Acute toxicological studies on paraquat: pathological findings in beagle dogs following single subcutaneous injections.

Sixteen beagles were allocated into 4 groups, each group consisting of 2 males and 2 females, which were injected sc with 1,3,5 or 7 mg paraquat/kg. The beagles were observed for 2 w after the administration. At the end of the observation period all the dying and surviving dogs were studied pathologically. The LD50 was calculated as 1.8 (1.0-6.1) in males and 3.5 (2.4-10.1) mg/kg in females. Clinical laboratory tests showed increases in segmented neutrophils and monocytes, decreases in lymphocytes, slight decreases in chloride, moderate increases in BUN, GOT, GPT and phospholipids, slight increases in uric acid, total protein, creatine, total cholesterol and total bilirubin, and prolonged prothrombin times. Marked edema, congestion and hemorrhage of lungs, as well as slight congestion in various organs, were observed grossly. In histopathological examination, marked pulmonary hemorrhage and congestion, fibroblast-like cells in alveolar septa, breakdown of alveolar walls, thickening of alveolar walls and pleura, mild congestion and degeneration of the liver, and mild degeneration of renal tubules were observed. The cause of death was respiratory distress and renal failure. The surviving animals had mild atelectasis of the lungs. Electromicroscopic examination on the surviving animals revealed the appearance of spindle-shaped cells, proliferation of type II alveolar cells and fibroblasts, mitosis of fibroblasts, and abundant collagen fiber in the lung, calcium deposition, stratification and thickening of basement membranes, and localized necrotic epithelial cells in the proximal tubules of kidneys, and stratification of intramitochondrial cristae of the liver. Pulmonary fibrosis in the switchover stage was present with participation from type II alveolar cells, fibroblasts and myofibroblasts.