Electrical and mechanical activity of the cervix in the ewe during pregnancy and parturition.

Abstract

Summary. Myoelectrical and mechanical activities of the uterine cervix and horns of ewes fitted with electrodes and strain gauges were measured from the 30th day before until the 3rd day after parturition. During pregnancy, cervical electromyograms presented regular episodes of strong activity of a mean duration of 7 min, termed regular spiking activity, occurring at about 50-min intervals. Between two episodes, isolated or low frequency spikes occurred randomly and constituted the irregular spiking activity. The alternation of irregular and regular spiking activities was called the myoelectrical complex of the cervix. Clear relationships were noticed between electrical and mechanical events. On the pregnant uterine horn (singleton pregnancy) or on both horns (twin pregnancy), a myoelectrical complex pattern similar to that of the cervix was recorded. Regular spiking activity on the cervix and pregnant horn(s) occurred mainly simultaneously. No significant evolution of the myoelectrical complex pattern was noted throughout the last month of pregnancy until 2\p=n-\3days before parturition. The activity pattern was then modified according to three characteristic phases: (1) a phase of relative inhibition of the cervix and pregnant horn(s) 48 h before lambing and lasting about 17 h; (2) a phase of increasing activity occurring thereafter over the whole genital tract with an average duration of 31 h; and (3) a phase of continuous activity of the cervix and uterus for 0\m=.\4\p=n-\3\m=.\8h which accomplished the expulsion of the lamb. It is concluded that during the last month of pregnancy the cervix is active and that its activity arises from a basic ultradian rhythm involving the entire genital tract. Furthermore, although our results do not offer an explanation for the preparturient increase of cervical compliance described by others, they definitely excluded cervical muscular inhibition during the last 24 h of pregnancy and at the time of cervical dilatation.