H2S concentrations in the heart after acute H2S administration: methodological and physiological considerations.

In this study, we have tried to characterize the limits of the approach typically used to determine HS concentrations in the heart based on the amount of HS evaporating from heart homogenates-spontaneously, after reaction with a strong reducing agent, or in a very acidic solution. Heart homogenates were prepared from male rats in control conditions or after HS infusion induced a transient cardiogenic shock (CS) or cardiac asystole (CA). Using a method of determination of gaseous HS with a detection limit of 0.2 nmol, we found that the process of homogenization could lead to a total disappearance of free HS unless performed in alkaline conditions. Yet, after restoration of neutral pH, free HS concentration from samples processed in alkaline and nonalkaline milieus were similar and averaged ∼0.2-0.4 nmol/g in both control and CS homogenate hearts and up to 100 nmol/g in the CA group. No additional HS was released from control, CS, or CA hearts by using the reducing agent tris(2-carboxyethyl)phosphine or a strong acidic solution (pH < 2) to "free" HS from combined pools. Of note, the reducing agent DTT produced a significant sulfide artifact and was not used. These data suggest that 1) free HS found in heart homogenates is not a reflection of HS present in a "living" heart and 2) the pool of combined sulfides, released in a strong reducing or acidic milieu, does not increase in the heart in a measurable manner even after toxic exposure to sulfide.