DESPITE extensive research in muscle and reproductive physiology, the factors controlling the onset of labor are still far from clear. Experimental work in animals1-3 has suggested that during pregnancy the myometrium overlying the placenta is inhibited and less excitable than interplacental myometrium, probably due to the local effect of placental progesterone. This difference, however, disappears at or near term allowing the uterus to contract in synchrony. Since the data obtained from animals may not necessarily be applicable to the human pregnant uterus, we have studied the comparative profiles in myometrium overlying the placental and antiplacental sites for ions, resting membrane potential, actomyosin-like protein, and the high-energy phosphates, adenosine-triphosphate (ATP) and phosphocreatine (PC), in human pregnancy for the first time.
Biopsy specimens from women at various stages of pregnancy were obtained from the myometrium overlying the placental and antiplacental sites during elective cesarean section, cesarean hysterectomy and therapeutic abortion. Ionic