Macromolecular transport in heart valves. I. Studies of rat valves with horseradish peroxidase

Macromolecular transport in heart valves. 1. Studies of rat valves with horseradish peroxidase. Am J Physiol Heart Circ Physiol 292: H2664-H2670, 2007. First published February 2, 2007; doi: 10.1152/ajpheart.0 I 419.2006-The present study aims to experimentally elucidate subtle structural features of the rat valve leaflet and the related nature of macromolecular transport across its endothelium and in its subendothelial space, information necessary to construct a rational theoretical model that can explain observation. After intravenous injection of horseradish peroxidase (FIRP), we perfusion-fixed the aortic valve of normal Sprague-Dawley rats and found under light microscopy that FIRP leaked through the leallet s endothelium at very few localized brown spots, rather than uniformly. These spots grew nearly as rapidly with HRP circulation time before euthanasia as aortic spots, particularly when the time axis only included the time the valve was closed. These results Suggest that macromolecular transport in heart valves depends not only on the direction normal to, but also parallel to, the endothelial surface and that convection, as well as molecular diffusion, plays an important role in macromolecular transport in heart valves. Transmission electron microscopy of traverse leaflet sections after 4-min FIRP circulation showed a very thin ( similar to 150 unto, sparse layer immediately beneath the endothelium where the FIRP concentration was much higher than that in the matrix below it. Nievelstem-Post et al.'s (Nievelstein-Post P. Mottino G, Fogelman A. Frank J. Arterioscler Thromb 14: 1151-1161, 1994) ultrarapid freezing/rotary shadow etching of the normal rabbit valve's subendothefial space supports the existence of this very thin, very sparse "valvular SLibendothelial intiiria " in analo y to the vascular subendothelial intinia.