EFFECTS OF HISTAMINE AND ACETYLCHOLINE ON THE ISOLATED PERFUSED LUNG LOBE

¹ Department of Cardiology, Division of Medicine City of Hope Medical Center, Duarte, California 91010 and the Department of Medicine, University of Southern California School of Medicine, Los Angeles, California

Osmotic, surfactive, and hydrostatic forces were controlled in the Ringer-Locke perfused, isolated lung lobe of the dog. Changes in the volumes of the airway space and of the total lobe, and in the rate of flow through the vascular bed were recorded. Each injection of acetylcholine (5·6 to 176 ng per gram of lung lobe) or histamine (42 to 139 ng per gram of lung lobe) was followed by an immediate shrinkage of the lobe and by a slightly delayed extrusion of fluid from the airway. The fall in pulmonary vascular conductance (flow rate/arteriovenous perfusion pressure) varied with the instantaneous difference in the changes of the total lung volume and of the airway volume. It appears that as acetylcholine or histamine causes contraction of the smooth muscle of the airways, the lung shrinks and the airway pressure rises. The lowered alveolar capillary transmural (vascular minus airway) pressure collapses the capillaries and reduces pulmonary vascular conductance. The effects on vascular conductance are due to the altered airway resistance rather than to direct effects on the blood vessels.

Note:

This investigation was aided by Grant HE 08721 from the National Heart Institute of the United States Public Health Service.