Sequential prolactin evaluation of a "cured" patient with recurrence of prolactinoma

Several investigators have suggested that prolactin secretion in some subjects with hyperprolactinemia associated with pituitary macroadenomas may have a resistance to the prolactin inhibitory hormone, dopamine. This report describes a male subject with a prolactinoma whose preoperative evaluation demonstrated a resistance of prolactin release to inhibition by dopamine. Evaluation of prolactin secretion from monolayer culture of his tumor also revealed a resistance to inhibition by dopamine. Four months postoperatively, normal serum prolactin levels and a normal maximal inhibition of prolactin to a dopamine infusion of 0.04 microgram/kg/minute suggested surgical cure. However, a 24-hour prolactin sampling revealed blunted nocturnal augmentation of prolactin release, an early escape of inhibition of prolactin release at 150 minutes from a 0.04 microgram/kg/minute dopamine infusion, and abnormal prolactin response to a low-dose (0.004 microgram/kg/minute) dopamine infusion. Hence, persistent abnormalities in prolactin secretory dynamics were noted with more extensive testing in this patient when he was thought to have been cured. One year postoperatively, the hyperprolactinemia recurred, prolactin release was markedly resistant to dopamine, and an abnormal 24-hour prolactin profile of release was present. Thus, resistance of prolactin secretion to inhibition by dopamine was present in this patient with a prolactinoma. Additionally, an abnormal prolactin response to dopamine was noted to precede the development of hyperprolactinemia with tumor recurrence.