Electromyographic characterization of myometrial contractility in pregnant rats in vivo

R. Gaspar1, R. Samavati1, K. F. Szucs1, T. Grosz2, A. Micsko3. 1University of Szeged, Pharmacodynamics and Biopharmacy H-6720. Szeged, Hungary, 2Experimetria Ltd., H-1062. Budapest, Hungary, 3MSB-MET Ltd., H-8230. Balatonfüred, Hungary

Background: Pregnant uterine contractions are led by myoelectric processes, but their physiological control is still not fully understood. In other smooth muscles, like the gastrointestinal musculature, a specialized population of interstitial cells, known as Cajal cells was discovered to be responsible for the generation of pace-making potentials. Earlier the electromyographic characterization of the gastrointestinal tract had been made and our previous results supported of these data. Recently immunohistochemically similar group of cells has been identified in the myometrium, which suggests that these Cajal-like cells may have pace-maker function in uterine smooth muscle. Aim of the study: The main aim of this study was to record and characterize the electric activity of pregnant rat myometrium in vivo. Further aims were to separate these signals from that of gastrointestinal muscles and investigate the changes in myoelectric activity of the pregnant uterus towards the end of pregnancy and by pharmacological effects. Method: Hook electrodes were placed on the surface of myometriums of 18, 20 and 22-day pregnant Sprague-Dawley rats under ketamine-xylazine-induced anaesthesia. Other hook was placed on the abdominal surface above the myometrial hook. A ground electrode was put into the tail of the animal. The electric activity was detected for 30 min periods by SPEL Advanced ISOSYS online computer system in which the software and the amplifier were designed to filter the electric signals of myocardium. The frequency of detected myometrial signals was revealed by fast Fourier transformation (FFT) and expressed as cycles per minute (CPM). The software was able to filter the wide spectra of FFT-revealed signals therefore we also filtered the CPMs characteristic for gastrointestinal tract. The intensity of the signals was evaluated by the power spectrum density (PSD). Terbutaline and sulprostone were administered intravenously via jugular vein. Results: During the experiments it was found that slow electric potentials were proper to investigate the myometrial activity. All investigated pregnancy days the characteristic CPM values of the myometria were between 15 and 25, while the PSD values have shown a continuous increase (0.017, 0.019 and 0.050 mV2) towards term. On day 22 PSD value was significantly increased (+58.6%, p<0.01) by i.v. sulprostone (10 μg/kg) treatment, while i.v. terbutaline (50 μg/kg) reduced its value (-75.9%, p<0.001). Conclusions: The electric activity of pregnant rat myometrium is well-characterized by CPM value. This CPM value is easily separable from the gastrointestinal CPM values. The PSD values express the intensity of contractions and reflect contracting and relaxing effects in the myometrum. This method allows the in vivo detection of myometrial contractility and responsiveness to pharmacological effects by non-invasive way, even in conscious animals.

This work was supported by the New Hungary Development Plan (TÁMOP-4.2.1/B-09/1/KONV-2010-0005 – Creating the Center of Excellence at the University of Szeged)