The blood/air barrier as defined by horseradish peroxidase in the normal guinea pig lung

Abstract

The blood/air barrier is established by the combined influences of the capillary endothelial cells, the interstitial space and the alveolar epithelial cells. The present study examined the morphological basis of the blood/air barrier as defined by a tracer model. This barrier is altered in many pathological states as reflected by the presence of exudate and/or increased cellularity in the alveoli. This investigation provides comparative data which can be used to assess early changes and potential recovery of barrier integrity whether response is caused by internal physiological alterations or external toxic stimuli.A small molecular weight protein, horseradish peroxidase (HRP), was used in the guinea pig model to ultrastructurally show the existence of a barrier at the level of the alveolar epithelium. Adult animals were injected intravenously with 300 mg/kg of the tracer in a small volume of saline (4% of total blood volume) and sacrificed at varying intervals by either intratracheal filling or right-ventricular perfusion with a fixative consisting of 3% glutaraldehyde buffered with 0.1M phosphate.