ABSTRACT
The Obligatory Role of the Chorionic Membranes in the Synthesis of Myometrial cGMP during Pregnancyand Its Inhibition by Maternal and Fetal Plasma The mechanism of uterine quiescence during pregnancy and initiation of labor is unknown. In previousreport, we demonstrated myometrial cGMP rises dramatically during pregnancy and then declines just priorto the onset of labor. Further, pregnancy decrease myometrial soluble guanylate cyclase activity whileenhancing particulate activity. Theses findings suggest a natriureitc peptide(NP) is responsible for theincrease in cGMP. This study was undertaken to evaluate the source of that NP. We incubatedmyometrium from term guinea pigs in oxygenated buffer in the absence/presence of either amnionicmembranes(AM, 400mg), chorionic membrane(CM, 400mg), fetal guinea pig plasma(FP, 1ml), maternalguinea pig plasama(MP, 1ml), or a combination. After incubation, cGMP(mol/mg portein) was measuredby radioimmuno assay. Both AM and CM(CM>AM, significantly) increased myometrial cGMP. Thestimulation of myometrial cGMP by the CM has a significant linear relationship between fetal weight andthe greatest cGMP increase occurred between 51~60 days after which it showed a trend to decrease. BothFP and MP decrease myometrial cGMP and inhibition of cGMP by MP increase significantly withadvancing gestational age.Our date indicate that myometrial cGMP is stimulated by a compound produced by the CM and the actionof this compound is inhibited by a substance produced by the mother and fetus at the end of a normalpregnancy.