Vascular permeability in the ears of rats after x-irradiation.

Late fibrosis in normal tissue is a complication which develops gradually after radiotherapy. It may be related to increase in vascular permeability induced by radiation. Plasma proteins leak into irradiated tissue where fibrinogen may be converted into fibrin which is gradually replaced by fibrous tissue. Vascular changes in the rat ear were investigated for six months after X-irradiation; Blood volume and vascular permeability were measured in vivo by monitoring the radioactivity in both irradiated and control ears after intravenous injection of phosphorus 32 labelled red cells and either iodinated (iodine 125) albumin or fibrinogen. After a single dose of 40 Gy there was an early increase in vascular permeability to both albumin and fibrinogen. After 20 Gy permeability to albumin was only increased during desquamation but extra-vascular fibrinogen accumulated at earlier times. Extravascular albumin was removed rapidly from irradiated ears, whereas some residual fibrinogen remained. Vascular permeability returned to normal but six weeks and showed no further changes up to six months after irradiation. Differences between the accumulation of extravascular albumin and fibrinogen at early times after irradiation could be due to some fibrinogen being fixed in the tissue. However, the rat ear showed no late changes comparable to the gradual development of late fibrosis seen in man.