β-Adrenergic Regulation of Prostaglandin E2Receptors in Human and Rat Adipocytes*

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Abstract
Incubation of intact human and rat adipocytes with isoproterenol (10-6 M) inhibits the specific binding of [3H] prostaglandin E2 (PGE2) by .apprx. 25% in human adipocytes and 50% in rat adipocytes. Scatchard analysis of [3H]PGE2 binding demonstrated that the isoproterenol-induced decrease in receptor activity may be due to a decrease in the apparent number of PGE2-binding sites, while the receptor affinity was unaltered. The inhibitory effect of isoproterenol on [3H]PGE2 binding was already seen after 10 min of isoproterenol treatment; the maximal effect was obtained after 30-60 min. Half-maximal inhibition of binding occurred at a concentration of 5 x 10-8 M isoproterenol. The effect of isoproterenol could be mimicked by epinephrine, theophylline and (Bu)2 [dibutyl]-cAMP, indicating that elevated levels of cAMP are the common mechanism by which these agents affect PGE2 binding. The isoproterenol-induced inhibition of PGE2 binding was completely blocked by propranolol. The effects of some FFA [free fatty acids] and indomethacin were studied on PGE2 receptor binding, too. Apparently, endogenously released arachidonic acid could account for some of the reduction in PGE2 binding. A .beta.-adrenergic receptor-mediated cAMP-dependent mechanism for the regulation of PGE2 receptor binding is demonstrated in both human and rat adipocytes.
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