B-adrenergic regulation of lipolysis and blood flow in human skeletal muscle in vivo

Little is known about the regulation of catecholamine-stimulated lipolysis in human skeletal muscle. Therefore, beta-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 beta-adrenoceptor blocking agents. Perfusion with nonselective (propranolol) and beta(2)-selective (ICI-118551) blocking agents counteracted the hypoglycemia-induced lipolysis (P < 0.01), but perfusion with metoprolol (beta(1)-blocker) did not affect the glycerol response. Second, selective beta-adrenoceptor agonists were perfused in situ into skeletal muscle during resting conditions. beta(2)-Adrenoceptor stimulation with terbutaline induced a concentration-dependent increase in skeletal muscle glycerol levels and in tissue blood flow whereas perfusion with beta(1)- or beta(3)-adrenoceptor agonists (dobutamine or CGP-12177) did not influence the glycerol concentration or blood flow. In conclusion, in skeletal muscle tissue, only the beta(2)-subtype is of importance among beta-adrenoceptors for regulation of lipolysis and blood flow This is in contrast to adipose tissue, where beta(1)- and beta(3)-adrenoceptors are also involved.