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

In the isolated pregnant myometrium of the rat, the pattern of propagation was investigated by recording simultaneously from 240 different extracellul ar sites while the contraction of the tissue was recorded isometrically. An alysis of all recorded electrograms allowed the two-dimensional spread of a ctivity in the myometrium to be reconstructed. From these activation maps, the conduction velocities were measured in the longitudinal, oblique and tr ansversal directions. At low concentrations (10(-9) and 5x10(-9) M), oxytoc in significantly increased the frequency and duration of electrical bursts and the average spike intervals, without affecting the homogeneity of actio n potential propagation, concomitant with a significant increase in the amp litude of contractions. At high concentrations (10(-8) and 5x10(-8) M), oxy tocin induced conduction blocks and the size of inexcitable areas was incre ased, concomitantly with an increase in muscle contractures. In contrast, t he conduction velocities in the longitudinal, oblique and circular directio ns were not influenced by oxytocin at any concentrations.