Sex Differences in Lipolysis-Regulating Mechanisms in Overweight Subjects: Effect of Exercise Intensity

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 [α-adrenergic receptor (AR) antagonist] added to a dialysis probe potentiated exercise-induced lipolysis only in men. In a probe containing phentolamine plus propranolol (β-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. α2-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 β-ARs than on an increase in plasma atrial natriuretic peptide concentrations and the decrease in plasma insulin.