Pathogenesis of paraquat-induced pulmonary hemorrhage in hamsters with special reference to arterial constriction.

Three dimensional reconstructions of pulmonary arteries and the bronchial tree were made to evaluate the cause of hemorrhage in the lungs of hamsters treated with a single intraperitoneal injection of paraquat at a dose of 15 mg/kg b.w. The hemorrhage corresponding to the respiratory bronchiolar segment formed the minimum hemorrhagic unit; larger hemorrhages were composed of conglomerations of such units. The respiratory bronchiolar segment was fed by a single respiratory bronchiolar arteriole which had a distinct muscular medial coat. No evidence of breakage of the arterial wall passing through the hemorrhagic lesion could be detected even by careful observation with serial histological sections. Accordingly, the cause of the lung hemorrhage was sought in the combined effects of paraquat toxicity to the capillary endothelium and vasoconstriction of the respiratory bronchiolar arterioles.