EVIDENCE THAT THE POSTERIOR PITUITARY PLAYS A ROLE IN NEUROPEPTIDE-Y AND LUTEINIZING-HORMONE-RELEASING HORMONE-STIMULATED GONADOTROPIN-SECRETION IN-VITRO

Neuropeptide Y (NPY) has been shown to increase gonadotropin secretion directly at the level of the anterior pituitary (AP) in both the abse nce and the presence of luteinizing hormone-releasing hormone (LHRH). This is interesting because high-affinity I-125-NPY-binding sites have not been found in the AP. However, high-affinity I-125-NPY-binding si tes have been localized in the posterior pituitary (PP), and it has be en shown that removal of the PP alters luteinizing hormone (LH) secret ion in vivo, The following studies were conducted to determine if gona dotropin responsiveness to either NPY alone or to NPY in combination w ith LHRH was significantly different in AP cells cultured in the prese nce compared with the absence of PP cells. The studies indicated that NPY-induced LH secretion was significantly greater in the presence of PP cells, while follicle-stimulating hormone (FSH) secretion was not s ignificantly affected. LHRH-induced LH secretion was also significantl y greater in the presence of PP cells; however, LHRH-induced FSH secre tion was significantly decreased. NPY potentiated LHRH-induced LH secr etion in AP cells cultured in both the presence and the absence of PP cells; however, the degree of potentiation was not significantly diffe rent whether PP cells were present or absent. These results indicate t hat the PP may play a role in the responsiveness of the AP to NPY and to LHRH but plays no apparent role in NPY potentiation of LHRH respons iveness.