Myometrial electrical activity throughout the entire course of pregnancy in the ewe

Bipolar electrodes were implanted into the myometrium of three cycling ewes. Natural mating took place 35, 47 and 91 days after surgery, and all three animals became pregnant. Two of them were slaughtered 18 and 40 days after mating, the third delivered twin lambs 144 days after mating. The uterine electrical activity was recorded during pregnancy and parturition. From the 3rd until the 27th day after mating the uterus appeared to be quiescent. From the 5th wk of pregnancy until induction of parturition on day 141, electrical activity was observed to occur in episodes of 5--10 min, with a frequency of 1--3 per 2 h. The episodes are separated by periods of inactivity. The amplitudes of the electrical discharges increased gradually during pregnancy, although the plasma progesterone levels increased also. It is concluded that (1) the implanted electrodes did not interfere with normal reproductive processes such as conception, maternal recognition of pregnancy, implantation and fetal development: (2) a distinct pattern of electrical activity can be detected as early as the 5th wk of pregnancy.