Radiation nephropathy in young and adult rats.

The effects of bilateral kidney irradiation were compared in young and adult rats. During a 1 year period after a single dose of 0, 7.5, 10, 12.5, or 15 Gy on both kidneys, renal function (glomerular filtration rate and effective renal plasma flow), urine composition, and systolic blood pressure were measured periodically. The first changes after irradiation were observed in the glomerular filtration rate and urine osmolality. One month after 10, 12.5, and 15 Gy, glomerular filtration rate (GFR) and urine osmolality had declined below control values in the young rats. After this initial decline, renal function increased at control rate or even more during the third and fourth month after irradiation but decreased progressively thereafter. In the adult rats, GFR and urine osmolality started to decrease 3 months after 10, 12.5, and 15 Gy. A rise in systolic blood pressure and proteinuria started 2-3 months after 12.5 and 15 Gy in both age groups. Early changes in the glomerular filtration rate with a drop in urine osmolality in young rats, occurring during a period of rapid renal development indicated an irradiation-induced inhibition of glomerular and tubular development. Although renal function deteriorated at a later time in adult rats, dose-response relationships obtained in young and adult rats did not show significant differences.