Evidence for a possible role of prostaglandins in implantation in rats.

Indomethacin (IM), a potent inhibitor of prostaglandin synthetase, significantly inhibited implantation in rats when administered at a single subcutaneous dose of 15 mg/kg on day 2 or 3 of pregnancy or at a dose of 800 micrograms administered intraluminally in the uterus on day 4 of pregnancy. Indomethacin, administered subcutaneously at a dose of 6 mg/kg on day 3 or 4 of pregnancy and intraluminally at a dose of 800 micrograms/rat on day 4 of pregnancy, also significantly reduced uterine prostaglandin levels. It is suggested that a certain level of uterine prostaglandins is essential for normal implantation and that indomethacin inhibits implantation by reducing uterine prostaglandin levels.