Rat testis LH/hCG recptors and testosterone production after treatment with GnRH

Adults male rats were implanted subcutaneously for 1, 2 or 4 days with Alzet osmotic minipumps, infusing synthetic gonadotropin-releasing hormone (GnRH) at a rate of 0.1 microgram/h. Plasma LH increased significantly, reaching a maximum after 2 days treatment. Plasma and testicular testosterone levels increased to a maximum in 1 day, and decreased gradually thereafter, reaching the control level by day 4. Testicular specific [125I]hCG binding decreased gradually during the treatment, being 57% of the controls by day 4. It is concluded that changes of physiologic magnitude in circulatory LH are able to induce a significant loss of testicular LH/hCG binding capacity. Furthermore, after a short stimulatory phase there is a lack of response in testicular steroidogenesis to the elevated LH levels.