Effects of aging and dietary protein intake on uninephrectomized geriatric dogs

Thirty-one clinically normal Cocker Spaniels, Miniature Schnauzers, and Doberman Pinschers (28 female, 3 male) 7 to 8 years old were uninephrectomized (month -2) to increase the risk of renal damage associated with reduction of renal mass. Two diets, differing principally in protein concentration, were used to test the hypothesis that high dietary protein intake causes renal damage in aging dogs. For 2 months after uninephrectomy, all dogs were fed diet A (18% protein). After glomerular filtration rate (GFR) was measured (month 0), 16 dogs were assigned to group A and were fed diet A for an additional 48 months. The other 15 dogs were assigned to group B, and were fed diet B (34% protein) for the subsequent 48 months. At 6-month intervals, GFR and urine protein-to-creatinine ratio (UP/C) were determined. At 48 months, terminal studies were done, survivors were euthanatized, and tissues were examined. Of 16 dogs in group A, 10 survived, compared with 13 of 15 in group B. Among survivors, a significant difference in GFR was not found between groups A and B, and decrease in GFR was not evident with time in either group. At 48 months, oral administration of casein caused minor acute effects on GFR and renal plasma flow in dogs of groups A and B. The UP/C values increased significantly (P = 0.001) from baseline values, but the increase was not progressive. The UP/C values were not affected by diet. Some dogs in both groups developed UP/C > 1.0.(ABSTRACT TRUNCATED AT 250 WORDS)