Human adipose tissue blood flow during prolonged exercise, III. Effect of beta-adrenergic blockade, nicotinic acid and glucose infusion.

Subcutaneous adipose tissue blood flow (ATBF) was measured in six male subjects by the 133Xe-washout technique during 3-4 h of exercise at a work load corresponding to an oxygen uptake of about 1.71/min. The measurements were done during control conditions, during blockade of lipolysis by nicotinic acid, during acute i.v. beta-adrenergic blockade by propranolol, and during continuous i.v. infusion of glucose. The most pronounced lipid mobilization and utilization during work was seen in the control experiments where ATBF rose 3-fold on average from the initial rest period to the third hour of work. No increase in lipolysis and no increase in ATBF were found when lipolysis was blocked by nicotinic acid (0.3 g/h). Propranolol treatment (0.15 mg/kg) reduced lipolysis and nearly abolished the increase in ATBF during exercise. Intravenous administration of glucose (about 0.25 g/min) did not influence lipid metabolism (evaluated by the respiratory quotient) nor did it reduce the ATBF response to exercise. These results are inconsistent with the hypothesis that increase in ATBF during exercise is elicited via direct stimulation of vascular beta1-receptors, while they are not in disagreement with the hypothesis that adipose tissue vasodilation during exercise is secondary to metabolic events connected to lipolysis.