Persistence of impaired PRL responses to sulpiride in patients with PRL secreting pituitary adenomas after successful hypophysectomy.

TRH, arginine, L-dopa, and sulpiride tests for PRL secretion were carried out in 18 control subjects and 20 patients with pituitary PRL-secreting adenomas before and after hypophysectomy. After the hypophysectomy PRL levels fell to normal ranges in 9 cases (categorized as Group I), and remained high in 11 other cases (categorized as Group II). After the operation, there were no alterations of PRL responsiveness to TRH, arginine, or to L-dopa in terms of percent change from the basal value, in either Group I or Group II. No significant differences were found in PRL responses to the above three agents between operated Group I patients and normal subjects even when expressed in absolute values. On the other hand, the PRL responses to sulpiride in both Groups I and II improved markedly after the hypophysectomy, but the absolute response in operated Group I patients was still lower than that in normal subjects. The mean PRL value in operated Group I (mean +/- S.E., 13.2 +/- 0.8 ng/ml, n = 9) was significantly (p less than 0.01) higher than in normal subjects (5.1 +/- 0.4 ng/ml, n = 18). It is concluded 1) that even in hypophysectomized normoprolactinemic patients the circulating PRL may originate mainly from the residual tumor cells, and 2) that the sulpiride test is useful to detect the abnormalities of hypothalamo-pituitary axis in operated patients with PRL-secreting adenomas, whereas TRH, arginine, and L-dopa tests are less useful for such purposes.