[In vitro study of the motor activity of two muscle layers in the rabbit oviduct]

Electrical and mechanical activities in the circular layer in the longitudinal peritoneal muscle were recorded in vitro in the oviducts of untreated and estrogen-treated ovariectomized rabbits. The duration and frequency of the bursts were not significantly changed in either muscle layer by the hormonal treatment. Estradiol increased the propagation of electrical activity in the isthmus and the amplitude of the contractions as well as the synchronization between the mechanical and electrical activities in the two muscle layers. Recordings of both electrical and mechanical activities were necessary to estimate the effects of the estrogen on the muscular layers. Removal of the longitudinal fiber bundles modifying the pattern of electrical and mechanical activities in the circular layer of the isthmus only increased the frequency of circular bursts and the frequency and amplitude of intraluminal pressure changes in both groups of animals. It is supposed that removal of the longitudinal fiber bundles could have damaged the inhibitory isthmic innervation of the circular layer. The EMG activity of the longitudinal layer was generally independent from that of the circular layer in the oviducts of estrogen-treated rabbits. In 24 p. 100 of records which showed a synchronization of the electrical and mechanical activities of both muscle layers in the isthmus, the times between the contractions of the two muscle layers varied from 0.1 to 3.2 sec, suggesting that they were mechanically coupled.