Placenta and myometrial block

The fluorescent dye method of Mashima and Csapo was employed in a study of the propagated activity of the pregnant rabbit uterus.Mechanical activity induced by stimulating one end of an 8 cm. long uterine strip was well conducted along the entire length of the postpartum uterine strip. This is evidence of propagation. The extent of activity was dependent on the strength and duration of electrical stimulation, as characteristic of excitable tissues.The uterus in early pregnancy (before implantation) showed activity strictly restricted to the stimulated portion, due to a uniform block exerted on the entire length of the uterine horn. In the late pregnant uterus the block was no longer uniform but it was restricted to the placental portion of the uterine wall. The interplacental regions and the nonpregnant horn of the pregnant uterus did propagate the wave of activity to some extent. This segmental distribution of propagating and nonpropagating regions, in the pregnant uterus, results in functional inhomogeneity.Functional inhomogeneity is characteristic of the rabbit uterus in late pregnancy; the pregnant horn becomes fully propagating and of uniform activity after the placenta is born, or if placental function is suspended before term.