b-Adrenergic regulation of lipolysis and blood flow in human skeletal muscle in vivo

Hagström-Toft, Eva, Staffan Enoksson, Erik Moberg, Jan Bolinder, and Peter Arner. b-Adrenergic regulation of lipolysis and blood flow in human skeletal muscle in vivo. Am. J. Physiol. 275 (Endocrinol. Metab. 38): E909–E916, 1998.— Little is known about the regulation of catecholaminestimulated lipolysis in human skeletal muscle. Therefore, b-adrenergic regulation of lipolysis and blood flow was investigated in healthy subjects in vivo by use of microdialysis of the gastrocnemius muscle. First, during a hypoglycemic, hyperinsulinemic clamp, which induces a lipolytic response in skeletal muscle tissue, the muscle was locally perfused with b-adrenoceptor blocking agents. Perfusion with nonselective (propranolol) and b2-selective (ICI-118551) blocking agents counteracted the hypoglycemia-induced lipolysis (P , 0.01), but perfusion with metoprolol (b1-blocker) did not affect the glycerol response. Second, selective b-adrenoceptor agonists were perfused in situ into skeletal muscle during resting conditions. b2-Adrenoceptor stimulation with terbutaline induced a concentration-dependent increase in skeletal muscle glycerol levels and in tissue blood flow, whereas perfusion with b1or b3-adrenoceptor agonists (dobutamine or CGP12177) did not influence the glycerol concentration or blood flow. In conclusion, in skeletal muscle tissue, only the b2subtype is of importance among b-adrenoceptors for regulation of lipolysis and blood flow. This is in contrast to adipose tissue, where b1and b3-adrenoceptors are also involved.