This study will use nuclear imaging techniques, analysis of lung lymph, and in vivo electron dense tracers to examine trans- epithelial movement of solutes among the air, interstitial, and vascular spaces of the lungs of anesthetized sheep. The relationship between the site of solute movement through the epithelium and alveolar edema will also be studied. Our studies to date show that nuclear imaging of aerosolized 99Tc-labeled albumin clearance may be a valuable technique for detecting changes in epithelial permeability because it is non- invasive, appears to be sensitive to lung injury, and its clearance rate is unaffected by changes in lung volume. To further evaluate this technique, pulmonary and systemic lymph will be collected to monitor the appearance of the albumin in the interstitial spaces. We will compare labeled albumin to the currently popular 99Tc- DTPA (diethylenetriamine pentaacetate) for detecting physiologically relevant increases in pulmonary epithelial permeability by measuring their clearances from the lungs of sheep with lung injury induced by intravenous infusions of air or oleic acid. We will also measure the effects of increases in lymph flow and alterations in the distribution of blood flow to the tissue on the clearance of labeled albumin. To determine if the site of solute clearance is through the alveolar or extra-alveolar epithelium, colloidal gold or horseradish peroxidase will be instilled in the airspaces of anesthetized sheep that receive intravenous oleic acid and lung tissue samples will be examined under an electron microscope. Additional sheep will receive one of the tracers intravenously during the development of oleic acid-induced alveolar edema to determine if the pathways for solute clearance are the same as those through which circulating solutes enter the airways during alveolar flooding. These studies on the measurement of increased epithelial permeability and the routes of solute movement during alveolar flooding will aid in the development of improved methods for the detection, prevention and treatment of alveolar edema.