The effect of antiprogestin (RU 486) and prostaglandin biosynthesis inhibitor (naproxen) on uterine fluid prostaglandin F2 alpha concentrations.

In the present study the effect of the antiprogestin RU 486 and the prostaglandin biosynthesis inhibitor, naproxen, on uterine fluid concentration of prostaglandin F2 alpha (PGF2 alpha) was investigated. RU 486, 200 mg, was administered two days after the luteinizing hormone (LH) surge and naproxen, 500 mg, was given every 12th hour five times starting 4 days after the LH surge. Uterine fluid was collected in the proliferative phase at ovulation and in the mid-luteal phase in a control and treatment cycle. The amount of PGF2 alpha was measured by gas chromatography-mass spectrometry. In the control cycle, the highest concentration of PGF2 alpha was found in the mid-luteal phase, and the lowest at the time of ovulation. Both RU 486 and naproxen reduced the PGF2 alpha concentration in uterine fluid considerably, or to 22-25% of that in the control cycle at the time of implantation. PGF2 alpha produced by the endometrium is believed to be of importance for the implantation of the blastocyst. Postovulatory treatment with RU 486 effectively prevents implantation, probably mainly by inhibiting the maturation of the endometrium during the secretory phase of the cycle. It is suggested that the inhibition of PGF2 alpha release through the uterine fluid caused by RU 486 may also be of importance.