Tests of prolactin secretion in the diagnosis of hyperprolactinemic states: nomifensine and domperidone.

Forty-one subjects with hyperprolactinemia underwent testing on separate occasions with nomifensine, an indirectly acting dopamine agonist, and domperidone, a dopamine receptor-blocking agent. Nomifensine (200 mg orally) did not significantly modify plasma levels of prolactin (PRL) in 17 subjects in whom the existence of a pituitary tumor had been established at surgery (12 subjects) or was highly probable (5 subjects). Of the remaining 24 patients with hyperprolactinemia of uncertain etiology, 6 had PRL responsiveness to nomifensine (decrease of baseline PRL levels greater than or equal to 30%) and 18 had PRL unresponsiveness to the drug. The administration of domperidone (4-mg bolus injected intravenously) showed in 36 of the 41 patients the existence of a homogeneity between PRL responsiveness to nomifensine and PRL responsiveness to domperidone. In only five patients was failure of nomifensine to lower plasma PRL levels associated with an increase in plasma PRL levels after domperidone administration (at least doubling of baseline PRL levels). The combined application of nomifensine and domperidone tests holds promise of being a useful method for distinguishing among hyperprolactinemic subjects those with a prolactinoma.