Vascular permeability and late radiation fibrosis in mouse lung

It has been suggested that fibrosis which developed after irradiation is caused by increases in vascular permeability. Plasma proteins leak into irradiated tissue where fibrinogen may be converted into fibrin which is gradually replaced by fibrous tissue. Vascular and fibrotic changes in mouse lung were investigated after X irradiation of the right hemithorax. Blood volume and accumulation of extravascular proteins were measured using indium (111In)-labeled red cells, iodinated (131I) albumin, and iodinated (125I) fibrinogen. During the first few months after X rays, lung blood volume decreased to a plateau which depended on radiation dose (10-25 Gy). Small increases in extravascular albumin and fibrinogen occurred at 1-12 weeks after 10-25 Gy. Hydroxyproline per gram of dry irradiated lung was increased at 18 weeks after 15-25 Gy. Support for the hypothesis was that hydroxyproline per gram only increased after X-ray doses which caused marked extravasation of protein. There was no evidence, however, for deposition of 125I-fibrin or for a gradual increase in fibrosis corresponding to the prolonged excess of extravascular protein