Hormonal Effects on Human Myometrial Activity

Abstract

Literature on the effects of hormones on human myometrial activity is reviewed. The effects of estrogens, gestagens, and prostaglandins on myometrial activity in pregnant and nonpregnant women, and those of maternal and fetal corticosteroids, biogenic amines, and oxytocin and vasopressin are discussed. Estrogens produce small, frequent, local, and nonpropagated contractions of the myometrium, while gestagens produce contractions of higher amplitude, longer duration, and lower frequency. Maternal and fetal corticosteroids have some importance for myometrial activity of pregnancy in some animals, but their role in humans remains obscure. Epinephrine and norepinephrine stimulate myometrial activity in humans, though their physiologic and therapeutic importance is doubtful. The same holds for serotonin. Oxytocin in large doses stimulates myometrial activity during the proliferative stage of the cycle, but is without effect in smaller doses. During pregnancy, oxytocin progressively stimulates myometrial activity, particularly toward the end of pregnancy. Oxytocin is often used to initiate and stimulate labor. Vasopressin, on the other hand, stimulates myometrial activity during the secretory phase of the cycle, especially around the onset of menstruation. Vasopressin has a less marked effect during pregnancy than oxytocin, and its effects are not enhanced as pregnancy comes to term. The fetus is known to produce considerable amounts of oxytocin and vasopressin during labor, though the significance of this contribution remains to be elucidated. Prostaglandins have a potent stimulatory effect on myometrial activity in both pregnant and nonpregnant women. The possibility that prostaglandins play a physiologic role in the onset of myometrial activity remains to be determined.