Evidence for an inverse relationship between cyclooxygenase and lipoxygenase pathways in the pregnant rabbit endometrium.

In the present investigation, experiments were undertaken to determine whether a relationship does exist between cyclooxygenase and 5-lipoxygenase pathways in rabbit endometrial cells on day 6 of pregnancy. Endometrial single-cell suspensions were incubated in RPM1-1640 for 1 h under a gas phase of 95% O2 + 5% CO2 at 37 degrees C for 1 h in the presence and absence of indomethacin, a known inhibitor of cyclooxygenase or nordihydroguaiaretic acid (NDGA), a preferential inhibitor of 5-lipoxygenase. Prostaglandins (PGF2 alpha, PGE2 and 6-keto-PGF1 alpha) and 5 (S)-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE) were measured in the media by radioimmunoassay. Indomethacin or NDGA at all concentrations used suppressed the release of PGs or 5-HETE, respectively. However, NDGA at the lowest dose (15 microM) stimulated, but at higher doses (30-60 microM) suppressed the release of PGs. On the other hand, indomethacin at both the concentrations (55 microM and 110 microM) used stimulated the release of 5-HETE. The results suggest the existence of an inverse relationship between the two pathways in the preimplantation rabbit endometrial cells.