Effect of intrauterine estriol on reproductive function in the rabbit

The effect of intrauterine estriol on spontaneous ovulation, ovum fertilization, blastocyst development, and blastocyst implantation in rabbits has been investigated. Estriolreleasing intrauterine capsules constructed of biocompatible polymer were implanted in one uterine horn of adult New Zealand White female rabbits, while placebo-containing capsules were implanted into the contralateral horn. The animals were artificially inseminated and ovulated or mated to fertile bucks. The does were killed and their reproductive tracts were examined 54 hours, 6 days, and 10 days after ovulation-inducing injection or after coitus. The results indicate that intrauterine estriol released at a steady state rate of 1.25 mug/day effectively inhibits blastocyst development and implantation. This contraceptive effect was clearly local, since implantations in the contralateral,placebo-bearing horn were not inhibited. Furthermore, the same dose of estriol, when released systemically from a subcutaneously placed capsule, had no effect on implantation. Intrauterine estriol appeared also to have no effect on spontaneous ovulation or ovum fertilization.