Nitric oxide

Nitric oxide, known chemically as NO, is an air pollutant caused by the use of fossil fuels, but in the 1980s NO was also discovered to be a free radical with many vital roles in the human body, including acting as s unique kind of transmitter for the nervous system. The process of NO synthases synthesizes NO from the amino acid L-arginine.

NO has a number of roles in the respiratory system, including promoting vascular and bronchial dilation, and mucus secretion, and it is an important neurotransmitter for nonadrenergic, noncholinergic neurons in the bronchial wall. NO can also influence inflmmatory cells, and is a mediator of inflammatory phenomena within lungs cells.

Learn more
Nitric oxide - Encyclopedia of Neuroscience

Nitric oxide and it's possible role in ME/CFS - Andrew Gladman