Cultured endothelium derived from three fractions of human cerebral microvessels was used to characterize dopamine (DA) receptors linked to adenylate cyclase activity. Dopamine or D1-agonists [SKF -38393, R(+-), SKF -82958(+-) HBR] stimulated endothelial cAMP formation in dose - dependent manner. The selective D1 -antagonist [SCH -23390, R(+-)] dose -dependently inhibited the DA or D1 -agonists stimulated production of cAMP. The selective D2 -antagonist [sulpiride, S (-)] inconsistently augmented the DA stimulatory effect on cAMP formation in all three endothelial fractions. The sensitivity of endothelial adenylate cyclase was greater in endothelium derived from large and small microvessels than from capillaries. Agonists of alpha-1 adrenergic receptors (phenylephrine, 6 -fluoronorepinephrine) or serotonin (5-HT) which stimulated the production of cAMP by itself did not augment the DA-stimulated cAMP formation. On the contrary, alpha1-adrenergic agonists or 5-HT incubated with DA reduced the cAMP production which could be partially blocked by 5HT2- or D2-antagonists, respectively. These findings represent the first demonstration of D1 -(stimulatory) and D2 - (inhibitory) receptors linked to adenylate cyclase in microvascular endothelium derived from human brain. The data also indicate that dopaminergic receptors can interact with either alpha1-adrenergic or 5-HT receptors in endothelium on the adenylate cyclase level.
