[Various aspects of dopaminergic function in patients with prolactin-secreting hypophyseal adenoma]

Controversial data have been published in these last years on the dopaminergic tonus of tubero infundibular (TIDA) neurons in hyperprolactinemic subjects. Some authors retain that L-Dopa (LD) stimulation test after pretreatment with Carbidopa (CD), a dopa decarboxylase inhibitor substance, may reveal the presence of a central Dopamine (DA) defect in patient with prolactinoma. To elucidate the reason of so different activity of DA central tonus in subjects with prolactinoma, the effects of Nomifensine (NOM), an indirect DA agonist, DOM, Carbidopa/L-Dopa (CD/LD) and LD, were studied in 26 prolactinoma patients, (basal Prl levels 50 to 280 ng/ml). The patients (24-39 years) were characterized by secondary amenorrhea with sella turcica enlargement at hypocicloidal polytomography. The NOM administration resulted unable to reduce Prl plasma levels in all the patients. On the basis of Prl response to CD/LD administration the patients were subdivided in two groups: group A, which showed a significant decrease of Prl plasma levels and group B, who did not show any significant change. LD test induced a significant Prl decrease in all patients with more evident response in these of group A. DOM administration induced a Prl rise in patients of group A, but failed to change significantly Prl levels in group B subjects. These results confirming the high validity of NOM inhibiting test in the diagnosis of tumoural hyperprolactinemic states, reveal contradictory responses to CD/LD, LD and DOM, with sustain the existence of 2 sub-group of Prolactinomas: with or without a maintained DA central tonus supporting the possibility of different etiopathogenetical factors in inducing a tumoural hyperprolactinemic states.