Methysergide induces selective potentiation in cholinergic contractions of the guinea-pig vas deferens by facilitating acetylcholine release.

Methysergide (3 x 10(-6) M) enhanced the contractile responses of the isolated stripped vas deferens of guinea-pig to acetylchline(ACh) and arecoline, but not those to noradrenaline, tyramine and bradykinin. Methysergide (3 x 10(-5) M) suppressed the contraction elicited by noradrenaline or histamine. The methysergide-induced potentiation of the response to ACh was prevented by pre-addition of hemicholinium but not by tetrodotoxin or morphine. The augmentation of the response to ACh by physostigmine was unaffected by hemicholinium. The phasic contraction of the tissue elicited by 30 mM KCl was also enhanced by methysergide, and this enhancement was prevented by the pre-addition of atropine (1.4 x 10(-7) M). In the depolarized vas deferens after exposure to 30 mM KCl, methysergide occasionally induced a sustained tonic contraction which was inhibited by atropine. These findings suggest that methysergide facilitates a release of ACh by acting on the cholinergic nerve terminals and selectively potentiates the cholinergic response.