[Effect of oxytocin administration on prostaglandin concentrations in uterine and placental tissues of pregnant rabbit (author's transl)].

To clarify the mechanism of labor onset, the effect of exogenous oxytocin (OT) on tissue prostaglandin (PG) formation was studied in vivo. Changes of PG concentrations of the uterine venous plasma, myometrium, fetal and maternal cotyledons of placenta, and parietal decidua of late pregnant rabbits were evaluated between just before and 10 minutes after administration of 10 IU of OT. PGE1, PGE2, and PGF2 alpha were extracted from each tissue by Inagawa's method and measured by radioimmunoassay. Concentrations of PGE1 (344-1,280 ng/g wet weight) and PGE2 (656-3,000 ng/g wet weight) of the fetal cotyledon were 2-30 times higher than those of other tissues regardless of OT administration. Differences in PG concentrations between before and after OT administration were compared. The results were: 1) Changes of PGs in the plasma, fetal cotyledon, and parietal decidua showed no definite tendency after OT administration. 2) In the myometrium, all measured PG decreased after OT administration, suggesting that tissue PGs are not concerned with myometrial contraction when induced by exogenous OT. 3) In the maternal cotyledon of the placenta, PGs increased after OT administration, suggesting that the maternal cotyledon is the only site having close relationship between OT administration and PGs formation in vivo.