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5 out of 10

Regarding nitric oxide, false is: (AIIMS NOV 2007)

A Seen in the lung of smokers

B Increases cAMP levels

C Used to treat hypertension

D All are true

Ans. B Increases cAMP levels

I. Many different stimuli act on the endothelial cells to produce endothelium-derived relaxing factor (EDRF), a substance that is now known to be nitric oxide (NO).

II. NO is synthesized from arginine in a reaction catalyzed by nitric oxide synthase (NO synthase, NOS). three isoforms of NOS have been identified: NOS 1, found in the nervous system; NOS 2, found in macrophages and other immune cells; and NOS 3, found in endothelial cells. NOS 1 and NOS 3 are activated by agents that increase intracellular Ca2+ concentration, including the vasodilators acetylcholine and bradykinin.

III. The NOS in immune cells is not induced by Ca2+ but is activated by cytokines.

IV. The NO that is formed in the endothelium diffuses to smooth muscle cells, where it activated soluble guanylyl cyclase, producing cGMP, which in turn mediated the relaxation of vascular smooth muscle. NO is inactivated by hemoglobin.