Radiosensitivity of vascular tissue. II. Differential radiosensitivity of aortic cells in vitro

The cellular outgrowths from three layers of rabbit and monkey aorta were used as primary cultures. Irradiation of the tissue fragments at the time of explanation resulted in a reduction in outgrowth of 50% with a dose of 200 rad, and in a reduction of over 90% with doses of 300 rad and above. When comparable cultures were irradiated after 2 months in vitro as a mature actively metabolizing but slowly proliferating cell population, radioresistance was increased. Subcultures of medial smooth muscle cells irradiated during their logarithmic growth phase showed a linear dose response in the cell number parameter up to 150 rad. A dose of 250 rad resulted in complete flattening of the growth curve, with a reduction in labeling index, after a 3-hr terminal [3H]TdR pulse. On the other hand, the labeling index indicated some recovery 3 days after irradiation in cultures receiving less than 250 rad. Under the same experimental conditions, cells derived from the intima of the same aorta showed no recovery when increase in cell numbers over time, or the number of labeled cells per area, were used as parameters. Cells derived from adventitia showed a relative increase in the number of labeled cells per area 4 and 7 days after irradiation following an initial decrease on Day 1.