Metiamide potentiates the stimulant actions of sympathomimetic amines "in vitro".

Metiamide significantly potentiated the contractions of the guinea-pig and the rat vas deferens and seminal vesicle produced by noradrenaline, dopamine and methoxamine. The responses to acetylcholine and carbachol were not affected by metiamide. Tetrodotoxin did not affect metiamide-induced potentiation of the sympathomimetics. Potentiation induced by metiamide was Ca++-dependent. Mepyramine failed to influence the responses to the amines. It is suggested thaat extra-neuronal mechanisms may be involved in the interactions of metiamide and sympathomimetics.