Identification and characterization of adrenergic receptors and catecholamine-stimulated adenylate cyclase in hog pial membranes

Abstract

In order to define the adrenergic receptors in small pial blood vessels, we studied [ 3H]dihydroalprenolol (DHA) binding, [ 3H]dihydroergocryptine (DHE) binding, and catecholamine-stimulated adenylate cyclase in membranes prepared from the hog pia. [ 3H]DHA bound to a saturable number of sites (0.09 pmol/mg protein) with a high affinity (10 nM). The ability of a small series of adrenergic agents to compete for [ 3H]DHA binding was as expected for binding to β-adrenergic membrane receptors. The receptor binding appeared to be composed largely ofβ 2-adrenergic sites but some sites withβ 1 properties were detected. The β-adrenergic agonist, isoproterenol, stimulated adenylate cyclase activity by 20% in pial membranes in the presence of GTP. The potency of catecholamines in stimulating adenylate cyclase correlated well with their ability to compete for [ 3H]DHA binding. [ 3H]DHE also bound to a saturable number of sites (0.39 pmol/mg) on these membranes. α-Adrenergic agents were potent competitors for [ 3H]DHE binding but dopamine, serotonin and histamine had effects only at high concentrations. These data demonstrate the presence of α- and β-adrenergic membrane receptors and β-adrenergically stimulated adenylate cyclase activity in small pial blood vessels from the hog.