Changes in pituitary hormones during and following transsphenoidal removal of prolactinomas

Prolactin (PRL) and other pituitary hormones (luteinizing hormone, follicle-stimulating hormone, growth hormone [GH], thyrotropin stimulating hormone) were measured before, during, and after transphenoidal pituitary adenomectomy in 16 patients with hyperprolactinemia. The diagnosis of prolactinoma was made in three of the 16 patients by the absence of PRL response to thyrotropin-releasing factor (TRF) and a dopamine receptor antagonist, metoclopramide, without radiologic evidence of an adenoma. Contrary to findings in subjects with normal PRL values, the PRL rise in response to anesthesia and operation was absent. Other pituitary hormones, with the exception of GH, which increased during anesthesia and operation, exhibited no acute changes. In 11 of 16 cases, complete tumor removal was achieved as determined by the rapid decline of PRL levels to normal values within 24 to 48 hours after operation and by subsequent clinical follow-up. This finding documents that the adenoma is the main source of excessive PRL secretion. The circulating half time of immunoreactive PRL determined by frequent sampling in these patients was variable, ranging from 74 to 190 minutes, significantly longer than the previously reported value of 15 minutes determined by bioassay. Although a transient decline was evident, serum PRL levels remained elevated in those patients with incomplete tumor removal. These findings suggest that a single measurement of serum PRL within 24 to 48 following transphenoidal adenomectomy is a reliable indicator of the success or failure of the procedure.