Lipolytic response of fat cells to catecholamines in sedentary and exercise-trained women

It has been shown that adipose tissue lipolytic activity is increased in endurance-trained subjects. In women, adipose tissue is extensive and it was thought interesting to confirm that endurance training increases the capacity of female adipose tissue to mobilize lipids, and moreover to more fully understand the mechanisms involved. So, biopsies of fat were obtained from the periumbilical region of 13 trained female runners (T) and 17 sedentary women (S) and the in vitro response to catecholamines of the collagenase-isolated fat cells was studied. Glycerol release, chosen as adipocyte lipolysis indicator, was measured by bioluminescence for various epinephrine and norepinephrine concentrations. In both groups, these substances provoked an increase in lipolysis, but the response was significantly higher in T. In both groups, isoproterenol increased the lipolytic activity above basal concentrations at 10(-8) M and above. Lipolytic activity in T was significantly higher (P less than 0.01) than the S control at 10(-7) M and above. Epinephrine plus propranolol decreased lipolysis in both groups, but at 10(-5) M, lipolytic activity was significantly lower in S than in T (P less than 0.05). It is concluded that in female subjects, endurance training increases the sensitivity of subcutaneous abdominal adipose tissue to the lipolytic action of catecholamines; this effect seems to be related both to a decreased efficiency of the alpha 2-adrenergic pathway and to an increased efficiency of the beta-adrenergic pathway. This latter effect seems to take place at a step beyond the receptor-adenylate cyclase system in the lipolytic cascade.