Greater systemic lipolysis in women compared with men during moderate-dose infusion of epinephrine and/or norepinephrine

Abstract

Women have lower circulating catecholamine levels during metabolic perturbations, such as exercise or hypoglycemia, but similar rates of systemic lipolysis. This suggests women may be more sensitive to the lipolytic action of catecholamines, while maintaining similar glucoregulatory effects. The aim of the present study, therefore, was to determine whether women have higher rates of systemic lipolysis compared with men in response to matched peripheral infusion of catecholamines, but similar rates of glucose turnover. Healthy, nonobese women (n = 11) and men (n = 10) were recruited and studied on 3 separate days with the following infusions: epinephrine (Epi), norepinephrine (NE), or the two combined. Tracer infusions of glycerol and glucose were used to determine systemic lipolysis and glucose turnover, respectively. Following basal measurements of substrate kinetics, the catecholamine infusion commenced, and measures of substrate kinetics continued for 60 min. Catecholamine concentrations were similarly elevated in women and men during each infusion: Epi, 182-197 pg/ml and NE, 417-507 pg/ml. There was a significant sex difference in glycerol rate of appearance and rate of disappearance with the catecholamine infusions (P < 0.0001), mainly due to a significantly greater glycerol turnover during the first 30 min of each infusion: glycerol rate of appearance during Epi was only 268 +/- 18 vs. 206 +/- 21 micromol/min in women and men, respectively; during NE, only 173 +/- 13 vs. 153 +/- 17 micromol/min, and during Epi+NE, 303 +/- 24 vs. 257 +/- 21 micromol/min. No sex differences were observed in glucose kinetics under any condition. In conclusion, these data suggest that women are more sensitive to the lipolytic action of catecholamines, but have no difference in their glucoregulatory response. Thus the lower catcholamine levels observed in women vs. men during exercise and other metabolic perturbations may allow women to maintain a similar or greater level of lipid mobilization while minimizing changes in glucose turnover.

Fig. 1.

Glycerol tracer enrichment, expressed as mole percent excess (MPE%) is shown at rest (90–120 min) and during epinephrine (Epi; A), norepinephrine (NE; B), and Epi + NE (C) infusion (130–180 min). Values are means ± SE.

Fig. 2.

Glycerol concentration is shown at rest (90–120 min) and during Epi (A), NE (B), and Epi + NE (C) infusion (130–180 min). Significant time × infusion interaction (P < 0.0001) and time × sex interaction (P < 0.0001). Post hoc comparisons revealed a significant difference between Epi + NE vs. NE (P < 0.0001). Values are means ± SE.

Fig. 3.

Glycerol rate of appearance (R_a) is shown at rest (100–120 min) and during Epi (A), NE (B), and Epi + NE (C) infusion (130–180 min). Significant time × infusion interaction (P < 0.0001) and time × sex interaction (P < 0.0001). Post hoc comparisons revealed a significant difference between Epi vs. NE (P = 0.02) and Epi + NE vs. NE (P < 0.0001). Values are means ± SE.

Fig. 4.

Nonesterified fatty acid concentration is shown at rest (90–120 min) and during Epi (A), NE (B), and Epi + NE (C) infusion (130–180 min). Significant time × infusion interaction (P < 0.001) and time × sex interaction (P < 0.002). Post hoc comparisons revealed a significant difference between Epi vs. NE (P = 0.045) and Epi + NE vs. NE (P = 0.003). Values are means ± SE. FFA, free fatty acid.