The Focal Spread of Macromolecular Tracers in Vessel Walls: Frequency and Effect of Intima Compaction and Blood Pressure.

Atherosclerosis appears to begin when a transmural pressure (DeltaP)-driven water flow advects low-density lipoprotein cholesterol from the lumen into the subendothelial intima around rare, isolated endothelial cells with temporarily widened junctions. We compare frequencies of large-molecule leaks in the susceptible, large, high-pressure aorta, the rarely susceptible pulmonary artery and the immune inferior vena cava. The average horseradish peroxidase (HRP) leakage frequencies from 35 male Sprague Dawley rats are, respectively, 7.38+/-1.77, 3.34+/-0.87, 0.441+/-0.158 per 104 cells. Neither tracer circulation time nor acute blood pressure affects these numbers. Our group's earlier theoretical work explained historic HRP localized spot growth vs circulation time data with a water and macromolecular transport theory. Our local theory based on the idea that the intima compresses under DeltaP causing the endothelium to block IEL fenestrae, thereby lowering wall hydraulic conductivity Lp, clarified anomalous Lp data. Combining these theories, Chapter 3 predicts that only with initmal compaction do higher acute pressures mean smaller spots with shorter rise times. Our subsequent experiments verify these predictions. Although Huang et al.'s axisymmetric convection-diffusion transport theory predicts HRP concentration near localized leaks vs r, z and t, experimental spot size tests correspond to integrating these predictions through the tissue. A more stringent test would be to compare predictions with 3D HRP concentration profiles. Chapter 4 uses confocal microscopy and an HRP substrate with fluorescent reaction products to observe such profiles. Our theory can mimic these experiments, including the washing period before fixation and we successfully compare experiment with theory. Such comparison involves using 3D interpolation to calculate an optimally (Bremerman's algorithm) locate the coordinate origin and tilt angles of the axes for each data set. Aquaporins are ubiquitous water channel membrane protein. My labmates have found aquaporin1 in rat aortic endothelial cells and have shown their chemical blockage significantly lowers vessel wall hydraulic conductivity in a pressure-dependent manner. Our group believes blocking aquaporins shifts a larger fraction of the transmural DeltaP to the endothelium, thereby compressing the endothelium at lower DeltaP. We predict how, at low DeltaP, aquaporin blockage-induced intimal compression would affect HRP spot growth and confirm these predictions with rat experiments.