The primary action of Nitric oxide (NO) in the gastrointestinal tract is -

Ans. is 'c' i.e., Gastrointestinal smooth muscle relaxation "Nitric oxide (NO) seems to be involved as neurotransmitter in nonadrenergic noncholinergic (NANC) smooth muscle relaxation thoughout the gastrointestinal tract". --Interneto This question is a direct repeat from All-India 2010.Actions of NOo NO has following actions : -i) 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 endothelialcells 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,ii) NO acts as short lived biological messenger by stimulating a guanyl cyclase that produce cGMP and cGMP activates protein kinase Giii) NO inhibits platelets adhesion, activation and aggregation.iv) NO acts as gaseous neurotransmitter in brain and peripheral autonomic system. NO acts as a mediator of long term potentiation, cytotoxicity resulting from NMDA and nonadrenergic noncholinergic neurotransmission.v) In the immune system, NO serves as an effector of macrophage induced cytotoxicity, and overproduction of NO is a mediator of inflammation - Inhibitors of iNOS have a protective effect on arthritis, psoriasis & IBD.vi) NO decreases LDL oxidation and inhibits superoxide anion (O-2) production by inhibiting NADPH reductase activity. These actions result in a strong antiatherosclerotic effect.vii) Recent studies have provided important information on the use of inhaled nitric oxide for the management of several diseases characterized by the presence of abnormal pulmonary' vascular tone, such as persistent pulmonary hypertension of the newborn.