Pituitary gonadotropin response in women with idiopathic hyperprolactinemia

Inappropriate lactation and idiopathic hyperprolactinemia are frequently associated with amenorrhea. In these individuals, peripheral levels of follicle-stimulating hormone (hFSH) are usually normal, and luteinizing hormone (hLH) levels are often found in the low-normal range. The present study was undertaken to evaluate the functional capacity of the pituitary by the response of hFSH and hLH to synthetic gonadotropin-releasing hormone (Gn-RH). Six women with amenorrhea, inappropriate breast secretion, and idiopathic hyperprolactinemia (prolactin levels ranged from 45 to 355 ng/ml) were given 100 mug of Gn-RH intramuscularly. Serum hFSH and hLH levels were assessed in samples obtained at 15-minute intervals over the next 2-hour period. Initial hFSH levels were normal in all women, with a mean of 242 +/- 72 ng/ml. The absolute increase after Gn-RH administration averaged 486 +/- 193 ng/ml. Serum hLH was below normal in three of the six women, and normal in the remaining three women initially. The absolute increase averaged 1308 +/- 315 ng/ml. The greatest percentage increase in hLH was found in the women with the subnormal basal titers. In these women, hLH rose from a mean of 22 ng/ml to a mean of 1092 ng/ml. These data demonstate an exaggerated increase in hFSH and hLH levels after exogenous Gn-RH administration. This suggests that the amenorrhea associated with elevated serum prolactin levels is principally of hypothalamic origin.