Registration of myometrial activity using multiple site electromyography in cyclic mares

Abstract

A method for interpreting and analysing electromyographic (EMG) data of myometrial electrical activity was established. This method was used to study EMG activity in the uterus during the various stages of the oestrous cycle in mares. Recordings were analysed from four pairs of electrodes that were surgically implanted in the myometrium of four reproductively sound mares. The electrodes were placed at the tip, middle and base of the left horn and in the uterine body. Electrical activity was monitored by a polygraph. Data were transformed to a digitized form and statistically analysed. Myometrial electrical activity during oestrus and dioestrus was analysed for frequency (number of activity bursts per hour), duration (time elapsed from the start to the end of a burst) and intensity (peaks per minute). In addition, the degrees of synchronous activity among all of the monitored sites of the uterus were compared. The minimal amount of time of EMG recordings that allowed meaningful statistical analyses was determined to be 3.5 h during oestrus and 7 h during dioestrus. Variations in intensity of electrical activity were seen between the sites of implanted electrodes (P < 0.001). Electrical activity was highest in the middle of the horn and lowest in the uterine body. The frequency of activity bursts was the same during oestrus and dioestrus (4.35 ± 0.22 and 4.44 ± 0.20, respectively). The duration and intensity of uterine electrical activity depended on the stage of the oestrous cycle. The mean duration of uterine activity bursts during dioestrus was significantly (P < 0.005) shorter during oestrus (3.32 ± 0.18 min) than during dioestrus (5.7 ± 0.39 min). The intensity of bursts was higher during oestrus than during dioestrus (P < 0.005). In contrast, the total time of uterine activity was higher during dioestrus than during oestrus (P < 0.005). Synchronization of uterine electrical activity among different sites of the uterus was more marked during oestrus than during dioestrus (P < 0.005). It was suggested that a hormone-dependent mechanism for the regulation of cell communication is responsible for at least part of the changes of myometrial electrical activity that was observed at different stages of the oestrous cycle. It was concluded from the study that the method described for analysing EMG data allowed for an objective and repeatable interpretation of myometrial electrical activity.