Long-term regulation of male fertility by norethisterone enanthate 'epididymal' implants: effect on libido and fertility of rabbits.

Bilateral insertion of silastic capsules releasing 38-44 micrograms norethisterone enanthate/24 h into the epididymal fat-pads was found to induce complete azoospermia leading to infertility in adult male rabbits 8 weeks after insertion of the progestin implants. The treatment did not exert any inhibitory effects on the libido and sexual behaviour of the animals as judged by objective parameters of mating. Further, the failure of the hormone-releasing implants was not found to exert any adverse effects on the embryos and pregnancy as indicated by the delivery of normal pups to females mated with implant-bearing males 3 weeks after the insertion of 'epididymal' implants.