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Medical Term:

nitric oxide

Pronunciation: ni'trik oks'id

Definition: A colorless free-radical gas that reacts rapidly with O2 to form other nitrogen oxides (e.g., NO2, N2O3, N2O4) and ultimately is converted to nitrite (NO2-) and nitrate (NO3-); a gaseous mediator of cell-to-cell communication and potent vasodilator, formed from l-arginine in bone, brain, endothelium, granulocytes, pancreatic beta cells, and peripheral nerves by a constitutive nitric oxide synthase, and in hepatocytes, Kupffer cells, macrophages, and smooth muscle by an inducible nitric oxide synthase (e.g., induced by endotoxin). NO· activates soluble guanylate cyclase, mediates penile erection, and may be the first known retrograde neurotransmitter.

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