Correlation of increased concentration of ovine endometrial cyclooxygenase2 with the increase in PGE(2) and PGD(2) in the late luteal phase

Ovine endometrium showed transient expression of high concentrations of the inducible isoform of cyclooxygenase, cyclooxygenase 2 (COX-2), whereas the constitutive isoform, cyclooxygenase 1 (COX-1), was expressed at much lowe r concentrations and did not change, in this study, the pattern of prostagl andin synthesis in endometrial luminal cells was investigated in relation t o their COX-2 content. Endometrial cells from cyclic or pregnant ewes at da ys 9, 12, 14 and 16 were isolated and analysed for the presence of COX-1 an d COX-2 proteins using western blot analysis. Freshly isolated cells were i ncubated with 0.5 mu Ci [H-3]arachidonic acid ml(-1). Radioactive cyclooxyg enase metabolites were analysed by reverse-phase HPLC. Luminal cells produc ed mainly PGF(2 alpha), PGE(2), PGD(2) and 13,14-dihydro-15-keto PGF(2 alph a) and to a lesser extent 6-keto PGF(1 alpha), thromboxane B2 and 13,14-dih ydro-15-keto PGE,. The production of PGE, and PGD, was proportional to the cellular concentration of COX-2. PGE, and PGD, release was low on day 9 whe n COX-2 was not expressed, whereas high concentrations of PGE, and PGD, wer e synthesized on days 12-14 when COX-2 was highly expressed, reaching 100 n g mu g(-1) cellular protein. Ln contrast, the basal production of PGF(2 alp ha) did not appear to be related to COX-2 concentration and was greatest on day 16. Moreover, the release of PGF(2 alpha) was maintained at steady sta te values between days 9 and 14 by the production of 13,14-dihydro-15-keto PGF(2 alpha). Although PGF(2 alpha) output was lower at day 16 of pregnancy compared with the oestrous cycle, no difference was observed in the patter n of prostaglandin synthesis between pregnant and non-pregnant ewes.