kinase, hexokinase, phosphofructokinase (PFK), lactate dehydrogenase, malate dehydrogenase, 3-hydroxyacyl CoA dehydrogenase, and oxoglutarate dehydrogenase (OGDH). For the percentage of type I fibers, intraclass correlations were 0.33 (p less than 0.05), 0.52 (p less than 0.01), and 0.55 (p less than 0.01) in brothers and DZ and MZ twins, respectively. MZ twins exhibited significant within-pair resemblance for all enzyme activities (0.30 less than or equal to r less than or equal to 0.68). In spite of these correlations, genetic analyses performed with the twin data alone indicated that there was no significant genetic effect for muscle fiber type I, IIa, and IIb distribution and fiber areas. Although there were significant correlations in MZ twins for all muscle enzyme activities, the often nonsignificant intraclass coefficients found in brothers and DZ twins suggest that variations in enzyme activities are highly related to common environmental conditions and nongenetic factors. However, genetic factors appear to be involved in the variation of regulatory enzymes of the glycolytic (PFK) and citric acid cycle (OGDH) pathways and in the variation of the oxidative to glycolytic activity ratio (PFK/OGDH ratio). Data show that these genetic effects reach only about 25-50% of the total phenotypic variation when data are adjusted for age and sex differences.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1986

Inheritance of human muscle enzyme adaptation to isokinetic strength training.

Five monozygotic twin pairs were submitted to a 10-week isokinetic strength training program and biochemical characteristics measured before and after training to determine the role of heredity in skeletal muscle adaptation, while 5 unrelated sedentary subjects served as control group. Experimental subjects performed twice 3 series of 5 bilateral reciprocal alternating knee flexions and extensions at a velocity of 90 degrees/s 5 times per week. Before and after the training period, for each subject, the peak muscular torque output was measured at the same velocity and the vastus lateralis muscle was biopsied for biochemical determinations. No significant change was observed in the control group. Training increased peak muscular torque output by 24%. The activities of hexokinase, malate dehydrogenase and 3-hydroxyacyl CoA dehydrogenase also increased significantly by 28, 26 and 38%, respectively. Interindividual variations in the response of these variables to training were noted but these were shown to be independent of the genotype. No overall effect of training was observed for oxoglutarate dehydrogenase activity (OGDH). However, changes were seen in individual pairs of twins and these were in opposite directions in some pairs compared to others, thus explaining the absence of a general training effect. Significant intrapair resemblance in the training response was present for OGDH (r = 0.76), indicating that the sensitivity to isokinetic strength training for OGDH was highly variable, not random and probably genetically determined.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1985

Effect of endurance training and chronic isoproterenol treatment on skeletal muscle sensitivity to norepinephrine.

The purpose of this study was to determine the influence of metabolic stresses, such as endurance training and chronic isoproterenol treatment, on skeletal muscle sensitivity to norepinephrine. Using an isolated perfused rat hindlimb preparation, dose-response curves for skeletal muscle oxygen consumption (VO2) and vascular resistance were obtained with control, endurance trained, and isoproterenol treated rats. No significant difference was found between control and experimental groups for non-stimulated VO2. In response to NE infusion, trained rats showed a significantly greater increase in VO2 compared to control rats while the response of the isoproterenol treated rats was of the same magnitude as the one for their respective control rats. At the highest dose of NE infused, the vasopressor response was significantly lower in trained rats compared to control rats. At none of the doses was there a significant difference in the vasopressor response between control and isoproterenol treated rats. These results suggest that repeated exposures to high levels of catecholamines, as produced during endurance training, leads to an increased sensitivity of skeletal muscle to the effect of norepinephrine.

Animals↗
PubMed1985

Human skeletal muscle fiber type alteration with high-intensity intermittent training.

The response of muscle fiber type proportions and fiber areas to 15 weeks of strenuous high-intensity intermittent training was investigated in twenty-four carefully ascertained sedentary (14 women and 10 men) and 10 control (4 women and 6 men) subjects. The supervised training program consisted mainly of series of supramaximal exercise lasting 15 s to 90 s on a cycle ergometer. Proportions of muscle fiber type and areas of the fibers were determined from a biopsy of the vastus lateralis before and after the training program. No significant change was observed for any of the histochemical characteristics in the control group. Training significantly increased the proportion of type I and decreased type IIb fibers, the proportion of type IIa remained unchanged. Areas of type I and IIb fibers increased significantly with training. These results suggest that high-intensity intermittent training in humans may alter the proportion of type I and the area of type I and IIb fibers and in consequence that fiber type composition in human vastus lateralis muscle is not determined solely by genetic factors.

Adult↗
PubMed1985

Skeletal muscle histochemical and biochemical characteristics in sedentary male and female subjects.

The purpose of this study was to assess the relationship between muscle fiber type distribution and enzymatic characteristics in sedentary male and female subjects. Muscle biopsy samples from the vastus lateralis muscle of 38 females and 37 males were analyzed to determine the fiber type composition (I, IIa, and IIb), the fiber size, and maximal activities of enzyme markers of energy metabolic pathways. Significant correlations were found (p less than 0.05) between percent fiber type I area and hexokinase (r = -0.39), phosphofructokinase (r = -0.39), lactate dehydrogenase (r = -0.41), and oxoglutarate dehydrogenase (r = 0.33) activities, whereas such correlations with total phosphorylase (r = -0.02), malate dehydrogenase (r = 0.12), and 3-hydroxyacyl CoA dehydrogenase (r = 0.12) activities were not significant. The results of the present study also suggest the presence of a significant but low covariation of less than 30% between the fiber type distribution and muscle enzyme activities. They confirm the presence of an important metabolic heterogeneity independent of the muscle fiber type distribution in sedentary male and female subjects. Moreover, these results indicate that sedentary males exhibit a lower mean value of percent fiber type I and higher glycolytic enzyme activities than sedentary females.

Adult↗
PubMed1982

Effects of exercise and time elapsed after exercise on VO2, VCO2 and R responses to norepinephrine in rats.

The effects of norepinephrine (NE) injection (300 microgram . kg-1 of body weight) on oxygen consumption (VO2), carbon dioxide production (VCO2) and respiratory exchange ratio (R) were investigated in female rats after 1 h of running on a treadmill (21.5 m . min-1) at 10% inclination. Six groups of animals were injected respectively at various times after the exercise (1, 3, 6, 9, 21, and 47 h), and were compared to six non-exercised groups injected at corresponding times. VO2 and VCO2 were monitored continuously during the 20 min preceding injection and for the 60 min following it. The increases in VO2 and VCO2, and the decrease in R were of similar magnitude in both exercised and non-exercised rats (about 30% and 20% for VO2 and VCO2, respectively, and -12% for R). Peak VO2 and R values attained after NE injection varied however with time of injection, specially in exercised animals 1 and 9 h after the run. Exercise significantly delayed time of response to NE for VO2 and VCO2 particularly 1 and 9 h after the running bout. It is concluded that time of day, exercise, and time elapsed after exercise are important factors to consider when studying metabolic responses to catecholamines. Furthermore, it is suggested that such experimental controls might be meaningful in human studies as well.

Animals↗
PubMed1981

Norepinephrine mobilization of free fatty acids in endurance trained rats.

Wistar rats were trained to run, a male group on 6 days a week for 4 months at 28 m x min-1, and a female group on 5 days a week for 5-6 months at 31 m x min-1. Male rats were given continuous infusion of [1-14C] palmitate-albumin tracer via a jugular catheter at a constant infusion rate of 80 nCI x min-1. The effect of concurrent norepinephrine (NE) infusion on free fatty acid (FFA) mobilization was then studied in this group. NE increased plasma FFA levels similarly in both control and endurance trained male groups. Turnover of FFA, however, increased in response to NE relatively less in the trained group. Furthermore, NE caused the metabolic clearance rate of FFA (MCR) to decrease in control animals but not in runners. Colonic temperature was slightly increased by NE infusion in the control group only. Female rats were given a bolus injection of 5 microCi of [1-14C] palmitate-rat serum through a venous cannula. The disappearance of radioactivity in the circulation was measured. MCR values were higher in the trained group (p = 0.01). The effect of NE infusion on FFA levels was also studied in female animals. NE caused levels to increase in both control and trained rats. FFA concentrations were however more elevated in the control than in the trained group, before and during NE infusion. The relative increase tended to be less extensive in the trained group (p = 0.06). It is concluded that long term endurance training diminishes calorigenic and fat mobilizing actions of NE in the rat in vivo.

Animals↗
PubMed1981

Trophic effect of a sciatic nerve extract on fast and slow myosin heavy chain synthesis.

Myosin heavy chain (MHC) synthesis in cultures from chick pectoralis muscle cells was determined by [35S]methionine incorporation. Two types of MHC, migrating as 200,000-dalton components on sodium dodecyl sulfate polyacrylamide gels, were distinguished with antibodies against adult fast and slow MHC. Their synthesis was revealed by autoradiography. The effect of a sciatic nerve extract on the synthesis of the two types of MHC was also determined. Control experiments show that fast MHC is primarily synthesized in 48-h cultures. At a later stage of development (5- to 7-day cultures), slow MHC is also produced. The nerve extract promotes muscle cell differentiation and stimulates the synthesis of the slow type of MHC at an earlier stage of development (i.e., at 48 h as compared with 5-7 day in controlled cultures). It is concluded therefore that presumptive fast muscle cells in culture synthesize initially fast MHC and later both types of MHC (slow and fast). These results also suggest that the sciatic nerve extract is capable either of activating the transcription of the structural gene for slow MHC or of activating the translation of preexisting messenger RNA coding for this protein.

Animals↗