Abstract
Nephropathy is an age-related spontaneous disease of most rat strains, and protein content of diet may affect the severity. The purpose of this study was to determine the effect of a 15% protein nonpurified diet on body weight and severity of nephropathy in comparison to a 23% protein NIH-07 diet. Groups of 25 male and 25 female Fischer-344 (F-344) rats, 6 wk of age, were fed the 23 or 15% protein diet ad libitum for 2 yr. Rats were weighed at 1–4-wk intervals, and mean body weights were determined. Water consumption measurements and urinalysis were done at approximately 3-mo intervals during the second year of the study. At the end of the 2-yr study, kidneys from all rats, including those that died or were euthanatized after the eightieth week of the study, were examined by light microscopy and graded for severity of nephropathy as grades 1–4 (minimal, mild, moderate, marked). Growth patterns and the maximum body weights attained by each sex fed the 23 or 15% protein diet were not significantly different. The severity of nephropathy in male rats was significantly higher when fed the 23% protein diet (2.8 moderate to marked) compared to the 15% protein diet (1.3 minimal to mild). The severity of nephropathy in female rats increased slightly when fed the 23% protein diet (1.5 minimal to mild) compared to the 15% protein diet (1.0 minimal). When the 23% protein diet group was compared to the 15% protein diet group, the 24-hr urine volume, proteinuria, and water consumption values were increased, especially during the last 3 mo of the study. Reduction of protein concentration in the diet from 23 to 15% decreased the protein consumption by30% and markedly decreased the severity of nephropathy, especially in male F-344 rats, without substantial changes in growth patterns and body weight gains.