H. Pearson

Pathology of acute respiratory distress in the dog associated with paraquat poisoning

Abstract The morbid anatomical, histological and ultrastructural changes in the lungs of 10 dogs with acute respiratory distress are described. The duration of signs varied from 12 h to 7 days. The early phase of respiratory distress was associated with pulmonary haemorrhage and oedema, focal necrosis of bronchiolar epithelium, alveolar collapse and loss of both type I and type II pneumonocytes. In the later stages there was intra-alveolar fibrosis, bronchiolar epithelial regeneration and alveolar epithelialization by immature type II pneumonocytes. Paraquat was recovered from 4 of the dogs and the similarity between the clinical and pathological features within the group, and to paraquat poisoning in other species, suggested that this compound was probably responsible for the lesions in all 10 dogs. Histological changes also included necrosis of the adrenal zona glomerulosa, renal tubular necrosis, focal myocardial necrosis and medial fibrinoid necrosis of coronary arteries, a change not hitherto described in association with paraquat poisoning. The lesions are discussed in relation to their possible functional role in the development of clinical signs, and are compared with the lesions of paraquat poisoning which have been described in man and laboratory animals.