Morphological and physiological study of the effect of histamine on the isolated perfused rabbit lung

Histamine causes interstitial pulmonary edema, but whether this is the result of an increased permeability of the pulmonary circulation or only of the bronchial circulation remains to be determined. In order to selectively study the effect of histamine on the pulmonary circulation, we used an isolated perfused rabbit lung preparation because in this species, the bronchial circulation is poorly developed. Edema formation was assessed by continuously monitoring the weight of the lung perfused at constant pressure. These studies were supplemented by electron microscopic observations using hemoglobin as an ultrastructural tracer for microvascular permeability. We found that histamine (8.0 microgram base/100 ml of perfusate) did not cause lung weight to increase. Ultrastructural studies showed that histamine, at this dosage, did not cause a greater leakage of hemoglobin that occurred in the control lungs. Thus, we have concluded that histamine does not increase the permeability of the pulmonary microcirculation in the isolated perfused rabbit lung.