Prolactin-secreting pituitary adenomas: prolactin dynamics before and after transsphenoidal surgery

Twenty women with hyperprolactinaemia secondary to a pituitary adenoma were studied before and after selective transsphenoidal removal of the tumour. Pre-operatively, thyrotrophin-releasing hormone (TRH) (200 micrograms iv) and metoclopramide (MCP) (10 mg po) did not produce a positive PRL response in the tumour patients. By contrast, 14 post-partum lactating women, who were used as controls, exhibited a positive response to MCP administration. Methergoline (4 mg po) was shown to decrease serum PRL levels in 8 normal subjects, in 6 puerperal women, and 9 of 10 tumour patients. Bromoergocriptine (CB-154, 2.5 mg po) decreased serum PRL levels in 10 tumour patients. Following transsphenoidal removal of the adenoma serum PRL levels were reduced in all patients, and returned to normal in 14 patients. Prognostics for completely normalizing PRL secretion after transsphenoidal surgery is bettery when initial serum PRL levels are below 200 ng/ml. After surgery all hyperprolactinaemic patients failed to show a positive PRL response to TRH and MCP. Nine normoprolactinaemic patients had a positive response to both stimuli while 3 patients failed to show a positive response immediately following surgery. Long-term studies, however, showed that a positive PRL response was obtained in all patients tested 8-14 months after treatment. A positive PRL response to methergoline and bromocriptine was observed post-operatively in the patients tested regardless of their basal PRL level. Data from this study indicate that surgically proven PRL-secreting adenomas are invariably associated with negative PRL responses to TRH and MCP. The normalization of the prolactin regulation after surgery points toward the intrapituitary localization of the lesion associated with PRL-secreting adenomas.