Ionizing Radiation Enhances Activity of Angiotensin-Converting Enzyme in Rat Aorta

We analyzed changes in angiotensin-converting enzyme activity in rat aorta at the early terms after irradiation in doses equal to one fraction dose used in tumor radiotherapy. Male Wistar rats were exposed to whole body or local (chest) X-ray irradiation (200 kV, 1-7.5 Gy). The activity of the enzyme in aorta segments was measured in 1-48 h after irradiation by hydrolysis of hippuryl-histidine-leucine. Activity of angiotensin-converting enzyme in rat aorta was increased 1-24 h after whole body irradiation in a dose of 2.5 Gy with a peak in 2 h after exposure. After local exposure, enzyme activity also increased in 2 h, but returned to the control level in 24 h. In 2 h after whole-body irradiation in doses >2.5 Gy, the increase in enzyme activity was less pronounced and after exposure to 7.5 Gy, it did not differ from the control. During local exposure, the effect did not decrease with increasing the irradiation dose. The fraction of blood monocytes adherent to plastic in rats subjected to whole body irradiation decreases with increasing the dose. In rats subjected to local irradiation in a dose of 7.5 Gy, monocyte adhesion to plastic did not differ from the control. These data suggest that the increase in activity of angiotensin-converting enzyme in the aorta after irradiation is determined by monocyte adhesion to the endothelium; the decrease in this effects with increasing the dose can be explained by radiation damage of monocytes.