Effect of X irradiation and hyperthermia on vascular function in skin and muscle

Vascular change by the combined treatments of radiation and hyperthermia was studied. The legs of rats were irradiated with 2000 rad of X rays in a single dose and heated at 43.0 degrees C for 1 hr at various times after irradiation, and the blood flow and vascular volume in the skin and muscle were determined with 125I-microspheres and 51Cr-RBC methods, respectively. Irradiation alone caused an immediate increase in blood flow and vascular volume in skin and muscle followed by a second increase during 2-4 weeks postirradiation. Heating also caused an immediate and profound increase in blood flow and vascular volume. When tissues were irradiated first and heated the increase in blood flow and vascular volume was generally greater than that caused by irradiation or heat alone for about 4 weeks postirradiation. The combined effects were either additive or more than additive depending on the interval between the irradiation and heating during this period. Hyperthermia at 40 days postirradiation increased the blood flow and vascular volume only slightly above that of the irradiated control, indicating that the combined effect of irradiation and hyperthermia became less than additive. It was concluded that the thermosensitivity of irradiated blood vessels in skin and muscle for 3-4 weeks postirradiation was at least similar or greater than that of unirradiated controls. The thermosensitivity of vessels appeared to decline 40 days after irradiation.