<prompt> Mechanism of action of nitric oxide isIncrease cAMPIncrease cGMPIncrease PGE2Increase PGD4  <response>: Refer kDT 7e 568 Nitric oxide nitrogen oxide or nitrogen monoxide is a colorless gas with the formula NO. It is one of the principal oxides of nitrogen. Nitric oxide is a free radical, i.e., it has an unpaired electron, which is sometimes denoted by a dot in its chemical formula, i.e., NO. Nitric oxide is also a heteronuclear diatomic molecule, a historic class that drew researches which spawned early modern theories of chemical bonding. 