Induction of testicular gonadotropin-releasing hormone (GnRH) receptors by GnRH: effects of pituitary hormones and relationship to inhibition of testosterone production.

Abstract

In vivo administration of gonadotropin-releasinghormone (GnRH) inhibits testosterone production in intact rats and increases testicular GnRH receptors. To delineate the relationship of these effects and to determine whether GnRH induced its testicular receptor by an extrapituitary mechanism, GnRH and LH receptors were studied in intact or hypophysectomized (H) rats. Adult, H, or sham-operated (S) males were injected with GnRH (6.7 μg every 8 h for 1, 2, 4, and 6 days). Some H rats were also treated with GH and PRL (150 μg/day) to maintain LH receptors. Decapsulated testes were assayed for GnRH and LH receptors or incubated to assess testosterone production in the presence or absence of hCG. GnRH treatment in S rats resulted in a biphasic change in GnRH receptor numbers. The basal receptor concentration (212 ± 27 fmol /mg protein) increased to a peak at 2 days (501 ± 32 fmol/mg) before declining to control values after 6 days of treatment. GnRH receptors increased 2-fold 1 day after hypophysectomy (449 ± 5...