Endothelial integrity at aortic ostial flow dividers

Previous investigators have examined the luninal surfaces of perfusion fixed rabbit aortas and reported endothelial damage about aortic ostial flow dividers. These changes have been considered to represent in vivo endothelial injury predisposing to atherosclerosis at these sites. Although standard pressure perfusion fixation techniques were used by these investigators, the fixed aortas were usually cut, bent open and pinned to flat surfaces before viewing. Such procedures distort the aortic media and could result in artifactual endothelial disruptions. We therefore studied the effect of post-fixation aortic manipulation on luminal surface morphology about aortic ostia. Rabbit aortas were fixed by perfusion in situ, while intra-aortic pressure was continuously monitored. When the aortas were opened by means of two parallel, lateral, longitudinal cuts, so that bending and pinning was avoided and normal vessel curvature was maintained, no endothelial disruption occurred about aortic ostia. When aortas were opened with one cut, bent open and pinned flat, ostial flow dividers were somewhat stretched and elongated and there was endothelial disruption in the form of spindle cell formation at the center portion of the flow dividers. Endothelial deformation due to bending during pinning probably occurs preferentially at the flow dividers because the media is thickest at this point. The greater deformability at the adjacent media and differences in compliance between media and intima results in stretching, bending and plication of the intima over the projecting flow divider. Studies attempting to relate endothelial changes to differences in shearing stress about ostia must take into account deformations introduced by post-fixation manipulation.