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Prostaglandin E2(PGE2) and progesterone appear to be critical mediators of cumulus expansion and the resumption of oocyte meiosis. The aim of this study was to identify the types of prostaglandin E synthase (PTGES) expressed in the bovine cumulus–oocyte complex (COC), to characterize their temporal expression during the periconceptional interval using anin vitromodel of maturation (IVM) and fertilization (IVF), and to compare their expression with the level of steroidogenic gene expression. Real-time RT-PCR analysis revealed that enzymes related to the PGE2biosynthesis pathway were mainly expressed during IVM. Transcripts encoding PTGES1–3 were detected in bovine COCs. Only the expression of PTGES1 significantly increased during IVM whereas that of PTGES2 and PTGES3 remained unchanged. The induction of PTGES1 expression paralleled the induction of prostaglandin G/H synthase-2 (PTGS2) expression and the amounts of PGE2secreted by maturing COCs. Concomitantly, cholesterol side chain cleavage cytochrome P450 expression was significantly upregulated in maturing COCs and the high level of expression persisted in fertilized COCs. The expression of the StAR protein remained constant during IVM and then decreased significantly during IVF. Expression of the progesterone catabolic-related enzyme, 20α-hydroxysteroid dehydrogenase significantly decreased throughout the periconceptional interval. This was associated with a rising level of progesterone released by COCs in the culture media. In conclusion, our results suggest that the periconceptional differentiation of the bovine COC includes the transient induction of PGE2biosynthetic activity via the PTGS2/PTGES1 pathway during the maturation period and the increasing ability to produce progesterone from the immature to the fertilized stages.

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 lower concentrations and did not change. In this study, the pattern of prostaglandin synthesis in endometrial luminal cells was investigated in relation to their COX-2 content. Endometrial cells from cyclic or pregnant ewes at days 9, 12, 14 and 16 were isolated and analysed for the presence of COX-1 and COX-2 proteins using western blot analysis. Freshly isolated cells were incubated with 0.5 microCi [3H]arachidonic acid ml-1. Radioactive cyclooxygenase metabolites were analysed by reverse-phase HPLC. Luminal cells produced mainly PGF2 alpha, PGE2, PGD2 and 13,14-dihydro-15-keto PGF2 alpha and to a lesser extent 6-keto PGF1 alpha, thromboxane B2 and 13,14-dihydro-15-keto PGE2. The production of PGE2 and PGD2 was proportional to the cellular concentration of COX-2. PGE2 and PGD2 release was low on day 9 when COX-2 was not expressed, whereas high concentrations of PGE2 and PGD2 were synthesized on days 12-14 when COX-2 was highly expressed, reaching 100 ng microgram-1 cellular protein. In contrast, the basal production of PGF2 alpha did not appear to be related to COX-2 concentration and was greatest on day 16. Moreover, the release of PGF2 alpha was maintained at steady state values between days 9 and 14 by the production of 13,14-dihydro-15-keto PGF2 alpha. Although PGF2 alpha output was lower at day 16 of pregnancy compared with the oestrous cycle, no difference was observed in the pattern of prostaglandin synthesis between pregnant and non-pregnant ewes.