Isoproterenol and aminophylline reduce lung capillary filtration during high permeability

Pseudomonas bacteremia in sheep causes a prolonged increase in lung vascular permeability to protein. Isoproterenol and aminophylline could effect lung fluid balance after Pseudomonas by reducing vascular pressures or by blocking release of permeability mediators. We measured vascular pressures, lung lymph flow, and lymph and plasma protein concentrations in unanesthetized sheep under baseline conditions and during steady-state increased permeability after Pseudomonas. Pseudomonas caused pulmonary vascular pressures to rise and lung lymph flow to increase fivefold, but lymph/plasma protein concentration did not change. Pulmonary vascular pressures and lung lymph flow decreased during intravenous infusion of isoproterenol and aminophylline. The decrease in lymph flow after isoproterenol and isoproterenol plus aminophylline was linearly related to the decrease in microvascular pressure (r = 0.71). Lymph/plasma total protein concentration ratios and lymph clearance of proteins with molecular radii 36--96 A remained high during isoproterenol and aminophylline. These drugs can substantially reduce transvascular filtration primarily because they reduce lung vascular pressures.