Studies on the effect of diet in experimental renal disease.

Modulation of renal function and growth by the quantity of dietary protein has long been recognised, but its influence upon the course of experimental renal disease only more recently appreciated. The studies described were designed to investigate the effect of different dietary proteins, casein and soya, in the modulation of renal function in the normal rat, and their effect upon the course of experimentally induced renal insufficiency in the subtotally nephrectomised rat. Short term feeding studies (6 weeks) of isonitrogenous (24% protein) casein and soya diets produced no difference in glomerular filtration rate (GFR) or effective renal plasma flow (ERPF) in normal rats. However, high protein feeding (48% casein) induced renal hypertrophy and elevations in GFR and ERPF. In contrast, long term feeding studies (18 weeks) of the casein diet resulted in elevated levels of GFR and ERPF compared to an isonitrogenous (24% protein) soya diet. Maintenance of subtotally nephrectomised rats upon soya protein diets resulted in marked amelioration of induced renal disease, in terms of mortality, proteinuria and renal histological damage, when compared to rats maintained upon isonitrogenous 12% and 24% casein diets. Analysis of body composition revealed the carcasses of subtotally nephrectomised rats to be composed of significantly less fat, and have a greater water content than normal animals. This reduction in body fat was proportional to the degree of renal dysfunction, rather than the dietary protein source. Plasma amino acids of subtotally nephrectomised rats fed casein and 24% soya diets were similar, but elevated levels of plasma non essential amino acids were found in rats fed 12% soya. Reduced serum lipid levels were found in both normal and subtotally nephrectomised rats fed soya diets. Potential mechanisms involved in the evolution of renal disease and the role of dietary proteins are discussed.