OBJECTIVE: To explore sex differences in the regulation of lipolysis during exercise, the lipid-mobilizing mechanisms in the subcutaneous adipose tissue (SCAT) of overweight men and women were studied using microdialysis. RESEARCH METHODS AND PROCEDURES: Subjects matched for age, BMI, and physical fitness performed two 30-minute exercise bouts in a randomized fashion: the first test at 30% and 50% of their individual maximal oxygen uptake (VO2max) and the second test at 30% and 70% of their VO2max. RESULTS: In both groups, an exercise-dependent increment in extracellular glycerol concentration (EGC) was observed. Whatever the intensity, phentolamine (alpha-adrenergic receptor (AR) antagonist) added to a dialysis probe potentiated exercise-induced lipolysis only in men. In a probe containing phentolamine plus propranolol (beta-AR antagonist), no changes in EGC occurred when compared with the control probe when exercise was performed at 30% and 50% VO2max. A significant reduction of EGC (when compared with the control probe) was observed in women at 70% VO2max. At each exercise power, the plasma non-esterified fatty acid and glycerol concentrations were higher in women. Exercise-induced increase in plasma catecholamine levels was lower in women compared with men. Plasma insulin decreased and atrial natriuretic peptide increased similarly in both groups. DISCUSSION: Overweight women mobilize more lipids (assessed by glycerol) than men during exercise. Alpha-sub-2-anti-lipolytic effect was functional in SCAT of men only. The major finding is that during low-to-moderate exercise periods (30% and 50% VO2max), lipid mobilization in SCAT relies less on catecholamine-dependent stimulation of beta-ARs than on an increase in plasma atrial natriuretic peptide concentrations and the decrease in plasma insulin.

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