Uterine EMG activity in the non-pregnant sow during estrous cycle

Background: Uterine myoactivity is crucial for successful reproductive performance of the sow. Spontaneous contractions of the uterus are strictly controlled and coordinated. Uterine electromyographic (EMG) activity undergoes hormonal regulation with rapid and long-term effects. What is more, interstitial Cajal-like Cells (ICLC) appear essential for smooth muscle contractility in the reproductive tract where they are suspected to be playing a major role in generating, coordinating, modulating and synchronizing slow triggering waves. The aim of this study was to investigate the myoelectrical activity of sow's uterus during estrus cycle. Results: Study was conducted on 10 Polish Landrace sows. Propagation mechanisms and their connection with the uterine EMG activity were considered in correlation with expression of c-kit progesterone and oxytocin receptors of the non-pregnant sow. ICLC were labeled with antibody directed against c-kit receptor and visualized by confocal microscopy and scanning cytometer for positive cells percentage assessment. EMG signal was recorded directly from the myometrium with telemetry transmitters and electrodes located in different topographic regions of reproductive tracts. The stages of estrus cycle were determined by monitoring levels of luteinizing hormone, progesterone and estrogen with radioimmunoassays. Significant differences of the EMG signal parameters between diestrus and estrus and the correlations with density of labelled receptors were demonstrated. Moreover, the electrophysiological studies indicated that ICLC in the myometrium in the tip of uterine horn may participate in the regulation of slow waves duration and frequency. Conclusions: The pattern of EMG signal propagation in the wall of the non-pregnant porcine uterus occurs in an orderly, bidirectional fashion and at distinctive speed, with no differences between diestrus and estrus.