[Nitric oxide--more than a vasodilator]

Endothelium-dependent vasodilation is mediated by nitric oxide (NO), which is synthesised from the amino acid arginine. The enzymes involved are present in several cell types, and NO has important regulatory functions in many of the organ systems of the body. NO seems to be of importance in the regulation of blood pressure, neuronal activity in the peripheral and central nervous systems, in ventilation perfusion-matching in the lungs, and in immune defense. Although the clinical use of nitroglycerin is more than a century old its mechanism of action, the liberation of NO, has only recently been elucidated. Endogenous nitric oxide synthesis inhibitors have been identified, and both these and NO itself are being examined in clinical trials.