Patterns of uterine myoelectrical activity in reproductively normal mares in late gestation and in mares with experimentally induced ascending placentitis

摘要

Mares that develop ascending placentitis in late gestation are frequently treated empirically with progestins because it is theorized that placentitis induces uterine contractions and progestins promote uterine quiescence. However, data on the pattern of myometrial activity in the late gestational mare are limited [1] and there are no data on mares with placentitis. Two patterns of myoelectrical activity, the primate and ruminant, have been described in late pregnancy. In the primate, the uterus begins to contract in the evening 10-14 days before parturition. The lengths of time the uterus contracts increases progressively each evening until labor commences [2]. In the ruminant, the uterus starts to contract about 24 h before parturition and continues until the neonate is delivered [3]. We hypothesized that the pattern of uterine myometrial electrical activity in the late gestational mare is similar to that of the primate and that ascending placentitis disrupts this pattern resulting in premature labor.