Experiments were performed to determine if the time- and hormone-dependencies of the decidual cell reaction in rats were maintained when prostaglandins (PGs) were infused into the uterine lumen from Alzet osmotic mini-pumps. Ovariectomized rats treated with estradiol and progesterone were used. In the infusion experiments, to reduce uterine PG production during decidualization, the rats received a single s.c. injection of 2 mg indomethacin before pump insertion, and the infusion vehicle contained 0.5 mM indomethacin. Decidualization was assessed by uterine weights 5 days after pump insertion or intrauterine injection of 100 microliter of sesame oil. Temporal changes in sensitization were investigated by treating the rats with estradiol and progesterone to achieve the equivalents of Day 4, 5 or 6 of pseudopregnancy. Sensitization was greatest on Day 5 as indicated by decidualization in response to intrauterine sesame oil. Hormone-dependency was investigated by administering varying amounts of estradiol to rats for the 2 days preceding and on the day of uterine treatment (totals of 0, 0.4 and 3 micrograms estradiol); thereafter, until sacrifice, all rats received the same combination of estradiol and progesterone. Uterine sensitization was greatest in rats receiving the intermediate dose of estradiol. The ability of PGs to produce decidualization when infused into nonsensitized uteri ranged from having no effect (in rats receiving the high dose of estradiol) to producing almost as much decidualization (in low estradiol animals) as in the maximally sensitized animals. In general, PGE2 was more effective than PGF2 alpha.(ABSTRACT TRUNCATED AT 250 WORDS)