Mechanisms of acute injury in the gamma-irradiated chicken: effects of a protracted or a split-dose exposure on the fine structure of the microvasculature.

The effect of radiation dose and time, both during and between exposures, on ultrastructural changes in the microvasculature has been studied in the mesentery of the 3-week-old chicken. The following60 Co gamma-ray exposure groups were compared: (1) 1200 R, Single (15 minute) exposure (>70% mortality within 24 hours). Within three hours after exposure, endothelial as well as interstitial connective tissue cells were severely damaged. Lesions included dilated mitochondria and endoplasmic reticulum (ER) cisternae, cytoplasmic vacuolization, lysis, and necrosis. There were disruptions of the endothelial barrier, and thrombosis and occlusion of small vessels. (2) 700 R, Single (15 minute) exposure (<5% mortality within 24 hours). Patent endothelial junctions and perivascular accumulations of extravasated plasma were present, but little frank cell degeneration was seen. (3) 10,000 R, Single exposure protracted over 24 hours (10% mortality within 24 hours after completion of the exposure). Ultrastructural chang...