Catecholamine-sensitive adenylate cyclase of human fat cell ghosts: a comparative study using different beta-adrenergic agents.

Some of the effects of beta-adrenergic agonists and antagonists on the adenylate cyclase system of human fat cell ghosts were studied. Isoproterenol, by causing about a fourfold increase of enzyme activity, was more potent than epinephrine and norepinephrine (about 2.5--3.0-fold stimulation). The beta2-adrenergic agonists salbutamol, terbutalin, and fenoterol were considerably less effective than the naturally occurring catecholamines. The stimulatory actions of isoproterenol and beta2-adrenergic agonists were competitively inhibited by the beta-blocking agent propranolol. Isoproterenol stimulation was also inhibited by the selective beta1-adrenergic antagonist practolol. This compound, however, was less potent than propranolol. The results are suggestive for an adenylate cyclase system in human fat cell ghosts coupled to beta1-adrenergic receptor sites. These receptors differ from the cardiac beta receptors with respect to practolol affinity.