In vitro motility of non-pregnant rat uterine horns

The in vitro spontaneous mechanical and electrical activity of the non-pregnant rat uterine horn was investigated. An isometric isovolumic preparation was used to obtain records of intraluminal pressure, axial force, extracellular electrical activity and horn morphology. Mean intraluminal pressure was 28.6 cmH2O and mean force 2.5 g. Burst electrical activity was initiated at the ovarian end in 70% of the cases. Detailed analysis of electrical and mechanical events during a single contraction showed a preparatory phase involving the longitudinal muscle layer, followed by a stronger contractile event involving both longitudinal and circular layers. Moreover, the mechanical activity was modulated at the frequency of a component (0.16-0.20 Hz) of the slow electrical activity of the horn. Burst electrical activity appeared at five equidistant electrodes along the horn with variable delays: the highest delays (mean values 7.4 s for burst activity initiated at the ovarian end and 6.5 s at the vaginal end) were observed in the middle part of the horn. The spontaneous contraction of the segment appeared to be due to the activation of separate regions of the horn (i.e. an ovarian and a cervical region), more than to a propagated excitatory action.