Nitric Oxide: No Laughing Matter

Abstract

Nitric oxide (NO), long known as an environmental pollutant in cigarette smoke and smog, recently was found to have a wide variety of biological and physiological functions. NO is a simple molecule that exists as a colorless, lipophilic gas and is rapidly inactivated to nitrate and nitrite through oxidation. Produced endogenously, NO has been identified in many cell types including endothelial cells, vascular smooth muscle, cerebral astroglia, microglia, and macrophages. Now recognized as a major endogenous mediator of multiple physiologic processes (including the regulation of vascular tone), it has been named endothelium-derived relaxation factor. Other actions include effects on platelet aggregation, neurotransmission and neuromodulation, intracellular and intercellular signalling capabilities, and cytotoxic and cytostatic actions. NO secreted by macrophages and neutrophils is an important cytotoxic effector molecule in the defense against tumor cells, parasites, bacteria, and fungi.