Fertility control in male rats by continuous release of microquantities of cyproterone acetate from subcutaneous silastic capsules

Abstract

The effects of continuous release of microquantities of the anti-androgen, cyproterone acetate, from implanted Silastic capsules on fertility in male rats are reported. Two capsules, each containing approximately 20 mg of cyproterone acetate, were implanted subcutaneously in each adult male rat. The average cumulative release rate was about 232 μg/day. Rats were autopsied 2, 4 and 6 months after implantation and 15 and 30 days following removal of the capsules thereafter. The weights of the testes and accessory glands and their secretory activity were not altered. However, the content and concentration of sialic acid in the epididymis decreased markedly at 4 months and gradually increased to control levels by 15 days after removal of capsules. Epididymal sperm were immotile at 4 and 6 months after implantation and remained so 15 days after removal of the capsules. Capsule-bearing rats mated normally. Ejaculated sperm were non-motile at 4 and 6 months and were apparently non-viable since none of the mated females had implantation sites or gave birth to litters. A gradual recovery of fertility occurred by 30 days following removal of capsules. These results show that continuous release of cyproterone acetate at doses too low to inhibit testicular and androgenic function altered the internal milieu of the epididymis resulting in loss of motility and viability of sperm. These results highlight the use of Silastic capsules filled with cyproterone acetate for causing reversible sterility in male rats without loss of mating behavior.