Histologic and Ultrastructural Alterations in Lungs of Rats Exposed to Sub-lethal Concentrations of Hydrogen Sulfide

Fischer-344 rats were killed 1, 18, and 42 hr after a single 4-hr exposure to an atmosphere of 0, 1 16, or 6 15 mg m-3 of hydrogen sulfide (H2S). Lungs, fixed by the intratracheal route, were examined by light and electron microscopy. Histologic changes were transient and mainly present in rats exposed to 6 15 mg m-3 H2S. Lesions included severe but transitory pulmonary edema and fibrinocellular alveolitis which was restricted to the proximal alveolar region of the lung. Electron microscopically, ciliated bronchiolar cells were the only cells that developed necrosis; they were rapidly replaced by mitosis. Alveolar endothelium had cytoplasmic blebs, but alveolar epithelium had minor changes. No mast cell degranulation was detected in lungs with edema. A 4-hr exposure to 615 mg m-3 is markedly edematogenic for the lung but only moderately cytotoxic for pulmonary cells. Hydrogen sulfide (H2S) is one of the main toxic com- pounds present in sour natural gas emissions encoun- tered in the petrochemical ind~stry.~,~ Accidental ex- posure to high concentrations of H,S-containing sour gas may be lethal for man and animal~.~,~J~ The cause of death in fatal exposure to H2S has been largely at- tributed to respiratory paralysis or a~phyxia.~ How- ever, forensic reports from humans killed in accidents involving sour gas have revealed that pulmonary ede- ma is the most notable lesion.6 Acute exposure of lab- oratory animals to H2S has corroborated these findings, suggesting that H2S-induced pulmonary edema has a threshold-type of respor~se.~,~~ Under laboratory con- ditions H,S appears to have a poor dose-effect rela- tionship in relation to edema, and once the threshold is reached, edema fluid leaks rapidly into alveolar spaces and death occurs rapidly.33 Biochemical analysis of bronchoalveolar lavage fluid collected from rats ex- posed to 560 mg m-3 H2S reveals profound alterations in vascular permeability during or immediately after a 4-hr exposure; in spite of massive pulmonary edema, the magnitude of injury to bronchoalveolar cells is only The objective of this investigation was to study histologic and ultrastructural alterations in the lungs of rats exposed to a single edematogenic concen- tration of H2S.