Responses of the carotid artery to acute, fractionated or chronic ionizing irradiation, and differences from the aorta

The circulatory system receives ionizing radiation at various dose rates. Given mounting epidemiological evidence of elevated radiation risks for diseases of the circulatory system (DCS), the International Commission on Radiological Protection recently recommended the first ever dose threshold for DCS. However, very little knowledge exists about whether radiation effects differ with dose rates and among tissues of the circulatory system. Here, we investigated the impact of dose rates in the carotid artery (CA) and compared it with the aorta. CA was obtained from mice irradiated with the same total dose that was delivered either acutely, 25 fractions, 100 fractions or chronically. CA underwent immunofluorescence and histochemistry staining. Irradiation led to vascular damage, inflammation and fibrosis in CA. The integrative analysis for 14 prelesional endpoints revealed that the magnitude of carotid changes was greater in 25 fractions, smaller in 100 fractions, and much smaller in chronic irradiation, compared with acute irradiation. Radiation responses of the aorta were qualitatively similar to, but quantitatively greater than those of CA. Irradiation causes sparing and enhancing dose protraction effects in a manner that is not a simple function of dose rate, and that radiosensitivity varies within the circulatory system.