Long-term vascular effects of ionizing radiations in the mouse: capillary blood flow

The comparative effects of total-body exposure to 60Co gamma rays or fission spectrum neutrons on subcutaneous capillary blood flow in the B6CF1 mouse have been estimated by measurement of xenon clearance after subcutaneous injection of 133Xe in a saline solution. These findings are important as an indicator of functional changes in the microvasculature that can then be related to structural changes observed both in vivo and with the electron microscope. The clearance of 133Xe from the subcutaneous injection site can be fitted to a single exponential. In unirradiated control mice, the mean halftime (T/sub 1/2/ = ln 2/lambda) in 4-month-old animals was 9.83 +- 0.72 min and ranged between 9.48 and 10.70 min during the first 12 months of observation (4 to 16 months of age). The halftime increased to 130 to 140% of the initial mean value during the second year, and then decreased to as low as 50% in very old animals. In mice irradiated at 4 months, the clearance halftime of 133Xe increased significantly 3 to 6 months after exposure to gamma rays or fission neutrons at dose levels well below the acutely lethal range (e.g., 268 gamma rad or 80 neutron rad). More severe injury levels, but still below the acutely lethal range, resulted in little change from mean control values. In all irradiated groups, however, clearance times were shorter at ages in excess of the mean survival time, suggesting a compensatory increase in capillary blood flow. Although capillary blood flow showed significant changes in relation quality and dose, the absence of a clear dose-response relationship precludes quantitative comparison of dose effectiveness for neutrons and gamma rays