Cyclooxygenase-2 Unlike Cyclooxygenase-1 is Highly Expressed in Ovine Embryos during the Implantation Period1

In this study we investigated expression of the two isoforms of the prostaglandin-forming enzyme, cyclooxygenase-1 (Cox-1) and cyclooxygenase-2 (Cox-2), in sheep embryos. Using Western blot and immunohistochemical analyses, we demonstrated that Cox-2 was highly expressed in embryos from Day 8 to Day 17 of development whereas Cox-1 was undetectable during this time. The expression of Cox-2 was developmentally regulated. It was maximal between Days 14 and 16. There was a 30-fold increase in Cox-2 content per protein extract between Day 10 and Day 14, corresponding to a 50,000-fold increase in the whole embryo. The expression of Cox-2 declined after Day 16 to become undetectable by Day 25 of pregnancy. Cox-2 was localized in the trophoblastic cells and was not detected in the inner cell mass. The [3H]arachidonic acid metabolites synthesized by Cox-2-rich conceptuses were analyzed by HPLC after short-term embryo culture. Day 14 conceptuses released mainly cyclooxygenase metabolites and to a lesser extent lipoxygenase derivatives. Cyclooxygenase products were 6-keto-prostaglandin (PGF)1alpha 18.2% (+/- 4.2), thromboxane-B2 22.51% (+/- 15.9), PGF2alpha 21% (+/- 11), PGE2 14.5% (+/- 7.4), and PGD2 2.7% (+/- 2.6). Taken together, these results suggest an important role for the Cox-2-dependent cyclooxygenase metabolites during embryo development.