Hydrogen sulfide decreases adenosine triphosphate levels in aortic rings and leads to vasorelaxation via metabolic inhibition

Aims: Hydrogen sulfide (H2S) at low concentrations serves as a physiological endogenous vasodilator molecule, while at higher concentrations it can trigger cytotoxic effects. The aim of our study was to elucidate the potential mechanisms responsible for the effects of H2S on vascular tone. Main methods: We measured the vascular tone in vitro in precontracted rat thoracic aortic rings and we have tested the effect of different oxygen levels and a variety of inhibitors affecting known vasodilatory pathways. We have also compared the vascular effect of high concentrations of H2S to those of pharmacological inhibitors of oxidative phosphorylation. Furthermore, we measured adenosine triphosphate (ATP)-levels in the same vascular tissues. Key findings: We have found that in rat aortic rings: (I) H2S decreases ATP levels; (2) relaxations to H2S depend on the ambient oxygen concentration; (3) prostaglandins do not take part in the H2S induced relaxations; (4) the 3':5'-cyclic guanosine monophosphate (cGMP)-nitric oxide (NO) pathway does not have a role in the relaxations (5) the role of K-ATP channels is limited, while Cl-/HCO3- channels have a role in the relaxations. (6): We have observed that high concentrations of H2S relax the aortic rings in a fashion similar to sodium cyanide, and both agents reduce cellular ATP levels to a comparable degree. Significance: H2S, a new gasotransmitter of emerging importance, leads to relaxation via Cl-/HCO3- channels and metabolic inhibition and the interactions of these two factors depend on the oxygen levels of the tissue. (C) 2008 Elsevier Inc. All rights reserved.