Stimulatory effect of the dopa decarboxylase inhibitor Ro 4-4602 on prolactin release: inhibiton by L dopa, metergoline, methysergide and 2 Br α ergocryptine

In order to evaluate the role of serotonin (5 HT) in the effect of L dopa on prolactin (PRL) release, normal subjects received L dopa alone or L dopa plus a dopa decarboxylase inhibitor (Ro 4 4602) in basal conditions and following the repeated administration of metergoline, a specific anti 5 HT agent. The inhibiting effect of L dopa on PRL levels was enhanced by metergoline. On the contrary, L dopa plus Ro 4 4602 induced a sharp increase in serum PRL levels. This effect was completely abolished by metergoline, which also significantly reduced fasting PRL levels in all the subjects studied. Ro 4 4602 alone induced a significant increase in serum PRL levels, similar to that commonly observed with chlorpromazine and TRH. The effect was similar in males and in females and was reproducible in experiments performed on different days. The effect of Ro 4 4602 was completely abolished by 2 Br α ergocryptine and metergoline, and, to a lesser degree, was reduced by methysergide. These results suggest that Ro 4 4602 is a reliable stimulus to PRL release and show that any stimulus to PRL secretion may be blocked by both dopaminergic and anti serotonin agents