Uterine Prolactin and Labor: Modulation by Human Chorionic Gonadotropin Affects Prostaglandin (PG) E2 and PGF2a Production

During term labor, high concentrations of prosta glandin E 2 (PGE 2 ), and to a lesser extent prosta glandin F 2a (PGF 2a ), accumulate in the amniotic fluid because of increased synthesis by the fetal mem branes lining the gestational sac. 1-4 Since PGE 2 and PGF 2a are potent uterotonic agents, prostanoid pro duction by gestational sac membranes appears to facilitate the labor process. 5-8 Furthermore, in con trast to the increased production of PGE 2 on the fetal or amniotic membrane surface during labor, a con comitant rise in PGE 2 production does not occur on the maternal or decidual surface adjacent to the myometrium. 9 However, PGF 2a production on the maternal side does increase with labor, 10 suggesting that modulations in gestational sac membrane PGE 2 and PGF 2a occur with labor. These observations agree with clinical findings of a rise in circulating metabolites of PGF 2a during labor but not those of PGE 2 . 11 In addition to prostanoids, the gestational sac pro duces human chorionic gonadotropin (hCG) in the placenta and chorion laeve, and high levels of prolac tin (PRL) are synthesized by the maternal decidua that is in close cellular contact with the chorion laeve. 12,13 With the initiation of labor, circulating PRL significantly decreases, followed by a rapid rise within 2 hours of parturition, and continues until 2 hours postpartum. 14 Furthermore, exposure of the gestational sac membranes to high PRL levels appear to down-regulate PGE 2