Inhaled hydrogen sufide - A rapidly reversible inhibitor of cardiac and metabolic function in the mouse

Background: Breathing hydrogen sulfide (H2S) has been reported to induce a suspended animation-like state with hypothermia and a concomitant metabolic reduction in rodents. However, the impact of H,S breathing on cardiovascular function remains incompletely understood. In this study, the authors investigated the cardiovascular and metabolic effects of inhaled H2S in a murine model. Methods: The impact of breathing H2S on cardiovascular function was examined using telemetry and echocardiography in awake mice. The effects of breathing H2S on carbon dioxide production and oxygen consumption were measured at room temperature and in a warmed environment. Results: Breathing H2S at 80 parts per million by volume at 27 degrees C ambient temperature for 6 h markedly reduced heart rate, core body temperature, respiratory rate, and physical activity, whereas blood pressure remained unchanged. Echocardiography demonstrated that H2S exposure decreased both heart rate and cardiac output but preserved stroke volume. Breathing H2S for 6 h at 35 degrees C ambient temperature (to prevent hypothermia) decreased heart rate, physical activity, respiratory rate, and cardiac output without altering stroke volume or body temperature. H2S breathing seems to induce bradycardia by depressing sinus node activity. Breathing H2S for 30 min decreased whole body oxygen consumption and carbon dioxide production at either 27 degrees or 35 degrees C ambient temperature. Both parameters returned to baseline levels within 10 min after the cessation of H2S breathing. Conclusions: Inhalation of H2S at either 27 degrees or 35 degrees C reversibly depresses cardiovascular function without changing blood pressure in mice. Breathing H2S also induces a rapidly reversible reduction of metabolic rate at either body temperature.