Nitric oxide and the myometrium.

Nitric oxide (NO) is a potent smooth muscle relaxant in blood vessels, the gastrointestinal tract and the respiratory system. Recent evidence has shown that NO has a relaxant (tocolytic) effect on myometrium. NO is produced within the female genital tract during pregnancy, and a reduction in NO synthesis may be involved in the initiation of parturition. Furthermore, the administration of NO donors may be useful in inhibiting uterine contractions in situations where such activity is unwanted, e.g., in preterm labour. NO is also produced in the myometrium in the nonpregnant state, and has potential roles in the facilitation of implantation and the prevention of dysmenorrhoea. This article aims to examine the evidence suggesting that NO has a physiological role in the maintenance of pregnancy and potential pharmacological use in the treatment of preterm labour.