RESPONSE OF MESENTERIC BLOOD-VESSELS TO IRRADIATION

The response of mouse blood vessels to radiation has been studied by locally irradiating mesenteric vessels, in an exteriorized segment, using a strontium-90 β applicator. Four different assays of damage were made when the animals were sacrificed from 6 weeks to 18 months after irradiation. In all studies sham-irradiated animals were compared with those receiving 20, 30, and 45 Gy. Vein diameter was studied by direct observation, vascular volume and permeability by isotope techniques, and the cellularity of the arterioles from histological sections. Within 3 months changes were seen in all these parameters, with a gradual recovery toward normal by 12 months, and a second phase of damage appearing at 18 months. The time course changes in vascular permeability appeared to match the loss of endothelial cells lining the arterioles, but there was a significant correlation only at 6 weeks. Fibrosis was not seen before 12 months, but at 18 months the vessel walls were fibrosed, sclerotic, and occasionally the lumen was occluded. At no time was any change in the dependent ileum seen. The blood supply to this tissue was maintained in spite of the severe radiation damage in the vessels.