INTRACELLULAR GONADOTROPIN-RELEASING-HORMONE IMMUNOREACTIVITY IN GONADOTROPHS OF INTACT OR CASTRATED MALE-RATS - SEMIQUANTITATIVE ESTIMATION OF TESTOSTERONE AND GNRH ANTAGONIST TREATMENT

Changes in intracellular gonadotropin-releasing hormone (GnRH) immunor eactivity (GnRH-IR) in pituitary gonadotrophs were assessed by the use of a semiquantitative immunocytochemical method in male rats undergoi ng various manipulations known to greatly modify gonadotropin secretio n. In basal conditions, immunoreactive GnRH was localized in the cytop lasmic matrix, the secretory granules and the nucleus of these cells. Following intravenous stimulation with GnRH (100 ng i.v.), the GnRH-IR increased rapidly in all these three subcellular compartments, peakin g at 15 min. In untreated, long-term castrated rats, GnRH-IR increased both in the basal state and after administration of GnRH. Injection o f the castrated rats with testosterone propionate reduced the observed GnRH-IR to the level observed in intact rats. Acute or chronic treatm ent of castrated rats with a potent GnRH antagonist rendered GnRH-IR c ompletely undetectable in all the three previously positive subcellula r compartments of gonadotrophs, and GnRH-IR did not reappear after sti mulation with GnRH. In sum, the fact that modifications of GnRH immuno reactivity are observed in rat gonadotrophs: (1) confirms the GnRH int ernalization process; (2) suggests different sites of action for GnRH within the cell, and (3) demonstrates rapid clearance of intracellular GnRH after stimulation.