Stimulating action of sulpiride and pimozide on prolactin release. Effect on bromocriptine, L-dopa and metergoline administration.

In order to evaluate the mechanism of action of metergoline, an antiserotonin agent, the effect of pre-treatment with metergoline on prolactin (PRL) release induced by sulpiride was compared to that obtained after bromocriptine administration in normal subjects. In addition, the metergoline effect on PRL release induced by pimozide, specific dopamine receptor blocking agent, was compared to that obtained with L-dopa. Metergoline administration resulted in definite decrease in plasma PRL in all subjects; however, metergoline did not block, differently from bromocriptine, the PRL release induced by sulpiride. On the contrary, metergoline, like L-dopa, inhibited PRL release induced by pimozide pre-treatment. These results raise the possibility that metergoline does not act as an antiserotonin agent; its antilactogenic effect observed under basal conditions may be dependent on different mechanisms of action.