Abstract
The effect of dopamine on adenylate cyclase activity was investigated in slices of human term placentas. Dopamine elicited a dose-dependent stimulation of cAMP formation with a ED 50 value of about 1 × 10 −6M dopamine and an increase of 110 % over the control with 1 × 10 −4M dopamine. (-)-Epinephrine and (-)-norepinephrine also increased placental cAMP formation. Apomorphine displayed a slight but non-significant stimulatory effect while bromocryptine was not effective. SCH 23390, a selective antagonist of dopamine D 1 receptors caused a dose-dependent decrease of the dopamine activation. In contrast, the dopamine increase of cAMP was unaffected by β - and α-adrenergic blocking drugs and by the D 2 selective antagonist, (-)-sulpiride. These data indicate that dopamine stimulates cAMP formation in human term placenta through a specific mechanism via D 1 dopaminergic receptors positively coupled to adenylate cyclase.
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