Cultured endothelium derived from three microvascular fractions of human brain was used to characterize adrenergic receptors coupled to adenylate cyclase activity. Catecholamines (norepi- nephrine, epinephrine) and their analogs (isoproterenol, phenylephrine, 6-fluoronorepinephrine) dose-dependently stimulated endothelial production of cAMP. Antagonists for betal and beta2 receptors (propanolol, atenolol, and butoxamine) and for alphal- receptors (prazosin) dose-dependently blocked cAMP formation induced by the tested adrenergic agonists. Clonidine, the selective alpha2 agonist, also inhibited isoproterenol-stimulated production of cAMP, while yohimbine (alpha2-antagonist) augmented the norepinephrine or epinephrine-induced accumulation of cAMP. Cholera toxin ADP ribosylation of the stimulatory guanine nucleotide-binding protein (GS) abolished the stimulatory effect of norepinephrine, epinephrine, phenylephrine or 6-fluoronorepinephrine on cAMP formation. ADP ribosylation of the inhibitory guanine nucleotide binding protein (G1) by pertussis toxin had no effect on either phenylephrine or 6-fluoronorepinephrine-induced production of cAMP while it increased the norepinephrine and epinephrine-induced accumulation of cAMP. These findings represent the first documentation of beta1, beta2-, alphal-, and alpha2-adrenergic receptors linked to adenylate cyclase in endothelium derived from human brain microvasculature. The data also indicate that activation of endothelial alpha1-adrenergic receptors is mediated by a signal transduction mechanism associated with Gs protein. The results strongly support the presence of various receptor-controlled adrenergic regulatory mechanisms on human cerebromicrovascular endothelium.
