Nitric Oxide (NO) is produced in the body by a group of enzymes called NO synthases (Nos). These enzymes generate NO by converting the substrate, the semi essential amino acid, arginine, to citrulline and NO. Nos exist as a normal constituent of cells (constituent or cNos) or could also be generated de novo in response to various stimuli (inducible or iNos). NO is essential to normal mammalian physiology. As the endothelium derived relaxing factor, it regulates the vascular tone to maintain the normal systemis, pulmonary and regional hemodynamics. It influences platelet function and is an important constituent of antimicrobial defense and serves as the neurotransmitter of the non-adrenergic non-cholinergic nerves.NO administered by inhalation as a pulmonary vasodilator has advantages over other vasodilators in that it preserves the ventilation-perfusion matching in the lung and thus supports the normal oxygenation of the venous blood. Inhaled NO is now used to treat pulmonary hypertension and right sided heart failure. It is also used as a diagnostic test for persistent asthma and as a test for the reversibility of pulmonary hypertension. Other related compounds such as nitrate vasodilators and phosphodiesterase 4 inhibitors act by releasing NO. Arginine might increase production of endogenous NO and could be used therapeutically. As NO is also a diatomic free radical and a potent inflammatory agent, inhibitors of NO may have a role in the therapy of selected inflammatory conditions. The present article provides is a brief review of the pharmacology and therapeutic uses of NO and related drugs.
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