EFFECTS OF MEDROXYPROGESTERONE ACETATE OR GONADOTROPIN-RELEASING-HORMONE AGONIST ON SUPPRESSION OF SPERMATOGENESIS IN THE DOG (CANIS-FAMILIARIS)

Medroxyprogesterone acetate (MPA) was administered as a depot injectio n to two adult male dogs. One was injected with 75 mg as a depot injec tion once a month for 2 months and the other with 50 mg at 2-weekly in tervals for 1 month, followed by 100 mg at 2-weekly intervals for a fu rther 2 months. Two other male beagles were given gonadotrophin-releas ing hormone (GnRH) agonists (nafarelin derivative no. 49947 and nafare lin acetate) at a dose of 50 mug day-1 for either 22 or 23 days. The p rofiles of luteinizing hormone (LH) and testosterone were monitored be fore 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. I n contrast, in the dogs treated with GnRH agonist, LH and testosterone concentrations were suppressed for most of the treatment period. In t he MPA-treated animals, histological changes were seen mainly in the h ead of the epididymis, and in the acrosome region of the spermatozoa s till present in this region of the male reproductive tract. The acroso me, instead of being closely applied to the sperm head, was in contact only in the most anterior areas, with the remainder forming a fan-lik e projection, indicating increasing detachment from the sperm head. In the dogs treated with GnRH agonist there was clear evidence of cessat ion of normal spermatogenesis in most of the seminiferous tubules. Cha nges in the histology of the head of the epididymis were similar to (b ut more profound than) those found in the dogs treated with MPA. Semin al changes were demonstrated in ejaculates collected during the latter stages of the treatment period.