Abstract
In 1919 1 and again in 1923 2 we reported data which led us to conclude that diets high in protein injure the kidneys of the rabbit; and we offered the hypothesis that the injury was caused by the products of the increased amino-acid metabolism. The work was criticized on two scores:(1) The rabbit is a poor test object for experiments of this type; (2) There was no assurance that the diets contained all of the essential accessory factors and the proper distribution of mineral constituents.
Our further work accordingly dealt with the effect of the intravenous injection of various amino-acids on the kidneys of dogs and with the feeding of properly constituted diets, whose protein content varied from 8 per cent to 75 per cent, to rats. The injection experiments 3 showed that the presence in the blood of certain amino-acids in excess of the normal is quickly followed by severe injury of the kidneys.
A preliminary report follows of the data obtained from feeding rats diets containing different amounts of protein.
The diets all contained 3 per cent cod liver oil, 4.5 per cent of the Osborne and Mendel salt mixture, 50 mg. dried yeast extract, lard, corn starch and protein. As the protein increased, the carbohydrate and finally the fat decreased.
Part of the animals represented in the table received casein, the others dried powdered beef as the protein. It is clear that the degree of injury is roughly proportional to the concentration of the protein and the duration of the feeding. Histological examination of the kidneys disclosed damage which did not occur before six months, and then only with the higher concentrations of protein.
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