Modulatory effects of neurohypophysary origin hormones on placental hormone secretion at term.

Oxytocin (OT) and arginine-vasopressin (AVP) are two major neurohypophysary nonapeptides that have impor-tant roles during pregnancy and labor. Using the expiant model at term, we have examined the effect of physiologic concentrations of both nonapeptides on placental hormone secretion. We found that OT had a dose-dependent inhibitory effect on P (2-3-fold.P<0.05) and hCG (2-fold,P<0.05) while increasing E(2) secretion (150-180%,P<0.05) into the media. The effect of OT on P secretion was receptor-dependent since it was abolished by addition of CAP-450 into the media. AVP increased E(2) secretion up to 2-fold. <0.05) while not having a consistent effect on P secretion. In conclusion, OT and to a lesser degree AVP, have significant modulatory effects on placental hormone secretion. Whether the resulting locally increased E(2)/P secretion ratio favors progression of labor remains to be shown.