Histamine and slow reacting substance in acid-induced pneumonitis

Acid pneumonitis was produced in 18 dogs by the tracheal instillation of 3 ml/kg 0.1 N hydrochloric acid. Arterial and mixed venous oxygen tension, static compliance and pulmonary capillary wedge pressure were measured during a 2-hour observation period. Plasma histamine (measured by the enzymatic isotopic assay) increased from 1.7 +/- 0.2 ng/ml (mean +/- SE) before acid injury to 13.5 +/- 1.9 ng/ml after injury (p less than 0.05). In one group of 7 control dogs, 3 ml/kg of normal saline produced no increase in plasma histamine. Pulmonary edema secretions from acid injured animals had a histamine level of 30.3 +/- 3.8 ng/ml and slow reacting substance was detected in 7 of 11 animals. The slow reacting substance was an antihistamine-resistant, ethanol extractable substance that contracted guinea pig ileum. Lung weight-body weight ratio PaO2, and static compliance were different with acid pneumonitis compared to controls. Total protein was not different in the tracheal secretions compared to plasma. We conclude that histamine and slow reacting substance are released in this animal model of acid pneumonitis and may be important in the pathogenesis of the lung injury.