Histological study of the effects of extensive freeze injury on the rabbit aorta

ABSTRACT

Cryopreservation of blood vessels has become one of the key techniques to make up the limited sources of fresh blood vessels. But cryopreservation methods do not adequately preserve complex natural or engineered multicellular tisses. When lesions are produced by localized freezing of the aorta, necrosis is present throughout the full thickness of the tunica media of tunica media as well as in the endothelium. The response of the vessel wall varies according to the extent of endothelial denudation and the period of freeze injury. From this point of view, this study was designed to investigate the histological effects of extensive freeze injury on the rabbit aorta. The abdominal aorta of twenty-five adult male rabbits were used in this study. Five normal adult male rabbits were used as a control [group I]. The remaining twenty rabbit aorta were exposed to extensive freeze injury by a 12-mm aluminium bar, cooled down to the temperature of liquid nitrogen and placed on the exterior of the abdominal aorta [infrarenal segment] for I min. Freeze injury was done at 1, 3, 14 days and one month [5 rabbits / time point], corresponding to groups II, III, IV, V respectively, the aortae were excised, fixed by buffered formol saline 10%, paraffin sections were prepared and stained by haematoxylin and eosin [H. and E.] to demonestrate the general architecture of the aorta, orceinfor elastic fibers demonstration in the wall of the aorta and masson's trichrome to illustrate the collagen fibers and smooth muscle cells [SMC] in the whole aortic wall. Group II showed injured surface with desquamated denuded endothelium covered with blood elements in a single layer. The internal elastic fibers were damaged at injury site. Group III showed regenerating endothelium at the edge of the injury zone. Proliferating intimal cells was observed. Group IV showed thickened and elevated intima at the injury zone with migrating smooth muscle cells from the media to the intima. Smooth muscle cells populated the subendothelial space of the injured zone under the regenerated endothelium. Group V showed the tunica media had an area of smooth muscle cells destruction with cellular debris and homogenous smooth degeneration. The intima showed full restoration of endothelial monolayer in the zone of injury. After extensive freeze injury, complete re-endothelialization of the denuded surface and SMC regeneration in the subendothelial space occured, resulting in endothelial myointimal thickening. On the other hand, irreversible changes in the smooth muscle cells of the tunica media were noticed