Nitric oxide in the human uterus

Nitric oxide (NO) plays a crucial role in many biological systems. Recent evidence indicates that NO is found in the human uterus. During pregnancy, it is produced in the placenta, the decidua and the myometrium. In the nonpregnant state, nitric oxide synthase, the enzyme that catalyses the production of NO, has been identified in both the myometrium and the endometrium. Potential roles for NO in the human uterus are speculative, but include vasodilatation (both before implantation, and in the uteroplacental and systemic circulation during pregnancy), inhibition of platelet activation during menstruation, and suppression of myometrial contractility during pregnancy. Nitric oxide may also be involved in uterine pathology. Excessive NO production by the uterus during menstruation could lead to menorrhagia. During pregnancy, a change in NO production may be implicated in pre-eclampsia, and animal studies have shown that inhibition of NO production leads to intrauterine growth retardation. If a role for NO is confirmed in these various uterine conditions, pharmacological modification of NO activity may lead to novel therapeutic applications. However, these notions are still conjectural, and extensive work is required before such treatments can be introduced into clinical practice.