The effects of oxytocin on the pattern of electrical propagation in the isolated pregnant uterus of the rat

Abstract

In the isolated pregnant myometrium of the rat, the pattern of propagation was investigated by recording simultaneously from 240 different extracellular sites while the contraction of the tissue was recorded isometrically. Analysis of all recorded electrograms allowed the two-dimensional spread of activity in the myometrium to be reconstructed. From these activation maps, the conduction velocities were measured in the longitudinal, oblique and transversal directions. At low concentrations (10(-9 )and 5x10(-9) M), oxytocin significantly increased the frequency and duration of electrical bursts and the average spike intervals, without affecting the homogeneity of action potential propagation, concomitant with a significant increase in the amplitude of contractions. At high concentrations (10(-8) and 5x10(-8) M), oxytocin induced conduction blocks and the size of inexcitable areas was increased, concomitantly with an increase in muscle contractures. In contrast, the conduction velocities in the longitudinal, oblique and circular directions were not influenced by oxytocin at any concentrations.

Propagation of electrical activity in uterine muscle during pregnancy: a review

“…Being the myometrium a smooth muscle, values of propagation speed in the order of few centimetres per second could be expected (Devedeux et al 1993). While the majority of the reviewed studies, independently on the investigated species, reports figures in this range (Bozler 1938, Daniel & Renner 1960, Goto et al 1961, Wolfs & van Leeuwen 1979, Kanda & Kuriyama 1980, Wikland & Lindblom 1985, Parkington et al 1988, Miller et al 1989, Lammers et al 1999, Lammers et al 2008, de Lau et al 2013a, higher values have also been measured (Lucovnik et al 2011b). Defining a reference physiological range for the propagation speed is therefore difficult.…”

“…On isolated uterine strips of the rat, values of speed in the order of few centimetres were found in the longitudinal layers (Goto et al 1961, Kanda & Kuriyama 1980, Miller et al 1989, Lammers et al 1999. Lower figures were reported in the circumferential direction (Miller et al 1989, Lammers et al 1999 and in the transversal (Lammers et al 1999), although in the transversal segments estimation of velocity may be complicated by the complex shape and broad peaks of the spikes (Miller et al 1989).…”

“…Lower figures were reported in the circumferential direction (Miller et al 1989, Lammers et al 1999 and in the transversal (Lammers et al 1999), although in the transversal segments estimation of velocity may be complicated by the complex shape and broad peaks of the spikes (Miller et al 1989). For completeness, it may be interesting to notice that no significantly different figures were found after exposure to oxytocin (Lammers et al 1999). Still in rats, during the progress of gestation, Kanda & Kuriyama (1980) observed an increase of propagation speed; as a progressive displacement of the circumferential muscle layer from the placental region was observed, they concluded that motility of this region is mainly controlled by the longitudinal muscle layer (Kanda & Kuriyama 1980).…”

“…Recently, however, an increasing number of studies on animals and women, using high-density grids either placed directly on the uterine surface or on the abdomen, clearly show that also for the myometrium, similar to the myocardium, linear propagation of single electrical spikes occurs and that the speed of propagation can be measured (Lammers 1997, Lammers et al 1999, 1994, Rabotti & Mischi 2010, Lucovnik et al 2011b. Table 1 provides an overview of the literature reporting values of propagation speed for single electrical spikes in the uterus during pregnancy.…”

Automated Conduction Velocity Analysis in the Electrohysterogram for Prediction of Imminent Delivery: A Preliminary Study

“…While it is reasonable to hypothesize that the linearity of the propagation could be a discriminative parameter for predicting imminent delivery in itself, several aspects related to the evolution from pregnancy to labor are not yet fully understood and need further dedicated research [34]. Therefore, we excluded spikes propagating nonlinearly from the analysis as we expected those cases to be outliers, that is, to have a CV outside the physiological range reported by the previous literature [26, 35]. Only [15] reported values higher than 30 cm/s; these values cannot be considered as a physiological reference due to the specific measurement setup, which allows for information on only a projection of the CV vector [36].…”