Production of Prostaglandin F2α and E2 in Explants of Intrauterine Tissues of Guinea Pigs during Late Pregnancy and Labor

Prostaglandin production in amnion and decidua is considered important for human parturition. We investigated in pregnant guinea pigs, a species similar to women in regard to the endocrinology of pregnancy, whether the production rates of PGE₂ and PGF_2α in various intrauterine tissues are compatible with a role in parturition. Net production rates were measured at 45, 55 and 65 days of gestation and during labor in amnion, chorion, myo-endometrium, the outer layer of the myometrium, the site of placental implantation, and placenta. Net production rates in amnion increased between 45 days and labor (30-fold for PGE₂ and 8-fold for PGF_2α, P < 0.0001). During labor, the production rates in amnion of PGE₂ (P = 0.006) and PGF_2α (P = 0.019) were higher than at 45, 55, and 65 days of gestation. In myo-endometrium, the production rates of PGF_2α were higher at 65 days of gestation than at 55 days and during labor (P = 0.046). Addition of arachidonic acid (10⁻⁵ M) increased production of PGE₂ and/or PGF_2α in all tissues (P < 0.05) except placenta. In amnion, the response to arachidonic acid increased with advancing gestation. This suggests that 1) PGE₂ and PGF_2α produced by amnion have a potential role in the initiation and maintenance of labor, 2) PGF_2α produced by myo-endometrium has a potential role in the initiation of labor, 3) cyclooxygenase(s) are not rate-limiting except in placenta, and 4) the expression of cycloxygenase in amnion increases with advancing gestation.