A comparative study of the pulmonary effects of NO2 in the rat and hamster.

A study of the response of rat and hamster to nitrogen dioxide (NO2) under identical conditions has been undertaken. Exposure to 20 parts/IO6 NO2 for 24 h produced a mild cytotoxic effect on the terminal bronchiole and proximal alveoli in the rat, whereas the hamster developed a moderate to severe bronchiolitis and alveolitis. Electron microscopic examination of tissue sections showed accumulation of surfactant in lamellar bodies of the alveolar type II cell in the rat but not in the hamster, whereas in the hamster Clara cells were observed in mitosis. Increased levels of surfactant isolated from whole lung homogenates by sucrose gradient centrifugation were found in both rat and hamster. In contrast surfactant isolated from bronchiolo-alveolar lavage was increased only in the hamster. The results suggest that caution must be exercised in the choice of animal model in investigations aimed at the understanding of the toxicological effects of nitrogen dioxide in man.