The influence of dietary protein, lipid, phosphorus and sodium on renal structure and function in geriatric dogs

Eight weeks after unilateral nephrectomy thirty-five geriatric Beagle bitches were randomly assigned to one of three diets: [high protein, high fat (HPHF containing 39% protein and 33% fat on a dry matter basis DM), high protein, low fat (HPLF containing 38% protein and 15% fat DM) or low protein, low fat (LPLF containing 20% protein and 16% fat DM)].; Health status was evaluated before and after uninephrectomy and then every 16 weeks for 4-years. Nitrogen balance studies were performed at the end of 4 years.; All dogs maintained or gained weight over 4 years. There were no differences among diet groups based on physical examination, or body weight and no clinically relevant differences in blood values. Nitrogen balance studies were not significantly different among diet groups. No diet group was in negative nitrogen balance. There were no apparent differences in incidence of illnesses or mortalities between diet groups. No adverse effects were associated with long term feedings of these diets.; Serial abdominal radiography and ultrasonography were used to evaluate renal compensatory hypertrophy. Hypertrophy occurred rapidly for 8–12 weeks post-nephrectomy, but continued slowly throughout the study. Despite hypertrophy, renal size remained within the normal ranges for adult dogs. Diet did not affect renal compensatory hypertrophy.; Serial evaluations of glomerular filtration rate (GFR) and permselectivity were made throughout the study. Histomorphometry and glomerulosclerosis scoring were performed on kidney tissue from the uninephrectomy, at midpoint, and at the end of the study. There were no significant differences in renal function between diet groups, and GFR remained relatively stable for 4 years. Mild glomerulosclerosis occurred over 4 years with no difference between diet groups. Proteinuria, increased significantly over time, with no difference between diet groups. Protein excretion values remained within the normal range. Canine renal aging does not occur to the extent reported in humans.; Renal cortical and medullary echogenicity was measured relative to hepatic and splenic echogenicity. Neither diet nor time affected relative renal echogenicity. Normal canine renal cortical echogenicity is less than or equal to that of the liver, and less than spleen. The renal medulla was hypoechoic compared to the cortex.