The time course of elastin fiber degeneration in a rat aneurysm model

Previous findings vary regarding the timing and cause of elastin fiber dege neration in the elastase-induced rat abdominal aortic aneurysm model. We ex amined the timing and cause of elastin fiber degeneration after elastase in fusion using two different elastase infusion times. Twenty-four Sprague-Daw ley rats were divided into two groups. The infrarenal abdominal aorta was i nfused with 15U of elastase for 15 min (n = 12, 15-min infusion group) or 3 0 min (n 12, 30-min infusion group). In each group, three rats were killed immediately and 1, 3, and 7 days after infusion, and then the aortas were e xcised for a histologic examination. Elastin fibers did not stain, even imm ediately after elastase infusion, in the 30-min infusion group. The degener ation of elastin fibers did not progress in the 15-min infusion group durin g the period of observation. Inflammatory cells infiltrated mainly to the a dventitia near regions where the degeneration of elastin fibers spread tota lly through the aortic media. Elastin fibers degenerate immediately after e lastase infusion and thus seem to degenerate not due to endogenous proteina ses that are produced by the infiltrating cells, but due to the exogenously infused elastase itself. Inflammatory cell infiltration was thus found to he a result of the degeneration of elastin fibers in this model.