Radiation-Induced Alteration in Angiotensin Converting Enzyme Activity in Cultured Bovine Pulmonary Artery Endothelial Cells
Bovine pulmonary arterial endothelial cells (BPAE) were exposed to a single dose 0, 5, 10, 20 or 30 Gy. Angiotensin converting enzyme (ACE) activity was determined in confluent monolayers under first order reaction conditions at 6, 24, 48 and 96 hr after treatment using [3H]-benzoyl-Phe-Ala-Pro as substrate. Irradiation decreased the number of viable endothelial cells in a dose-and time-dependent manner beginning at 24 hr after 5 Gy and reaching a maximum effect (20% survival) at 96 hr after 30 Gy. Total amount of protein per monolayer decreased during the same intervals, whereas protein content per cell rose signifying a radiation-induced hypertrophy of viable cells. When expressed per million surviving cells, ACE activity increased in a time-and dose-dependent manner beginning at 24 hr after 5 Gy and reaching a maximum four-fold increase at 96 hr after 30 Gy.**These results suggest that although at the lowest radiation dose (5 Gy), the increase in ACE activity per cell compensated for the enzymatic activity lost due to cell death at higher doses (10, 20 and 30 Gy), the increase in ACE activity per cell could not keep up with decrease in number of viable endothelial cells leading to an overall decrease in total ACE activity per culture well.