Effect of Steroid on Impaired Vascular Function Induced by Irradiation

Background and Objectives：Intracoronary irradiation has been proven to reduce restenosis following perc-utaneous transluminal coronary angioplasty, however late thrombosis is another recurring problem. We evaluated the sequential changes of vascular dysfunction and morphological changes according to the radiation dosage in rats. The effects of dexamethasone on these changes were also evaluated. Materials and Methods：Female Sprague-Dawley rats were randomized into 4 groups (n＝20, each group), and were irradiated with 0, 5, 10, 20 Gray (Gy). The rats were sacrificed at 1 hour, 1, 3 and 7 days after irradiation. The physiographic responses and morphologic changes of the arterial rings were evaluated. After the time- and dose-response relationship was determined, an additional 40 rats were pretreated with dexamethasone for 3 days and irradiated with 10 or 20 Gy to evaluate the effects of the dexamethasone. Results：5 Gy irradiation did not induce endothelial dys-function. 10 Gy irradiation induced an impairment of endothelium dependent relaxation (EDR) only 7days after irradiation. 20 Gy caused an impairment of EDR from the very time of irradiation, although endothelium independent relaxation (EIDR) was not affected irrespective of dose or time. On immuno-histochemistry of vWF, all irradiated arteries showed mild de-endothelialization in acute phase and subsequent re-endotheli-alization. However, after 20 Gy irradiation, re-endothelialization did not occur. With dexamethasone treatment,