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Le système nerveux sympathique et la dépense d'énergie dans l'obésité

Éric Ravussin
ÉR

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Éric Ravussin

Résumé du colloque

The Pima Indians, who have an extraordinarily high prevalence of obesity, exhibit low levels of sympathetic nervous system (SNS) activity as compared to Caucasians. In addition, beta blockade (propranolol) of the SNS, which decreases energy expenditure in Caucasians, does not have the same effect in Pima Indians. Because the effects of the SNS on energy expenditure (metabolic rate and fat oxidation) may be factors predisposing individuals to obesity, an investigation of the determinants of SNS activity was undertaken. We hypothesized that since glucocorticoids inhibit SNS activity, hypercortisolism may underlie the low levels of SNS activity observed in the Pima Indians. We measured indices of the hypothalamic-pituitary-adrenal (HPA) axis and SNS activities in 39 non-diabetic men, 20 Pima Indian and 19 Caucasian matched for body weight and body composition. HPA activity was assessed by measurements of fasting ACTH and cortisol concentrations and 24 hour urinary free cortisol (UFC) excretion. SNS activity was assessed by microneurography (muscle sympathetic nervous system activity, MSNA) and measurements of catecholamine concentrations. Plasma ACTH and cortisol and urinary UFC concentrations were similar in Pima Indians and Caucasians. MSNA was positively correlated with percent body fat and was lower in Pima Indians compared to Caucasians after adjustment for percent fat (24+9 vs. 31+10 bursts/min, p=0.004). However, at each level of plasma ACTH or cortisol concentration, adjusted MSNA was significantly lower in Pima Indians than Caucasians (p=0.04). We conclude that the lower SNS activity in Pima Indians may be the result of higher sensitivity of the SNS to the inhibitory effect of glucocorticoids, i.e., functional hypercortisolism. To further test this hypothesis, we have gathered preliminary data using chemical adrenalectomy (metyrapone) and glucocorticoid replacement which will be discussed.

Contexte

Section :
La régulation du bilan d'énergie
news icon Thème du colloque :
La régulation du bilan d'énergie
host icon Hôte : Université Laval

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Thème du colloque :

La régulation du bilan d'énergie
Le système nerveux sympathique et la dépense d'énergie dans l'obésité
Éric Ravussin