CELLULAR MECHANISMS INVOLVED DURING OXYTOCIN-INDUCED PROSTAGLANDIN-F2-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 rele ase of PGF(2 alpha) remains to be defined. We have used 13 different c ultures of bovine epithelial endometrial cells to study the effect of OT on the regulation of PGF(2 alpha) and to identify the possible invo lvement of cyclooxygenases (COXs). OT induced a dose-dependent increas e of both inositol phosphates (IPs) and [Ca2+](i) concentration in epi thelial cells labeled with [H-3]-myoinositol or loaded with fura-2 (us ing 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 expres sion (as determined by densitometric analysis) was increased 5.1 +/- 0 .7-fold (P < 0.001) with OT (10(-7) M) treatment, compared with contro l. addition of indomethacin (1 mu M) and a specific COX-2 inhibitor (N S-398, 1 mu M) blocked the OT-induced PGF(2 alpha) production. COX-1 a nd phospholipase A(2) mRNA were expressed at steady-state levels, but no effect of OT was detected on their regulation. Combined to OT, 10 m u g/ml of recombinant ovine interferon-tau (roIFN-tau) was able to dec rease 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. CO X-2 was found to bear 84%, 86%, and 87% of homology in relation to rat , guinea pig. and human, respectively. Collectively, these results dem onstrate, for the first time, that COX-2 is involved in the mechanism by which OT regulates PGF(2 alpha) production in the endometrium.