Acute hydrogen sulfide poisoning. Demonstration of selective uptake of sulfide by the brainstem by measurement of brain sulfide levels.

The possibility of measuring sulfide levels in the central nervous system (CNS) opens up many avenues for exploration. In acute hydrogen sulfide (H2S) poisoning, death results from loss of central respiratory drive. To date, however, measurement of brain sulfide has not been possible. By employing gas dialysis and ion chromatography coupled to electrochemical detection, rat brain sulfide levels could be measured either following inhalation of H2S or after injection of sodium hydrosulfide (median lethal dose, [LD50] = 14.6 +/- 1.00 mg/kg). Accumulation of brain sulfide was linearly proportional to the dose over the range 0.50 LD50 to 3.33 LD50 units, and was strongly correlated with mortality data (R = 0.947). Furthermore, analysis of untreated (control) brain showed an endogenous sulfide level of 1.57 +/- 0.04 micrograms/g (mean +/- SE; N = 16). Studies on various rat brain regions (brainstem, cerebellum, hippocampus, striatum and cortex) showed that the endogenous sulfide level of brainstem, 1.23 +/- 0.06 micrograms/g, was significantly lower than that of the other brain regions. Net uptake of sulfide was greatest in the brainstem (3.02 micrograms/g) compared to the other regions as was the selective accumulation of sulfide as calculated from normalized blood flow rates. The results of subcellular fractionation demonstrated that sulfide was detectable in fractions enriched in myelin, synaptosomes and mitochondria. Approximately one-quarter of the endogenous sulfide content of whole rat brain was found in the mitochondrial fraction. The sulfide content of these fractions increased 2- to 3-fold after 50 mg/kg NaHS, the greatest increases occurring in myelin- and mitochondrial-enriched fractions.