The effect of oxytocin on uterine contractility and electromyographic activity recorded from the rat abdominal

OBJECTIVES: To determine if the electromyographic (EMG) recording of uterine activity obtained from the abdominal surface can be used as a non-invasive measure of uterine contractility and if the electrical power density spectrum (PDS) correlates with the efficiency of oxytocin stimulation in the rat. STUDY DESIGN: EMG activity was acquired by use of unipolar electrodes attached simultaneously to the uterine wall (UT) and abdominal surface (AS). EMG activity was recorded in the 0.3 - 50 Hz range and digitized at 200 samples/s. Intrauterine pressure (IUP) was measured continuously using a catheter implanted in the uterus. The effect of additive doses of oxytocin on PDS and integrated IUP was recorded in the anesthetized rats at term. RESULTS: Bursts of EMG activity recorded from AS mirrored those from the UT, albeit at a lower amplitude. At lower oxytocin concentrations, PDS energy and IUP increased and contractions were phasic with return to the baseline in between. As oxytocin concentration increased, the energy declined while the IUP continued to rise (figure). This increase was due to the onset of tetanic contractions and a progressive increase in the baseline tone. CONCLUSIONS: Uterine electrical activity can be reliably recorded from the abdominal surface and may be a useful, non-invasive, method to study myometrial function and pharmacology in-vivo. Analysis of the uterine electrical energy may be a better indicator of the efficiency of myometrial contraction than pressure or traditional tocodynamometry alone. Additional studies to evaluate this technology in humans are warranted.