Abstract
This study was designed to assess whether physiological activation of the sympathetic nervous system induced by exercise changes adipose tissue responsiveness to catecholamines in humans. Lipid mobilization in abdominal subcutaneous adipose tissue was studied with the use of a microdialysis method in 11 nontrained men (age: 22.3 +/- 1.5 yr; body mass index: 23.0 +/- 1.6).
Adipose tissue adrenergic sensitivity was explored with norepinephrine, dobutamine (beta (1)-agonist), or terbutaline (beta (2)-agonist) perfused during 30 min through probes before and after 60-min exercise (50% of the maximal aerobic power). The increase in extracellular glycerol concentration during infusion was significantly lower after the exercise when compared with the increase observed before the exercise (P < 0.05, P < 0.02, and P < 0.01, respectively, for norepinephrine, dobutamine, and terbutaline).
In a control experiment realized without exercise, no difference in norepinephrine-induced glycerol increase between the two infusions was observed. To assess the involvement of catecholamines in the blunted -adrenergic-induced lipolytic response after exercise, adipose tissue adrenergic sensitivity was explored with two 60-min infusions of norepinephrine or epinephrine separated by a 60-min interval.
With both catecholamines, the increase in glycerol was significantly lower during the second infusion (P, 0.05). The findings suggest that aerobic exercise, which increased adrenergic activity, induces a desensitization in beta (1)- and beta (2)-adrenergic lipolytic pathways in human subcutaneous adipose tissue.