1. INTRODUCTION
Gaseous mediators, also known as gasotransmitters, are important signalling molecules which can readily cross the cell membranes, and are endogenously produced. Signalling molecules are involved in the communication of basic cellular activities. Gasotransmitters are easily accessible to specific target molecules which larger mediators are unable to access it. CO and NO are well-known gasotransmitters. Many studies have found that H2S is a new candidate of gasotransmitter (Wang, 2002).
H2S has been shown to be involved in a variety of functions including insulin secretion, kidney function, liver function and many more (Elsey, Fowkes & Baxter, 2010). Also, they are found to have anti-oxidant and anti-inflammatory effects (Locey,
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At high concentrations, it can affect the nervous system by preventing cellular respiration, forming complex with iron in the mitochondrial cytochrome enzymes (Locey, 2005). After much research, it is now found to fit the criteria for gasotransmitters, (i) it exists as a gas, (ii) it is permeable to plasma membrane, (iii) it can be synthesised endogenously by enzymes, (iv) it has defined functions at physiological concentrations, and (v) it has specific molecular targets and its effects can be imitated with exogenous applications (Wang, 2002). There have been a lot of evidence documented regarding the therapeutic effects of H2S, mainly in cardiovascular diseases (Elsey, Fowkes & Baxter, 2010).
2.2 Therapeutic effects of H2S
H2S is reported to be a vasorelaxant of blood vessels and its effects seems to involve K+ and Ca2+ channels, though uncertain (Hart, 2011). It has also been found that H2S can produce other hypotensive effects such as regulating plasma renin levels (Lu et al., 2010) and inhibiting angiotensin converting enzyme activity in endothelial cells (Laggner et al., 2007). H2S is also involved in reducing angiotensin II production and inhibiting bradykinin degradation, thus maintaining blood pressure (Laggner et al., 2007).
H2S also plays a role in the regulation of renal function. It increases renal blood flow, glomerular filtration rate and urinary sodium and potassium secretion, hence regulating blood pressure (Hart,