ROLE OF PROSTAGLANDIN PRODUCTION IN SPONTANEOUS AND OXYTOCIN-INDUCED UTERINE CONTRACTILE ACTIVITY IN INVITRO PREGNANT RAT UTERI

Uterine segments from pregnant rats were monitored in vitro for isometric contractile activity in Krebs-Ringer medium (95% O2-5% CO2; 37.degree. C). The medium was sampled periodically and assayed for PG[prostaglandin]E, PGF, and, in some cases, 13,14-dihydro-15-keto-PGF2.alpha. by RIA [radioimmunoassay]. Uteri from 21-day pregnant rats demonstrated more PGE and PGF release and greater integrated contractile force (ICF) than uteri from 18 day pregnant rats. Upon analysis of the more active uteri of 21 day pregnant rats, a significant positive correlation was found between PG production and either ICF (P < 0.05) or contractile frequency (P < 0.001) but not with amplitude or duration of contractions. Oxytocin (20 mU [units]) caused increased contractile activity in 18 day pregnant rat uteri, but no increase in PGE, PGF, or 13,14-dihydro-15-keto-PGF2.alpha. was observed. Indomethacin caused a decrease in PG production as well as a reduction in contractile activity. Indomethacin had little effect on the oxytocin-induced increase in contractile frequency at any time period measured or in ICF during the first 15 min of incubation, but ICF was reduced thereafter. However, ICF of these tissues was greater than tissues treated with indomethacin alone. While spontaneous contractions of the in vitro rat uterus are directly related to PG production, oxytocin-induced contractions do not depend upon increased PG production and, indeed, contractile activity can be induced by oxytocin vis a vis documented reductions in PG production. However, some threshold level of PG may be needed for maximal contractile response to oxytocin.