Cellular mechanisms involved during oxytocin-induced prostaglandin F-2 alpha production in endometrial epithelial cells in vitro: Role of cyclooxygenase-2

PGs are important regulators of reproductive processes. At the time of luteolysis in vivo, PGF(2 alpha) is produced by endometrial cells, in response to oxytocin (OT). The mechanism by which OT induces the release of PGF(2 alpha) remains to be defined. We have used 13 different cultures of bovine epithelial endometrial cells to study the effect of OT on the regulation of PGF(2 alpha) and to identify the possible involvement of cyclooxygenases (COXs). OT induced a dose-dependent increase of both inositol phosphates (IPs) and [Ca2+](i) concentration in epithelial cells labeled with [H-3]-myoinositol or loaded with fura-2 (using a fluorescent microscope imaging system), respectively. OT induced a dose-dependent, increase of both PGF(2 alpha) production and COX-2 gene expression las demonstrated by RT-PCR and Northern blots). PGF(2 alpha) production was increased from 13.3 +/- 2.0 to 166.8 +/- 22.5 ng/ml (P < 0.0001). On the other hand, COX-2/beta-actin mRNA gene expression (as determined by densitometric analysis) was increased 5.1 +/- 0.7-fold (P < 0.001) with OT (10(-7) M) treatment, compared with control. addition of indomethacin (1 mu M) and a specific COX-2 inhibitor (NS-398, 1 mu M) blocked the OT-induced PGF(2 alpha) production. COX-1 and phospholipase A(2) mRNA were expressed at steady-state levels, but no effect of OT was detected on their regulation. Combined to OT, 10 mu g/ml of recombinant ovine interferon-tau (roIFN-tau) was able to decrease significantly (P < 0.0001) the dose-dependent increase of PGF(2 alpha) production. Furthermore, partial bovine COX-1 (777 pb) and COX-2 (449 bp) cDNAs were cloned and sequenced. An homology of 83% and 97% was found in relation with rat and sheep, for COX-I, respectively. COX-2 was found to bear 84%, 86%, and 87% of homology in relation to rat, guinea pig. and human, respectively. Collectively, these results demonstrate, for the first time, that COX-2 is involved in the mechanism by which OT regulates PGF(2 alpha) production in the endometrium.