ABNORMAL REGULATION OF PROLACTIN SECRETION AFTER SUCCESSFUL SURGERY FOR PROLACTIN-SECRETING PITUITARY TUMOURS

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Abstract
Patients with prolactin [PRL]-secreting pituitary tumors have a diminished PRL response after administration of a variety of stimulatory agents, including TRH, chlorpromazine (CPZ) and insulin-induced hypoglycemia. Responses to these agents were examined in 67 women with PRL-secreting tumors before and after trans-sphenoidal surgery. Of the women, 29 were cured as defined by restoration of normal serum PRL concentrations and resumption of regular menses. At 1 yr following trans-sphenoidal surgery, patients with normal PRL concentrations and regular menses had normal PRL responses to TRH, while the responses to CPZ and insulin hypoglycemia were not improved. The reversible impairment of PRL response to TRH reflects suppressed function of normal PRL-secreting cells, and the persistence of abnormal PRL responses to provocative stimuli after successful tumor removal may reflect some fundamental defect in the regulation of PRL secretion in patients with PRL-secreting adenomas. When growth hormone (GH) reserve after insulin hypoglycemia was represented as the mean absolute increment above the basal concentration and compared with normal subjects, women with PRL-secreting tumors had a diminished response that returned to normal after successful surgery. This reversible impairment of GH secretion is not adequately reflected by standard criteria for GH response and suggests that PRL may have a role in the regulation of GH secretion.