Myometrial maturation and labour

Abstract

The increased expression of contraction-associated proteins, including oxytocin receptors, connexin-43, and prostaglandin F2alpha receptors, in term pregnant myometrium is classically considered to be the concrete expression of myometrial activation. However, the decrease in prostaglandin E2 receptor subtype EP2 on one hand and the down-regulation of the nitric oxide (NO) pathway and various vasorelaxing peptides on the other hand probably also play a key role in the loss of quiescence, and, with the above-mentioned activation, in the maturation of the myometrium. Decidual activation and production of interleukin-1, tumour necrosis factor-alpha and epidermal growth factor enhance prostaglandin production in both the amnion and chorion, and also in the myometrium. A substantial increase of eicosanoids concentration in myometrial tissue is probably an important condition for the success of the ultimate step of myometrial stimulation and the onset of labour. During labour, prostaglandins and oxytocin seem to act in synergy, perhaps along with endothelin-1, to trigger contractility through an increase in intracellular Ca2+ concentration. An overall view of these phenomena in which myometrial cells are the common targets of uterorelaxant and uterotonic agents appears essential for a rational use of tocolytic therapies and labour inductors.