Effects of medroxyprogesterone acetate or gonadotrophin-releasing hormone agonist on suppression of spermatogenesis in the dog (Canis familiaris).

Medroxyprogesterone acetate (MPA) was administered as a depot injection to two adult male dogs. One was injected with 75 mg as a depot injection once a month for 2 months and the other with 50 mg at 2-weekly intervals for 1 month, followed by 100 mg at 2-weekly intervals for a further 2 months. Two other male beagles were given gonadotrophin-releasing hormone (GnRH) agonists (nafarelin derivative no. 49947 and nafarelin acetate) at a dose of 50 micrograms day-1 for either 22 or 23 days. The profiles of luteinizing hormone (LH) and testosterone were monitored before and during the treatment periods, and changes in the dogs' testes, epididymides and prostate glands were determined post mortem. In the MPA-treated animals, LH was suppressed for only very brief periods. In contrast, in the dogs treated with GnRH agonist, LH and testosterone concentrations were suppressed for most of the treatment period. In the MPA-treated animals, histological changes were seen mainly in the head of the epididymis, and in the acrosome region of the spermatozoa still present in this region of the male reproductive tract. The acrosome, instead of being closely applied to the sperm head, was in contact only in the most anterior areas, with the remainder forming a fan-like projection, indicating increasing detachment from the sperm head. In the dogs treated with GnRH agonist there was clear evidence of cessation of normal spermatogenesis in most of the seminiferous tubules. Changes in the histology of the head of the epididymis were similar to (but more profound than) those found in the dogs treated with MPA. Seminal changes were demonstrated in ejaculates collected during the latter stages of the treatment period.