Adrenergic control of lipolysis in women compared with men

This study aimed to determine the specific adrenergic receptor(s) that may mediate these sex differences. Lean women (n = 14) and men (n = 16) were studied on 4 nonconsecutive days during the following treatment infusions: saline (S: control), epinephrine [E: mixed beta-adrenergic (lipolytic) and alpha(2)-adrenergic (antilipolytic) stimulation], epinephrine + phentolamine (E + P: mixed beta-adrenergic stimulation only), and terbutaline (T: selective beta(2)-adrenergic stimulation). Tracer infusions of glycerol, palmitate, and glucose were administered to determine systemic lipolysis, free fatty acid (FFA) release, and glucose turnover, respectively. Following basal measurements, substrate and hormone concentrations were measured in all subjects over 90 min of treatment and tracer infusion. Women had greater increases in glycerol and FFA concentrations with all three hormone infusions compared with men (P < 0.01). Glycerol and palmitate rate of appearance (Ra) and rate of disappearance (Rd) per kilogram body weight were greater with E infusion in women compared with men (P < 0.05), whereas no sex differences were observed with other treatments. Glucose concentration and kinetics were not different between sexes with any infusion. In conclusion, these data support the hypothesis that the greater rate of lipolysis in women with infusion of E was likely due to lesser alpha(2) antilipolytic activation. These findings may help explain why women have greater lipolysis and fat oxidation during exercise, a time when epinephrine concentration is elevated.