Radiation Damage and Subendothelial Repair to Rabbit Ear Chamber Microvasculature: An in Vivo and Histologic Study

The mechanism of X-radiation-induced vascular damage and a form of proliferative repair have been studied. Mature microvasculature of 23 modified Sandison-Clark rabbit ear chambers was irradiated with single doses of 250-keV X rays. The in vivo study included 16 chambers (16 animals) divided into seven dose groups ranging from 0 to 1600 rad. Serial intimal swellings appeared along the vessel wall in all irradiated chambers starting within 3-4 days. These swellings partially occluded the lumina and resulted in localized constrictions. High-magnification photomicrography in vivo and histological evaluation indicated that this morphological change is associated with fast postirradiation proliferation of subintimal cells forming cell aggregates. This proliferative activity is scored in vivo as the number of vascular intimal repair sites per millimeter of vessel length, and is plotted as a function of time in days following radiation exposure, with radiation dose included as a dependent parameter. The microvasculature of the chambers was monitored for 30 days. Three irradiated and 4 control chambers (5 animals) were sacrificed for histology on the 6th (1000 rad), 14th (700 rad), and 30th (250 rad) days following irradiation. Proliferation of the subintimal cells was observed in all irradiated chambers by analysis of serial sections. These findings indicate that there is a correlation between the endothelial injury and the formation of subintimal repair sites in the microvasculature.