Urolithiasis in the Rat

A strain of rats, designated NMRI-D which has been derived from the Osborne-Mendel strain, has been found to be particularly susceptible to the formation of calcium citrate calculi in the urinary tract. These rats form many stones when fed a diet containing 15% of casein and 4% Hubbell, Mendel, Wakeman salt mixture with sucrose as the source of carbohydrate, but form no stones when the casein is increased to 30% at the expense of sucrose. Supplementation of the 15% casein diet with soybean protein also eliminated uroliths; however, gelatin supplementation was not efficacious. In another experiment the basal casein diet was enriched with a level of phosphate that would be contained in 15% of casein. Some reduction in the incidence of stones was observed but they were not eliminated. It is suggested that a complete protein is necessary for protection against stones. Considerably fewer calculi were formed when sucrose was replaced by dextrose or starch and none formed with replacement by whole wheat flour.