Pituitary responsiveness to luteinizing-hormone-releasing hormone in different reproductive disorders. A review

As a result of the use of synthetic luteinizing-hormone-releasing hormone (LHRH) (and its analogs), significant advances in modern clinical practice are being realized. We studied the use of LHRH as a test for pituitary reserve for gonadotropin secretion in different reproductive disorders. Synthetic LHRH was used as a diagnostic test for discriminating pituitary from hypothalamic disorders. After appropriate LHRH priming of the pituitary, LHRH was used to document hypothalamic dysfunction in patients with Kallmann's syndrome who had normal gonadotropin responsiveness to LHRH. The gonadotropin responsiveness to 100 micrograms of LHRH was impaired or absent in patients with panhypopituitarism, craniopharyngiomas, hemochromatosis and acromegaly accompanied by abnormal lactation. In women with gonadal dysgenesis, the absence of gonadal steroid feedback exacerbated the pituitary responsiveness to LHRH. Women with hyperprolactinemia are also known to have a blunted gonadotropin response to endogenous and exogenous LHRH. An experimental rat model was developed in our laboratory to study the site of prolactin action on gonadotropin secretion. LHRH challenge tests during perphenazine-induced hyperprolactinemia in rats indicated that prolactin may decrease pituitary sensitivity to LHRH. Additional experiments indicated that the increased progesterone produced in these hyperprolactinemic (pseudopregnant) rats was probably responsible for the decreased pituitary responsiveness to LHRH. Further studies will be necessary to determine whether prolactin, which can alter ovarian steroidogenesis in vitro, interferes with ovulation directly in addition to affecting the hypothalamic-pituitary axis.