Sulpiride: a weak antagonist of norepinephrine and 5-hydroxytryptamine.

Antagonism of norepinephrine (NE) and 5-hydroxytryptamine (5-HT) by sulpiride was studied in vitro on rabbit aortic strips. Concentrations of sulpiride ranging from 3 X 10(-5) to 3 X 10(-3) M caused a progressive shift of the dose response curves of both NE and 5-HT to the right without inhibiting the responses to KCl. pA2 values of sulpiride calculated from Schild plots against NE and 5-HT were 4.6 and 4.4, respectively. Thus, sulpiride, which has been previously shown to be the most potent antagonist of the dopamine vascular receptors, is a very weak alpha-adrenergic or 5-HT antagonist.