Duration of pseudopregnancy induced by sterile mating in rats treated with prostaglandins

Pseudopregnancy, induced in rats by sterile mating, lasted 13 days (median). The subcutaneous administration of PGF_2α produced a significant shortening of this period (< 10 days), and PG administration on day 6 appears most suitable for assay purposes. A dose-response curve for PGF_2α administered twice on day 6 is presented; the ED₅₀ for termination of pseudopregnancy was estimated at 577 mcg/injection with 95% confidence limits at 463 and 723 mcg. PGE₂ is also effective; 40% of rats returned to estrus at a dose of 1000 mcg twice on day 6, suggesting a potency of about PGF_2α.