The Interaction of Convection and Diffusion in the Transport of I-Albumin within the Media of the Rabbit Thoracic Aorta

The interaction of convection and diffusion in the transport of I-labeled albumin within the wall of rabbit thoracic aorta was studied in vessels excised at in vivo length. They were pressurized with a solution containing no tracer and immersed in a solution containing labeled albumin. The label then entered the wall tissue via the adventitia and had to diffuse against the convective flux which occurred from the lumen to the adventitia. Experiments were performed on intact and deendothelialized vessels pressurized to 70 and 180 mm Hg. At the end of each experiment the vessels were subjected to sequential frozen sectioning parallel to the lumenal surface. The radioactivity of the 20-/im-thick sections was determined and expressed as a tissue:labeled solution concentration ratio. Transmural profiles of these ratios were thus obtained. The steady state was found to be achieved by about 90 minutes. When the convection was enhanced by removal of the endothelium, the average ratios were lower than when the endothelium was intact, and the profile was much flatter. The results suggest that convection influenced macromolecular transport within the arterial wall, even in vessels with intact endothelium. (Circ Res 57: 856-863, 1985)