Evaluation of the functional integrity of endothelium in perfused lungs

Prostacyclin (PGI2) formation and the saturable uptake of 5-hydroxytryptamine (5HT) were studied as indices of endothelial integrity in isolated lungs. 5HT uptake was characterized by its kinetic parameters Km and Vmax. These were calculated from multiple indicator dilution data on the basis of an organ model of 5HT uptake. Perfused dog lung lobes were exposed to plasma activated with yeast (YAP) or zymosan (ZAP). YAP induced a transient elevation of Km. This increase probably reflects endothelial injury. Vmax remained unchanged, suggesting that the perfused endothelial surface remained stable. PGI2 biosynthesis was negligible in the control period, but started immediately after exposure to ZAP or YAP. It was proportional to the transient elevation of Km and to the pulmonary oedema. The data suggest that PGI2 might be a marker of severe endothelial distress.