The Vital Role of Nitric Oxide

Nitric oxide (NO) was among the first gases to be discovered. It was discovered by Joseph Priestley in 1772—two years after his discovery of oxygen (O2). For more than two centuries this colorless and odorless gas was considered highly toxic. Several chemists have died of what we now call toxic-shock syndrome, after purposely or accidentally inhaling large amounts of it. No one anticipated that small quantities of this lethal agent would have a crucial function in humans and probably all other animals. During the last ten years, this belief was dramatically changed when several discoveries were made, revealing a significant biological role for NO. First, in 1980, Furchgott & Zawadzki reported that endothelial cells release a substance which is responsible for the relaxation of vascular smooth muscle (they called this substance endothelium-derived relaxing factor-EDRF). Then in 1987 Palmer, Ferrige & Moncada suggested that EDRF is NO which is produced by the oxidation of L-arginine. In 1992 Malinski finally proved this suggestion by direct in situ measurement of NO in a single endothelial cell. Since then about 27,000 scientific papers have been published dealing with different aspects of NO in biological systems. NO in aqueous systems is moderately reactive; it reacts with oxygen to produce nitrite and subsequently nitrate. The average half-life of NO in tissue is about 3–6 seconds and in