Nitric Oxide: From the Molecule of the Year to an Important Signaling Molecule

Nitric oxide (NO) is a colorless, ubiquitous, free radical gas because of having an unpaired electron. Nitric oxide is synthesized from an amino acid called L-arginine by the action of the enzyme nitric oxide synthase (NOS) which has three important isoforms. NO has been molecule of attention because of its small size, short duration of action and variety of physiological functions. NO plays many important and critical physiological functions such as cell signaling, regulation of tone of blood vessels, neurotransmission, inflammatory processes (inhibition of leukocytic adhesion to vascular endothelium), antithrombotic effects by inhibiting platelet adhesion to vascular endothelium and the defense mechanism of the body against microorganisms. Alterations in the regulation of NO metabolism play key role in many pathological processes like development of the cancer, hypertension, obesity, atherosclerosis, preeclampsia and aging. This review will focus on its role in physiological functions in the body and alterations in some important pathological states. An insight into the functioning of this molecule will help the clinicians as well as researchers to understand the different dimensions in the pathogenesis of many diseases.