Oxygen deficit and H2S in hemorrhagic shock in rats

INTRODUCTION Hemorrhagic shock induced O2 deficit triggers inflammation and multiple organ failure (MOF). Endogenous H2S has been proposed to be involved in MOF since plasma H2S concentration appears to increase in various types of shocks and to predict mortality. We tested the hypothesis that H2S increases during hemorrhagic shock associated with O2 deficit, and that enhancing H2S oxidation by hydroxocobalamin could reduce inflammation, O2 deficit or mortality. METHODS We used a urethane anesthetized rat model, where 25 ml/kg of blood was withdrawn over 30 minutes. O2 deficit, lactic acid, tumor necrosis factor (TNF)-alpha and H2S plasma concentrations (Siegel method) were measured before and after the bleeding protocol in control animals and animals that received 140 mg/kg of hydroxocobalamin. The ability to oxidize exogenous H2S of the plasma and supernatants of the kidney and heart homogenates was determined in vitro. RESULTS We found that withdrawing 25 ml/kg of blood led to an average oxygen deficit of 122 ± 23 ml/kg. This O2 deficit was correlated with an increase in the blood lactic acid concentration and mortality. However, the low level of absorbance of the plasma at 670 nm (A670), after adding N, N-Dimethyl-p-phenylenediamine, that is, the method used for H2S determination in previous studies, did not reflect the presence of H2S, but was a marker of plasma turbidity. There was no difference in plasmatic A670 before and after the bleeding protocol, despite the large oxygen deficit. The plasma sampled at the end of bleeding maintained a very large ability to oxidize exogenous H2S (high μM), as did the homogenates of hearts and kidneys harvested just after death. Hydroxocobalamin concentrations increased in the blood in the μM range in the vitamin B12 group, and enhanced the ability of plasma and kidneys to oxidize H2S. Yet, the survival rate, O2 deficit, H2S plasma concentration, blood lactic acid and TNF-alpha levels were not different from the control group. CONCLUSIONS In the presence of a large O2 deficit, H2S did not increase in the blood in a rat model of untreated hemorrhagic shock. Hydroxocobalamin, while effective against H2S in vitro, did not affect the hemodynamic profile or outcome in our model.