Enzymatic Responses to Radiation in Cultured Vascular Endothelial and Smooth Muscle Cells

Confluent monolayers of bovine aortic endothelial and smooth muscle cells were exposed to 0-5.0 Gy of 60 Co γ rays. From 0 to 72 hr after irradiation, the monolayer and culture medium were analyzed for cell (nuclei) number, DNA and protein content, the activities of angiotensin converting enzyme (ACE), lactate dehydrogenase (LDH), and superozide dismutase (SOD), and LDH isoenzyme profile. Irradiated endothelial cells exhibited a time- and dose-dependent increase in cell detachment, decreased DNA and protein content and reduced ACE activity per attached cell, increased LDH and SOD activities per microgram of DNA, and increased LDH activity in the culture medium. The latter was accompanied by a shift from LDH 1 to LDH 4 and 5. The release of LDH activity, observed after 0.5 Gy, was the most sensitive endothelial response, and occurred independent of or preceding cell detachment. Vascular smooth muscle cells contained two to three times more SOD activity than did endothelial cells and exhibited no significant responses to 5.0 Gy.