Independence of the effects of epinephrine, glucagon, and adrenocorticotropin on glucose utilization from those on lipolysis in isolated rat adipose cells.

The stimulatory effects of epinephrine, glucagon, and adrenocorticotropin (ACTH) upon lipolysis and on the uptake and oxidation of glucose were studied in isolated rat epididymal adipocytes. Under conditions in which prostaglandin El (PGE1) and nicotinic acid were antilipolytic against epinephrine, these agents were without influence on the effects of the hormone on the metabolism of glucose. Furthermore, the synergistic effects of caffeine and theophylline on epinephrine-induced lipolysis were not seen in studies of epinephrine-stimulated glucose oxidation. Since epinephrine increased the uptake and oxidation of glucose under conditions which either did (presence of bovine sermn albumin) or did not (absence of bovine serum albumin) permit accumulation of free fatty acids, it is unlikely that free fatty acids mediate the effects of epinephrine on glucose entry and oxidation in adipocytes. Since two fl-adrenergic blocking agents, KS 592 and propranolol, inhibited epinephrine’s stimulation of both lipolysis and glucose oxidation, it appears that both effects of the hormone involve p-receptors. While PGEr, KS 592, and propranolol all inhibited the stimulatory effects of glucagon and ACTH on lipolysis in adipocytes, neither agent influenced the action of either hormone on glucose oxidation; the latter finding suggests that P-receptors do not mediate the stimulatory effects of these hormones on glucose oxidation. Ka 592 and propranolol were several orders of magnitude more potent as antilipolytic agents against epinephrine than they were against ACTH and glucagon. Excessive amounts of PGEr only partially inhibited the lipolytic effect of even submaximal concentrations of epinephrine, glucagon, and ACTH in adipocytes, although total inhibitions were obtainable with appropriate concentrations of the P-adrenergic blocking compounds. Such observations suggest that the adenyl cyclase system for the synthesis of adenosine 3’,5’-cyclic monophosphate in adipocytes contains at least two different types of activation receptor sites for hormones, and that PGEr binds to only one type of site