Dynamics of alpha-adrenergic inhibition of the adenyl cyclase-cyclic amp system in human adipose tissue.

In short-term incubations of fat cells isolated from human adipose tissue, noradrenaline (0.2-2x10--5 M), a mixed alpha and beta-adrenergic agonist, stimulated only slightly cyclic AMP accumulation. In the presence of the alpha-adrenergic blocking agent phentolamine (0.05-5mug/ml), noradrenaline markedly augmented the amount of labelled cyclic nucleotide. The stiumlatory effect of noradrenaline and noradrenaline plus phentolamine was abolished by propranolol (0.1-10 mug/ml). Theophylline (10--4-10--3 M) slightly increased the (3-H) cyclic AMP levels per se and magnified the stiumulatory action of other agents, but did not mimic the potentiating effect of phentolamine on noradrenaline action.