The independence of maximal intimal thickening from severity of balloon injury in the rabbit aorta

Endothelial injury induces intimal thickening, but whether more extensive i njury increases the extent of neointimal proliferation in the rabbit aorta is not well defined. We induced graded injury in the abdominal aortas of ra bbits and maximal intimal/medial (I/M) area and thickness ratios were calcu lated from aortic cross sections harvested 2 weeks after injury. The degree of injury was verified by blinded observers who graded the extent of disru ption of the internal elastic laminae. Intimal thickening was not significa ntly different after severe injury (mean maximal I/M area ratio 0.32 +/- 0. 02 [SE], n = 16) compared with moderate injury (0.23 +/- 0.02, n = 8, p = 0 .24), but was greater than that induced by mild injury (0.08 +/- 0.01, n = 7, p <0.0001). The ratio of the maximal I/M thickness was similar in all gr oups (I/M thickness ratio 0.68 +/- 0.04, 0.73 +/- 0.04, and 0.56 +/- 0.04 f or severe, moderate, and mild focal injury groups, respectively; p = 0.19). Thus, balloon injury of the rabbit aorta induces reproducible thickening o f the intima by 2 weeks. The maximal I/M area ratio is dependent on the ext ent of injury, while the maximal intimal thickening is independent.