Characteristics of the lipolytic beta-adrenergic receptors in hamster adipocytes

Hamster adipocyte beta-adrenergic receptors were characterized by the effect on the lipolysis rate of several selective beta-adrenergic agonists and antagonists. Prenalterol and procaterol, selective beta 1- and beta 2-agonists, respectively, both stimulated the lipolysis rate half-maximally at 1-2 microM, a concentration approximately 100-fold higher than that needed for half-maximal stimulation by isoprenaline. The maximal procaterol effect was similar to that of isoprenaline, while the effect of prenalterol was 40% lower. Submaximally isoprenaline-stimulated lipolysis was half-maximally inhibited by propranolol at 0.2 microM and by atenolol and H 35/25, selective beta 1- and beta 2-antagonists, at 23 and 6 microM concentration, respectively. Highly specific beta 1 and beta 2 stimulation was induced by incubation with prenalterol or procaterol, with simultaneous maximal selective beta 2 or beta 1 inhibition, respectively. The maximal beta 2 stimulation was approximately twice the corresponding beta 1 effect under these conditions, the sum of both effects closely approaching that of maximal nonselective beta-adrenergic stimulation with isoprenaline. Similar results were obtained with the selective beta 2-antagonist, ICI 118,551, or the beta 1-antagonists, pamatolol and practolol. The findings are most easily explained by the existence of a heterogeneous beta 1- and beta 2-adrenergic receptor population on hamster adipocytes.