Hydraulic conductivity of the endothelial and outer layers of the rabbit aorta

Pressure-driven fluid flow across the arterial wall was measured to determine wall hydraulic conductivity (Lp) before and after removal of the endothelium. The thoracic aortas of rabbits, anesthetized with Nembutal, were cannulated, perfused with oxygenated Ringer solution, and removed. With one cannula connected to a capillary manometer and the other closed, the manometer meniscus shift could be used as an indication of fluid loss through the wall plus vessel volume increase (creep). The latter effect, when measured, accounted for about one-fourth of the total volume displacement. The Lp given in cm/(s.cmH2O) +/- SD, was 3.30 +/- 0.96 x 10(-8). Another method employed continuous weighing of a closed aortic segment to obtain fluid loss, and yielded an Lp of 4.07 +/- 1.3 x 10(-8), and after mechanically removing the endothelium, the Lp became 7.73 +/- 2.8 x 10(-8). Using the above data, an Lp could be calculated for aortic endothelium of 8.6 x 10(-8). This suggests that about half the total transmural pressure drop occurs across the endothelium. Scanning electronmicrographs were used to check the condition of the endothelium.