COMPARATIVE TOXICITY OF METHYL ISOCYANATE AND ITS HYDROLYTIC DERIVATIVES IN RATS .1. PULMONARY HISTOPATHOLOGY IN THE ACUTE-PHASE

The present study describes the acute histopathological changes induce d by methyl isocyanate (MIC) in the lungs of rats at 24 h after a sing le exposure to varied concentrations/doses of MIC by inhalation and su bcutaneous (s. c.) routes and also delineates the effects due to the h ydrolytic derivatives of MIC, viz., methylamine (MA) and N,N'-dimethyl urea (DMU). MIC, either inhaled or administered s.c., resulted in a w ide range and extent of histopathological changes in the lungs, propor tional to the exposure concentration/dose. The salient, effects of inh aled MIC are acute necrotizing bronchitis of the entire respiratory tr act accompanied by varying degrees of confluent congestion, hyperemia and interstitial and intra-alveolar edema, while MIC administered s.c. led to prominent vascular endothelial damage, congestion and severe i nterstitial pneumonitis with apparently normal bronchial epithelium; a nd intra-alveolar edema only with the high dose. The only noteworthy l esion produced by MA and DMU (to some extent) was interstitial pneumon itis, suggesting their possible involvement in the subsequent inflamma tory response of MIC. Except, for the endothelial changes, the overall spectrum of the histopathological lesions is quite comparable to thos e observed in the lungs of Bhopal victims during the acute phase.