An electromyographic study of uterine activity during normal and progestogen-regulated estrus in the ewe

Myometrial electrography was performed by means of chronically implanted electrodes in the base, the middle and the tubal end of both the uterine horns of six Serres ewes at normal and progestogen-regulated estrus. During the first 24 h of normal estrus, myometrial electrical activity was characterized by intermittent spike bursts (Pattern I activity), occurring at about the same frequency in the three sites of both horns (middle of the right horn: 44.13+/-6.07/30 min). This pattern was then gradually transformed so that 36 h after the beginning of estrus, there was mostly only episodic activity consisting of 18.22+/-3.44 bursts, lasting 6.50+/-2.42 mins, and recurring at 30.51+/-16.24 min intervals simultaneously in both horns (Pattern II activity). During Patterns I and II, the respective ratios of descendingly to ascendingly propagated bursts were 2.65 and 0.78. Pattern I activity also occurred during the first 24 h of progestogen-regulated estrus, but the frequency of the bursts of spikes although occurring in the tubal ends of both horns at about the same rate as in Pattern I at normal estrus, gradually decreased towards the uterine body, (tubal end: 44.34+/-4.28, middle: 40.14+/-5.42, and base: 33.22+/-4.82/30 min). Then Pattern I activity was transformed into a miscellaneous pattern instead of into Pattern II. In the progestogen-regulated estrus, the ratio of the descending to the ascending propagations of spikes during Pattern I activity rose to 5.11.