Effects of stopping exercise training on epinephrine-induced lipolysis in humans

It has been reported that in rats endurance exercise training enhances the sensitivity of adipose tissue to the lipolytic action of catecholamines. The purpose of this study was to determine whether endurance training has a similar effect on the lipolytic response to epinephrine in humans. Four days after cessation of training, a constant infusion of epinephrine resulted in a significantly smaller increase in serum free fatty acids (0.57 ± 0.40 vs. 1.06 ± 0.30 mM; P < 0.01) and blood glycerol (0.07 ± 0.01 vs. 0.12 ± 0.03 mM; P < 0.01) and a greater rise in blood lactate (1.24 ± 0.51 vs. 0.69 ± 0.4 mM; P < 0.01) above preinfusion levels than when the subjects were training. No further change in these reponses occurred after 2 mo on inactivity. Plasma glucose and glucagon responses to epinephrine remained constant throughout the study. Plasma insulin concentrations before and during epinephrine infusion were higher than in the trained state only after 2 mo of inactivity. These findings suggest that epinephrine-induced lipolysis is enhanced in endurance-exercise-trained individuals but that this adaptation is lost very rapidly after cessation of exercise.