Lack of alpha(2)-adrenergic antilipolytic effect during exercise in subcutaneous adipose tissue of trained men

The aim of this study was to investigate the involvement of the antilipolyt ic alpha (2)-adrenergic receptor pathway in the regulation of lipolysis dur ing exercise in subcutaneous abdominal adipose tissue (SCAAT). Seven traine d men and 15 untrained men were studied. With the use of microdialysis, the extracellular glycerol concentration was measured in SCAAT at rest and dur ing 60 min of exercise at 50% of maximal oxygen consumption. One microdialy sis probe was perfused with Ringer solution; the other was supplemented wit h phentolamine (alpha (2)-adrenergic receptor antagonist). No differences i n baseline extracellular or plasma glycerol concentrations were found betwe en the two groups. The exercise-induced extracellular and plasma glycerol i ncrease was higher in trained compared with untrained subjects (P < 0.05). Addition of phentolamine to the perfusate enhanced the exercise-induced res ponse of extracellular glycerol in untrained subjects but not in trained su bjects. The exercise-induced increase in plasma norepinephrine and epinephr ine concentrations and the decrease in plasma insulin were not different in the two groups. These in vivo findings demonstrate higher exercise-induced lipolysis in trained compared with untrained subjects and show that, in tr ained subjects, the <alpha>(2)-mediated antilipolytic action is not involve d in the regulation of lipolysis in SCAAT during exercise.