ROLE OF NITRIC-OXIDE ON OXYTOCIN-EVOKED CONTRACTIONS AND PROSTAGLANDIN SYNTHESIS IN ISOLATED PREGNANT RAT UTERUS

Uterine contractions elicited by oxytocin (OT), possibly linked with u terus prostaglandin (PG) release, are involved in the final pathway of labor. It is known that nitric oxide (NO) may contribute to the maint enance of uterine contractile quiescence during gestation. Therefore i n this study the effect of the inhibition of NO synthase (NOS), with N -monomethyl L-arginine (L-NMMA), on the ability of OT to stimulate ute rine contractions and PG synthesis was investigated in isolated rat ut erus at days 13 and 21 of pregnancy. L-NMMA did not modify the frequen cy and the force of contractions elicited by OT at day 13. On day 21 t he frequency of contractions evoked by OT were better sustained in the presence of L-NMMA. PGs were not affected by OT on day 13. OT stimula ted PGF(2 alpha) on day 21 when NOS had been inhibited with L-NMMA, bu t not in the absence of L-NMMA. NOS activity was stimulated by OT at d ay 21 of gestation. In summary these findings indicate that near term NO can regulate OT PGF(2 alpha) induced contractions and PG synthesis in isolated pregnant rat uterus.