Inhibition of fertilization in the rabbit long after injection of Depo-Provera.

Mature female rabbits were given subcutaneous injections of 20 or 50 mg Depo-Provera (Upjohn Company, Kalamazoo, MI) (medroxyprogesterone acetate). Ovulation by mating was inhibited for 40 to 65 days. Although ovulation could be induced by injection of human chorionic gonadotropin, fertilization of eggs failed in all females 15 to 83 days after treatment. When treated and untreated females were inseminated with a definite number of spermatozoa and given human chorionic gonadotropin, fertilized eggs and spermatozoa were found in the oviducts of untreated, but not in the treated, females. Although spermatozoa were found in the uterine horns of treated rabbits, the number was much lower than in the untreated females. It is concluded that long after injection of Depo-Provera, not only was ovulation inhibited, but also fertilization, due to the suppression of sperm transport in the female tracts. The effects of progestins on various aspects of animal reproduction are discussed, stressing the effectiveness and efficiency of their contraception.