Nongenomic action of steroids in myometrial contractility.

Steroid hormones are involved in several fundamental aspects of all living beings, with a few slight chemical differences among steroids being enough to give them the extraordinarily diverse biologic specificities that are important in animal physiology and medical therapeutics. Indeed, in the uterus, they have a remarkable action on uterine contractility with physiologic significance in the important reproductive processes of mammalian pregnancy and parturition. The regulation of progesterone on the myometrial contractile activity and related wider subjects of the endocrinology of pregnancy and parturition have been reviewed many times during the twentieth century. However, new data indicate that several progesterone metabolites and some synthetic steroids induce a progesterone-like uterine-relaxing effect. Experimental evidence from our laboratory has shown that 5-reduced progestins and androgens are more potent than progesterone itself in decreasing uterine contractility. The purpose of this review is to update current knowledge of endogenous and exogenous steroids on the phenomenon of uterine contractility, by summarizing their structural differences to induce changes on this process and discussing the possible mechanism of steroids to regulate uterine muscle activity.