Electrical Activity of the Uterus in Rats at Different Stages of the Estrous Cycle

Experiments were performed under urethane anesthesia on sexually mature non-pregnant female rats (n = 36). Pattern of electrical activity of the uterus in different phases of the estrous cycle, determined by the vaginal cytology (staining by Romanovsky dye), was studied. Electrohysterograms from the middle third of the left horn of the uterus were recorded using pressure bipolar electrodes. Increased excitability and conductivity of the uterus smooth myocytes occur during the stages of proestrus, estrus and metestrus, and their suppression is observed in diestrus. The maximum amplitude of motor potentials, compared to diestrus, was detected at the pro- (174 ± 17 µV) and metestrus (202 ± 20 µV) stages, while their mean frequency was high at the metestrus [4.4 (4.0; 5.0) Hz] and estrus [4.0 (4.0; 5.0) Hz], exceeding those indicators for diestrus [86 ± 9 µV and 1.9 (1.3; 3.2) Hz] approximately twice. Burst phase duration [40 (32; 50) and 36 (28; 47) s] of uterus periodic electrical activity had it maximum while rest period had it minimum [46 (40; 55) and 42 (26; 84) s] at proestrus and estrus stages which is also reflected in the high values of duty cycle—0.46 (0.43; 0.50) and 0.45 (0.26; 0.63), respectively. Similar indicators for the diestrus stage were 27 (22; 32) and 80 (58; 124) s, 0.27 (0.18; 0.34). It is assumed that the highest excitability of the myometrium and its rhythmogenic areas during the metestrus stage, an increase in myometrium’s excitation conduction rate during proestrus and estrus, are due to an increase of electrical coupling between uterus smooth muscle cells.