Isoproterenol attenuates high vascular pressure-induced permeability increases in isolated rat lungs

To separate the contributions of cellular and basement membrane components of the alveolar capillary barrier to the increased microvascular permeability induced by high pulmonary venous pressures (Ppv), we subjected isolated rat lungs to increases in Ppv, which increased capillary filtration coefficient (Kfc) without significant hemorrhage (31 cmH2O) and with obvious extravasation of red blood cells (43 cmH2O). Isoproterenol (20 microM) was infused in one group (Iso) to identify a reversible cellular component of injury, and residual blood volumes were measured to assess extravasation of red blood cells through ruptured basement membranes. In untreated lungs (High Ppv group), Kfc increased 6.2 +/- 1.3 and 38.3 +/- 15.2 times baseline during the 31 and 43 cmH2O Ppv states. In Iso lungs, Kfc was 36.2% (P < 0.05) and 64.3% of that in the High Ppv group at these Ppv states. Residual blood volumes calculated from tissue hemoglobin contents were significantly increased by 53-66% in the high Ppv groups, compared with low vascular pressure controls, but there was no significant difference between High Ppv and Iso groups. Thus isoproterenol significantly attenuated vascular pressure-induced Kfc increases at moderate Ppv, possibly because of an endothelial effect, but it did not affect red cell extravasation at higher vascular pressures.