Adrenergic receptors coupled to adenylate cyclase in human cerebromicrovascular endothelium

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Abstract
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 ß1 and ß2receptors (propranolol, atenolol, and butoxamine) and for α1-receptors (prazosin) dose-dependently blocked cAMP formation induced by the tested adrenergic agonists. Clonidine, an ga2>α1-agonist, also inhibited isoproterenol-stimulated production of cAMP while yohimbine (α2>α1 antagonist) augmented the norepinephrine or epinephrine-induced accumulation of cAMP. Cholera toxin-induced 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 (Gi) 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 ß1-, ß2-, α1 and α 2-adrenergic receptors linked to adenylate cyclase in endothelium derived from human brain microvasculature. These data also indicate that activation of endothelial α1 -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.