Microcirculatory effects of whole-body X-irradiation and radiomimetic procedures

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Abstract
Whole-body X-irradiation (WBR) was administered to young adult, unanesthetized rats. Terminal vascular beds of the exteriorized mesocecum of these rats (most of which had received relatively high doses of X-rays) were observed (under anesthesia) at selected periods between 1 hr and 48 days postirradiation. Thirteen experimental categories were utilized to determine the status of reactivity and of the microvascular barrier. These included topical application of epinephrine, norepinephrine, histamine, and Versene; and injection of heparin, cortisone, nitrogen mustard, bacterial endotoxin, and carbon. Results indicate that by the 3rd–4th day after WBR, response of terminal arterioles and precapillaries to epinephrine and norepinephrine are exaggerated and by the 2nd week, activity is up tenfold over threshold levels. With regard to venular and capillary walls, Versene had a dramatic disruptive effect. The character of the lesion suggests that it is due to an undermining and weakening of the basement membrane, and/or forces which hold the endothelial cells together. There is no evidence, however, that the endothelial cell has been damaged.