ADRENERGIC-RECEPTORS COUPLED TO ADENYLATE-CYCLASE IN HUMAN CEREBROMICROVASCULAR ENDOTHELIUM

Cultured endothelium derived from three microvascular fractions of human brain was used to characterize adrenergic receptors coupled to adenylate cyclase activity. Catecholamines (norepinephrine, epinephrine) and their analogs (isoproterenol, phenylephrine, 6-fluoronorepinephrine) dose-dependently stimulated endothelial production of cAMP. Antagonists for beta1 and beta2 receptors (propranolol, atenolol, and butoxamine) and for alpha1 receptors (prazosin) dose-dependently blocked cAMP formation induced by the tested adrenergic agonists. Clonidine, an alpha2>alpha1-agonist, also inhibited isoproterenol-stimulated production of cAMP while yohimbine (alpha2>alpha1 antagonist) augmented the norepinephrine or epinephrine-induced accumulation of cAMP. Cholera toxin-induced ADP ribosylation of the stimulatory guanine nucleotide binding protein (G(s)) abolished the stimulatory effect of norepinephrine, epinephrine, phenylephrine or 6-fluoronorepinephrine on cAMP formation. ADP ribosylation of the inhibitory guanine nucleotide binding protein (G(i) 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-, alpha2 and alpha2-adrenergic receptors linked to adenylate cyclase in endothelium derived from human brain microvasculature. These data also indicate that activation of endothelial alpha1-adrenergic receptors is mediated by a signal transduction mechanism associated with G(s) protein. The results strongly support the presence of various receptor-controlled adrenergic regulatory mechanisms on human cerebromicrovascular endothelium.