Ultrastructural changes in rat lung arterioles in conditions of altered permeability

By means of the colloidal carbon technique and injection of a barium-gelatin mixture into the pulmonary artery, the ultrastructure of lung arterioles in a state of increased permeability has been studied. In certain conditions pulmonary arteriolar permeability changes are frequent and the carbon particles adhere to the endothelium. Leakage of carbon into the interstitial space is observed only rarely. It is concluded that the pulmonary and systemic vessels have different patterns of response to altered permeability.