Oxytocin gene expression in rat uterus.

The neurohypophyseal hormone oxytocin (OT) is the most potent uterotonic agent known and is used to induce labor. Yet, endogenous circulating OT appears not to participate in the induction of labor. As shown here, the finding of OT messenger RNA and peptide in the uterus suggests a solution for this paradox. During gestation, rat uterus OT messenger RNA increased more than 150-fold and, at term, exceeded hypothalamic OT messenger RNA by 70-fold. Thus, during parturition, OT may act primarily as a local mediator and not as a circulating hormone.