Regulation of Electrical Activity in the Myometrium of the Pregnant Ewe

Abstract

Periodic contractions have been recorded from the uterus of many species during pregnancy (Taverne et al. 1979; Germain et al. 1982; Bell 1983; Demianczuk et al. 1984). In ewes, two contractions per hour occur after day 60 of gestation, and when pairs of electromyographical (EMG) electrodes are placed at several locations on the uterus, bursts of EMG activity can be recorded that occur approximately synchronously at the various sites (Harding et al. 1982). Since each burst of EMG activity across the uterus is associated with a small rise in intrauterine pressure (IUP), measured via an intra-amniotic catheter, it seems reasonable to assume that activity is generalized throughout the uterus during a burst. In this paper we will consider the generation of the bursts of EMG activity rather than their propagation throughout the organ. We will address the question as to whether the bursts are an intrinsic property of the muscle or whether activity is initiated by the periodic release of spasmogen.