Localization of aortic disease is associated with intrinsic differences in aortic structure.

PURPOSE: While localization of atherosclerosis and aneurysms to the infrarenal aorta has been attributed, in part, to hemodynamic factors, anatomic differences between the proximal and the distal aorta may also be important. Our purpose was to determine the changes in content and organization of major structural proteins (elastin and collagen) throughout the normal human aorta. METHODS: Biochemical analysis for desmosine-isodesmosine (elastin) and hydroxyproline (collagen) content was done by HPLC on complete 1-cm transverse rings removed from the ascending and descending thoracic aorta and abdominal supraceliac, suprarenal, and midinfrarenal aorta. Elastin and collagen content was normalized to lumenal surface area and compared by ANOVA: Light microscopy and optical micrometry were used to determine changes in intimal, medial, and adventitial thickness and number of elastin lamellae at each level. RESULTS: Both collagen/cm2 and elastin/cm2 decrease from the proximal to distal aorta. Collagen content did not differ among the three abdominal segments, but there was a 58% decrease in elastin between the suprarenal and the infrarenal aorta. The proportion of elastin and collagen does not differ throughout the aorta except in the infrarenal aorta where there is decreased elastin relative to collagen. CONCLUSION: Collagen and elastin in the distal aorta bear an increased load as compared to the proximal aorta. The infrarenal aorta differs biochemically and histologically from the remainder of the aorta. A decrease in infrarenal elastin without a corresponding decrease in collagen may effect the compliance and integrity of the distal aorta. These anatomic differences may be important in predisposing the infrarenal aorta to atherosclerosis and aneurysm formation.