Oxytocin and Uterine Function in Pregnant and Parturient Rats

Abstract

Uterine contractile activity was monitored in pregnant and parturient rats by means of previously inserted intrauterine balloons before and during oxytocin infusions. Labor could be induced at term by an infusion of 4-hr duration (1 mU/min for 2 hr followed by 2 mU/min for 2 hr). The duration and outcome of oxytocin-induced labor were very similar to spontaneous labor, and the oxytocin-induced contractions could not be distinguished from spontaneous contractions. Labor could not be induced earlier than 4–6 hr before expected term, although uterine contractions were elicited by the oxytocin infusions several days before term. Recordings obtained simultaneously from two different locations of the same uterine horn showed that during parturition the activity of the whole horn was synchronous whereas before term both ends of the uterine horn contracted independently. Shortly before parturition and during labor, activity in the ovarian end seemed to predominate and the contractions appeared to be initiated here.