Pulmonary Endothelial Angiotensin Converting Enzyme Activity in Lung Injury

Abstract

The intimai lining of all blood vessels is composed of a single continuous layer of simple squamous epithelial cells of mesenchymal origin, which are called endothelial cells. In the past, vascular endothelium was mainly credited for being part of the semi-permeable barrier that separates blood from the surrounding tissues and, in the lungs, blood from air. However, extensive research performed during the last twenty-five years proved that the aforementioned ‘static’ endothelial feature was false, and that vascular endothelium is instead a ‘dynamic’ organ possessing numerous physiologic, immunologic, and metabolic functions. In the human lung, endothelial cells occupy an area with a surface of approximately 130 m² [1]. The strategic location of the lungs, and the tremendous surface area of the pulmonary capillary endothelium allows the latter to filter the entire circulating blood volume before it enters the systemic circulation. Thus, pulmonary endothelial functional and structural integrity are essential for adequate pulmonary and systemic cardiovascular homeostasis.