Prevention of pregnancy in rabbits using vaginal application of prostaglandin f2alpha

Seventy-two rabbits were artificially inseminated at the time of ovulation induced by intravenous human chorionic gonadotropin. Twenty-four hours later vaginal suppositories containing graded amounts of prostaglandin F2alpha (PGF2alpha) (5 to 25 mg) were inserted into test rabbits in each group. A control group received plain vaginal suppositories. Ten days later the rabbits were killed and examined for numbers of corpora lutea and implantation sites. The results indicate that 5 to 15 mg of PGF2alpha had no effect or a minimal effect on the number of implantation sites, that 20 mg of PGF2alpha reduced the number of implantation sites, and that 25 mg of PGF2alpha was the most effective dose. Fifteen of twenty treated rabbits were not pregnant, despite the presence of ovarian corpora lutea. Four remaining rabbits were pregnant but had markedly reduced implantation sites (four, two, three, and two fetuses, respectively. PGF2alpha is known to increase tubal motility markedly. These data are consistent with such a mechanism's inhibiting pregnancy when used postcoitally in rabbits.