H2S: an Endogenous Gas

Gases such as NO and CO play important roles both in normal physiology and in disease. In recent years, interest has been directed towards other naturally occurring gases, notably H 2 S, which is produced in body by three enzymes namely CBS (cystathionine beta synthase), CSE (cystathionine gamma lyase) and MST (3-Mercaptopyruvate sulfurtransferase), present in mitochondria and/or cytosols where main substrate is L-cysteine. Recent studies have shown that vascular tissues generate measurable amount of H2S. NO is considered as inducer for H2S. H 2 S has gained importance as a neuromodulator and a vasorelaxant factor and as the first endogenous gaseous ATP dependant K + channel opener. It potentiates LTP by enhancing NMDA induced inward current.H 2 S induces vasorelaxation, inhibits insulin secretion and also has a role in inflammation. H 2 S also appear to have a role in neuroendocrine fuction because it plays an important role in control of the hypothalamus-pitutary-adrenal axis, inhibit stimulated release of corticotropin-releasing hormone. H 2 S has been found to be decreased in patient with Alzheimer’s disease and higher concentrations are found in patients with Down’s syndrome. It has a role in development of hypertension, suggesting its role in CNS and CVS disorders. H 2 S it is well known toxic gas with the smell of rotten eggs, is now proposed as a physiologically important molecule.