Lipolytic response of adipocytes to epinephrine in sedentary and exercise-trained subjects: sex-related differences

Summary

Adipose tissue lipolytic activity is increased in endurance-trained subjects, but little is known about the mechanisms of this increase. To understand more fully the mechanisms involved and to discover whether sex-related differences exist, biopsies of fat were performed in the periumbilical region of 20 sedentary subjects (10 women (W) and 10 men (M)) and 20 trained subjects (10 W, 10 M); the in vitro response to epinephrine of the collagenase-isolated fat cells was studied. Glycerol release, chosen as an adipocyte lipolysis indicator, was measured by bioluminescence. Dose-response curves with epinephrine (α₂ and β agonist), with isoproterenol (β agonist) and epinephrine + propranolol and adenosine deaminase, were studied. Epinephrine-induced lipolysis was enhanced in trained subjects and this was due to an increased efficiency of the β-adrenergic pathway. However, differences were found between the two sexes. In trained men, the lipolysis increase resulted from the enhancement of the β-adrenergic pathway efficiency without any significant decrease in the α₂-adrenergic pathway efficiency. In trained women, the lipolysis increase was not only due to the enhancement of the β-adrenergic pathway efficiency (which was greater than in trained men), but also to a significant decrease in the α₂-adrenergic pathway efficiency. Despite the decrease, the α₂-adrenergic pathway remained more efficient in trained women than in trained men, as was the case in sedentary subjects. It is concluded that endurance training led to better lipid mobilization and that this effect seemed greater in women than in men.