Immunocytochemical evidence for gonadoliberin in rat anterior pituitary gland.

Endogenous gonadoliberin was localized by using immunocytological methods in the hypothalamic neurons which synthetize the peptide and in the hypophysial target cells. The rat tissues were fixed and frozen. Ultrathin sections were obtained by cryoultramicrotomy. In the pituitary gland, GnRH was observed in both gonadotropic and prolactin cells. In these cells, endogenous GnRH was observed in the secretory granules, in the cytoplasm and in the nucleus. After castration an increase of immunoreactive GnRH was observed; after injection of a potent agonist (D-Trp6-Pro9-Net-LRF) or an antagonist (D-pGlu1, D-Phe2, Trp3,6 LRF) endogenous GnRH staining was decreased. These data suggest that endogenous GnRH could be bound to a site having a high affinity for GnRH.