Inhibition of fetal membrane prostaglandin production by prolactin: relative importance in the initiation of labor.

Production of a biologically active prolactin by human decidual tissue and its influence on the permeability of amniochorion to water suggests a functional relationship between the polypeptide and fetal membrane metabolism. Under in vitro circumstances, we used ovine prolactin and the Ussing chamber technique to determine the role of prolactin in prostaglandin E2 production by human fetal membrane. Fresh reflected membranes obtained from elective cesarean sections were exposed to ovine prolactin (10 micrograms/ml). Aliquots of incubation media were sampled at 0, 30, 60, 120, and 240 minutes, quick-frozen, and later assayed for prostaglandin E2. Multifactorial analysis of variance revealed that ovine prolactin significantly reduced prostaglandin E2 production (f = 13.42, p less than 0.005). Prostaglandin E2 output was greatest by amnion (3581 +/- 596 pg/ml/gm declining to 1819 +/- 452 pg/ml/gm during 4 hours). Other combinations of fetal membranes including amnion-chorion-decidua produced only 12% to 15% prostaglandin E2 per gram compared with that produced by amnion alone. Those membranes similarly responded to prolactin with a reduction in prostaglandin E2 output of 34% to 59%. Correlation analysis identified a significant relationship between prostaglandin E2 production and time (r = 0.298; p less than 0.001), which was abolished by ovine prolactin (r = 0.115, p greater than 0.10). This model illustrates that ovine prolactin modifies the production of prostaglandin by fetal membranes in vitro. By analogy, endogenous prolactin by human decidual tissue might also inhibit the elaboration of prostaglandin E2 from its precursors residing within the fetal membranes.