NO is released by -

Ans. is 'c' i.e., Endothelial cells o The most important physiological source of NO is endothelial cells.o Nitric oxide, also called endothelium-derived-relaxing factor (EDRF), is formed from amino acid arginine, by the action of the enzyme NO synthase, which is cytosolic.o NO acts as short lived biological messenger by stimulating a guanyl cyclase that produce cGMP and cGMP activates protein kinase G.o The most important actions is the relaxation of smooth muscles. The constant release of NO from endothelial cells produces vasodilatation, and basal release of NO produced by endothelial cells is a primary determinant of resting vascular tone. In GIT, NO produces relaxation of GI smooth muscles. Vasodilatation in corpora covernosa helps in penile erection.o NO inhibits platelets adhesion, activation and aggregationo Cigarette smoking decreases endogenous NO formation