Defective regulation of prolactin secretion after successful removal of prolactinomas

The PRL response to nomifensine (Nom), an indirect DA agonist; domperidone (Dom), a DA receptor antagonist; and TRH, which directly stimulates the PRL-secreting cells, was evaluated 2-53 months after surgery in 13 patients in whom successful removal of a prolactinoma had resulted in normal serum PRL levels and return of regular menses or libido and potency. In addition, the pattern of TSH secretion in response to Dom and the spontaneous rise in plasma PRL of 6 cured patients during pregnancy were evaluated. Nom induced an inconsistent decrease in basal PRL levels, a pattern contrasting with that in healthy women in whom plasma PRL was markedly suppressed after administration of the drug. Dom and TRH elicited a significant rise of basal PRL levels, but the rise was markedly lower than that occurring in the control group. The TSH increment after Dom treatment was lower than that before surgery, though higher than that in the controls. Evaluation of individual patients showed that only one patient had a normal PRL response to either Nom or Dom, while the TSH response to the latter returned to normal in five of seven patients. During pregnancy, plasma PRL rose inconsistently in the patients, and PRL levels were generally lower than those in normal pregnant women. These results suggest the presence of an abnormality in the dopaminergic mechanism(s) of PRL control before and after adenomectomy or, less likely, the existence of impaired pituitary function or reserve.