Hydrogen sulfide: third gaseous transmitter, but with great pharmacological potential

Hydrogen sulfide (H₂S), which is well known traditionally as a toxic gas, has been proven to be produced endogenously by 3 enzymes in mammalian tissues and plays important roles in physiological and pathophysiological conditions. In the central nervous system, H₂S functions as not only a neuromodulator, but also a neuroprotectant against oxidative stress. In the cardiovascular system, H₂S relaxes vascular smooth muscles by the activation of K_ATP channels and inhibits smooth muscle cell proliferation via the mitogen-activated protein kinase signaling pathway. These effects are important for maintaining blood pressure and preventing vessel structural remodeling, and identifies H₂S as an important factor in the development of some vascular diseases, such as hypertension. H₂S also shows cardioprotective effects in ischemic myocardium and septic and endotoxin shock. Recent studies have demonstrated a new mechanism to explain the motor effect of H₂S on the rat detrusor muscle, which is through the activation of the capsaicin-sensitive primary neuron. This review focuses on the recent research achievements on H₂S and discloses the great potential of H₂S as the third gaseous transmitter in cardiac protection.