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

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Abstract

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.

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About the authors

S. A. Rutkevich

Belarusian State University; Belarusian State Medical University

Author for correspondence.
Email: rutkevitch@inbox.ru
Belarus, Minsk; Minsk

P. G. Pihul

Belarusian State University

Email: rutkevitch@inbox.ru
Belarus, Minsk

Yu. D. Panimatska

Belarusian State University

Email: rutkevitch@inbox.ru
Belarus, Minsk

V. B. Kazakevich

Belarusian State University; Belarusian State Medical University

Email: rutkevitch@inbox.ru
Belarus, Minsk; Minsk

I. A. Veres

Belarusian State Medical University

Email: rutkevitch@inbox.ru
Belarus, Minsk

A. V. Sidorov

Belarusian State University

Email: rutkevitch@inbox.ru
Belarus, Minsk

A. G. Chumak

Belarusian State University

Email: rutkevitch@inbox.ru
Belarus, Minsk

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2. Fig. 1. Cytological preparations of rat vaginal swabs at different stages of the estrous cycle: (a) - diestrus, (b) - proestrus, (c) - estrus, (d) - metestrus; 1 - leukocytes, 2 - mucus, 3 - epithelial cells with nuclei, 4 - keratinised eggless epithelial scales, 5 - bacterial contamination. Image on the left - ×10 objective, on the right - ×40 objective. The calibration line is 100 µm.

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3. Fig. 2. Electrical activity of the rat uterus at different stages of the estrous cycle: (a) - diestrus, (b) - proestrus, (c) - estrus, (d) - metestrus. Part (d) shows the burst and pause phases of the electrical activity period (cycle period). Calibration lines: in amplitude - 100 μV, in time - 30 s.

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4. Fig. 3. Phase duration of the periods of myometrial electrical activity at different stages of the estrous cycle. The value of the index (numbers above the bar) and the number of analysed periods of electrical activity (n) are indicated. Data are in the form of median ± interquartile range. The F-criterion value and significance level (p) of the Kruskal-Wallis ANOVA (one-factor analysis of variance) for the whole data series are given. The Mann-Whitney z-score and significance level (p) for statistically significant differences (*) between pairs of data are given.

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5. Fig. 4. Filling factors of the periods of myometrial electrical activity at different stages of the estrous cycle: DiE - diestrus, ProE - proestrus, Estrus - estrus, MetE - metestrus. Other designations are the same as in Fig. 3.

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6. Fig. 5. Amplitude characteristics of myometrial electrical activity at different stages of the estrous cycle: (a) - maximum amplitude, (b) - average amplitude; DiE - diestrus, ProE - proestrus, Estrus - estrus, MetE - metestrus. The value of the index (numbers above the bar) and the number of animals studied (n) are indicated. Data are in the form of mean ± error of the mean. The F-criterion and significance level (p) of one-way ANOVA for the whole data series are given. For statistically significant differences (*) between pairs of data, Student's t-criterion and significance level (p) are given.

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7. Fig. 6. Frequency characteristics of myometrial electrical activity at different stages of the estrous cycle: (a) - dominant frequency, (b) - average frequency; DiE - diestrus, ProE - proestrus, Estrus - estrus, MetE - metestrus. Index value (numbers above the bar) and number of animals studied (n) are indicated. Data as median ± interquartile range. The F-criterion value and significance level (p) of the Kruskal-Wallis ANOVA (one-factor analysis of variance) for the whole data series are given. The Mann-Whitney z-score and significance level (p) for statistically significant differences (*) between pairs of data are given.

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