Sixty beagles were used to study the effects of exposure to 330 R60 Co γ radiation (bilateral, whole-body) at 2 days of age on renal functional and morphological development in the growing dog. A significant deficit in grams kidney per kilogram body weight was found in irradiated dogs at 50 days of age (P < 0.05), but not at 125 or 200 days of age. Glomerular filtration rate (GFR) per kilogram body weight and GFR per gram kidney were not significantly different between irradiated and nonirradiated dogs at 50, 125, or 200 days of age, but blood urea nitrogen (BUN) was significantly elevated in irradiated dogs throughout this period (P < 0.05). The fractional distribution of intracortical renal blood flow, as determined by radiolabeled microspheres, to the outermost cortex was found to be reduced in irradiated animals at all ages evaluated (P < 0.05). The fractional blood flow to the outermost renal cortex was negatively correlated with BUN in both irradiated (P < 0.05) and nonirradiated (P < 0.05) animals. Based on prior demonstrations of reductions in nephron numbers following similar irradiation, these data indicate increases in mean single nephron GFR and nephronal hypertrophy in the kidneys of the neonatally irradiated dog. The renal functional and morphological adaptations are sufficient to maintain adequate renal function in growing, neonatally irradiated dogs. The BUN elevations in irradiated dogs are believed to be related to changes in intracortical renal blood flow, rather than indicating renal insufficiency. The possible importance of the functional and morphological adaptations to the subsequent development of chronic renal failure in neonatally irradiated animals is discussed.

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