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

Experiments were performed under urethane anesthesia on sexuallymature non-pregnant female rats (n =36). Pattern of electrical activity of the uterus in different phasesof the estrous cycle, determined by the vaginal cytology (stainingby Romanovsky dye), was studied. Electrohysterograms from the middle thirdof the left horn of the uterus were recorded using pressure bipolarelectrodes. Increased excitability and conductivity of the uterussmooth myocytes occur during the stages of proestrus, estrus and metestrus,and their suppression is observed in diestrus. The maximum amplitudeof motor potentials, compared to diestrus, was detected at the pro-(174 ± 17 µV) and metestrus (202 ± 20 µV) stages, while their meanfrequency 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 activityhad it maximum while rest period had it minimum [46 (40; 55) and42 (26; 84) s] at proestrus and estrus stages which is also reflectedin 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 were27 (22; 32) and 80 (58; 124) s, 0.27 (0.18; 0.34). It is assumedthat the highest excitability of the myometrium and its rhythmogenicareas during the metestrus stage, an increase in myometrium’s excitationconduction rate during proestrus and estrus, are due to an increase ofelectrical coupling between uterus smooth muscle cells.