The effects of endogenous and exogenous histamine on pulmonary alveolar membrane permeability.

The effects of exogenously administered histamine phosphate (0.1 microgram per kg of body weight per min, or 90 microgram per hour) and endogenous histamine released by intravenous injection of 0.5 mg of Compound 48/80 on alveolar membrane permeability to substances of differing molecular weight (60 to 20,000 daltons) were studied using the in vivo saline-filled dog lung model. The half-time, i.e., the time required for 50 per cent equilibration between tracer substances in the blood compared to the saline-filled lung, was measured at baseline for urea, sucrose, and dextrans of varying molecular weight. The half-time decreased significantly for substances as large as 10,000 daltons after histamine infusion, and 20,000 daltons after injection of Compound 48/80. We conclude that histamine can increase alveolar epithelial permeability for substances of low molecular weight.