PITUITARY-FUNCTION FOLLOWING SURGERY FOR PROLACTINOMAS

Preoperative and postoperative endocrine function studies were performed in 18 patients with prolactin-secreting tumors defined by hyperprolactinemia and abnormal sellar tomography. Preoperative testing showed decreased prolactin response to thyrotropin-releasing hormone (TRH); 9 of 18 patients had low basal serum LH and 11 of 15 patients had low urinary LH. In most patients follicle-stimulating hormone (FSH) was normal (serum, 13/18 and urine, 13/13). Five of 9 patients tested with luteinizing hormone-releasing hormone (LH-RH) had an exaggerated LH response and the rest were normal. The changes in gonadotropin secretion did not correlate with tumor size. In contrast, only patients with suprasellar extension showed deficiencies of thyroid hormone, or insulin-stimulated growth hormone (GH) or cortisol. Following surgery, 10 of 18 patients had normal serum prolactin. However, the prolactin response to TRH remained abnormal in 10 of 11 patients tested. Serum LH increased to normal in all patients whose prolactin values reverted to normal postoperatively. The GH values following provocative testing were higher postoperatively in the group as a whole and normalized in the patients with low GH values preoperatively. Clinical response did not correlate with tumor size; 3 of 5 patients with micro-adenomas recovered normal menses, while 5 of 8 patients with larger tumors resumed menses. Several of our findings may bear on the pathophysiology associated with these tumors. First, the TRH test results suggest that disordered prolactin secretion may persist after tumor removal. Second, the hypogonadotropic state in these individuals seems to represent a hypothalamic rather than a pituitary defect, i.e., the defect is observed in patients with small tumors, and pituitary responsiveness to LH-RH is normal or exaggerated. The resolution of clinical hypogonadism and disordered LH secretion after surgery is consistent with a direct effect of prolactin on the hypothalamic control of LH secretion.