Age dependence of radiation nephropathy in the rat

A higher incidence of radiation nephropathy is reported in pediatric than in adult patients. Preliminary experiments showed that juvenile rats had lower renal tolerance than adult rats. The experiments reported here were designed to determine the age at which tolerance changes and the magnitude of the change. Five- to 25-week-old rats were given bilateral kidney irradiation with 15-29 Gy X rays given in five fractions. Renal function was assessed 4 and 6 months after irradiation. Isoeffect doses for renal dysfunction were 15.5-17.5 Gy for rats irradiated at 5-8 weeks of age and 20.2-25.2 Gy for rats irradiated at 12+ weeks of age. At 23 Gy, rats irradiated at 5.5 weeks of age developed renal failure after 16 weeks; this increased to 21 weeks for irradiation at 7.5 weeks of age and to 27+ weeks for irradiation at 12-27 weeks of age. Renal tolerance increased steadily for irradiation at ages between 5-10 weeks, and maximum tolerance was reached by 12-15 weeks of age; a similar dependence on age at irradiation was found for bone marrow transplant nephropathy. The decrease in renal radiosensitivity with age may partially explain the increased incidence of radiation nephropathy in pediatric populations.