CYCLOOXYGENASE-2 UNLIKE CYCLOOXYGENASE-1 IS HIGHLY EXPRESSED IN-OVINEEMBRYOS DURING THE IMPLANTATION PERIOD

In this study we investigated expression of the two isoforms of the pr ostaglandin-forming enzyme, cyclooxygenase-1 (Cox-1) and cyclooxygenas e-2 (Cox-2), in sheep embryos. Using Western blot and immunohistochemi cal analyses, we demonstrated that Cox-2 was highly expressed in embry os from Day 8 to Day 17 of development whereas Cox-1 was undetectable during this time. The expression of Cox-2 was developmentally regulate d. 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, corre sponding to a 50000-fold increase in the whole embryo. The expression of Cox-2 declined after Day 16 to become undetectable by Day 25 of pre gnancy. Cox-2 was localized in the trophoblastic cells and was not det ected in the inner cell mass. The [H-3]arachidonic acid metabolites sy nthesized 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. Cyclooxy genase products were 6-keto-prostaglandin (PGF)(1 alpha) 18.2% (+/- 4. 2), thromboxane-B, 22.51% (+/- 15.9), PGF(2 alpha) 21% (+/- 11), PGE(2 ) 14.5% (+/- 7.4), and PGD(2) 2.7% (+/- 2.6). Taken together, these re sults suggest an important role for the Cox-2-dependent cyclooxygenase metabolites during embryo development.