Nitric oxide in the human uterus

In 1987, the gas nitric oxide (NO) was shown to possess the physical and pharmacological properties of Furchgott’s endothelium-derived relaxing factor (EDRF). It is now recognized that this ubiquitous molecule plays a crucial role in a host of biological systems (Furchgott and Zawadzki, 1980; Palmer et al., 1987; Moncada and Higgs, 1993; Anggard, 1994). Nitric oxide is a smooth muscle relaxant in the vascular system, lungs and the gastrointestinal tract. It is a neurotransmitter in the brain and peripheral nervous system, and is involved in activities as diverse as memory and insulin release from islet cells. Furthermore, NO is produced by macrophages and other cells of the immune system in large quantities as part of the defence mechanism against foreign organisms and malignant cells. Given the pervasive nature of NO, it is not surprising that it is produced by and intimately involved in the functions of the female reproductive tract. For example, it may play a role in regulating blood loss during, and preventing the development of intrauterine adhesions following, menstruation. In pregnancy, NO may be involved in the regulation of blood flow through the fetoplacental circulation and it may be pivotal for the maintenance of myometrial quiescence. This review aims to examine the sites of production and the function of NO in the human uterus. In each situation in which a role for NO has been proposed in women, results will be supported by studies using animal models.