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 antilipolytic alpha(2)-adrenergic receptor pathway in the regulation of lipolysis during exercise in subcutaneous abdominal adipose tissue (SCAAT). Seven trained men and 15 untrained men were studied. With the use of microdialysis, the extracellular glycerol concentration was measured in SCAAT at rest and during 60 min of exercise at 50% of maximal oxygen consumption. One microdialysis probe was perfused with Ringer solution; the other was supplemented with phentolamine (alpha(2)-adrenergic receptor antagonist). No differences in baseline extracellular or plasma glycerol concentrations were found between the two groups. The exercise-induced extracellular and plasma glycerol increase was higher in trained compared with untrained subjects (P < 0.05). Addition of phentolamine to the perfusate enhanced the exercise-induced response of extracellular glycerol in untrained subjects but not in trained subjects. The exercise-induced increase in plasma norepinephrine and epinephrine 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 trained subjects, the alpha(2)-mediated antilipolytic action is not involved in the regulation of lipolysis in SCAAT during exercise.