High resolution autoradiographic localization of LHRH receptors in the rat anterior pituitary using fixed sections

The cellular and subcellular localization of luteinizing hormone-releasing hormone (LHRH) receptors in rat anterior pituitary has been studied at the light and electron microscopic levels using in vitro autoradiography performed on fixed pituitary sections. The iodinated LHRH agonist [D-Ser(TBU)6,des-Gly-NH10(2)]LHRH ethylamide was used as the ligand. In semithin sections of pituitaries from castrated rats, specific labeling was exclusively localized over the castration cells. At the ultrastructural level, the analysis of silver grain distribution performed in gonadotrophs revealed that the plasma membrane, rough endoplasmic reticulum, and Golgi apparatus were significantly labeled. These findings are consistent with previous reports indicating the presence of specific LHRH binding sites in the plasma membrane. This is also the first demonstration that LHRH receptors are associated with intracytoplasmic organelles. Moreover, this ultrastructural technique should be very useful to localize with precision LHRH receptors in other organs, especially the brain.