Activation of alpha(2)-adrenergic receptors impairs exercise-induced lipolysis in SCAT of obese subjects

With the use of the microdialysis method, exercise-induced lipolysis was in vestigated in subcutaneous adipose tissue (SCAT) in obese subjects and comp ared with lean ones, and the effect of blockade of alpha(2) adrenergic rece ptors (ARs) on lipolysis during exercise was explored. Changes in extracell ular glycerol concentrations and blood flow were measured in SCAT in a cont rol microdialysis probe at rest and during 60-min exercise bouts (50% of he art rate reserve) and in a probe supplemented with the alpha(2)-AR antagoni st phentolamine. At rest and during exercise, plasma norepinephrine and epi nephrine concentrations were not different in obese compared with lean men. In the basal state, plasma and extracellular glycerol concentrations were higher, whereas blood flow was lower in SCAT of obese subjects. During exer cise, the increase of plasma glycerol was higher in obese subjects (115 +/- 35 vs. 65 +/- 21 mu mol/l). Oppositely, the exercise-induced increase in e xtracellular glycerol concentrations in SCAT was five- to sixfold lower in obese than in lean subjects (50 +/- 14 vs. 318 +/- 53 mu mol/l). The exerci se-induced increase in extracellular glycerol concentration was not signifi cantly modified by phentolamine infusion in lean subjects but was strongly enhanced in the obese subjects and reached the concentrations found in lean sujects (297 +/- 46 mu mol/l). These findings demonstrate that the physiol ogical stimulation of SCAT adipocyte alpha(2)-ARs during exercice-induced s ympathetic nervous system activation contributes to the blunted lipolysis n oted in obese men.