Responses of Rats to Urea and Related Substances The Use of a Spaced-Feeding Technique

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Abstract
Spaced feeding, the practice of feeding rats for only two hours per day, has been found to increase the growth-depressing action of several nitrogenous compounds. Dietary urea depressed growth in both spaced and orthodox experiments; 5% of urea fed two hours per day was as effective as 30% fed ad libitum. The depression in growth has been correlated with the rate of urea intake and the level of urea in the blood, and was not affected by the level or adequacy of the dietary protein. Spaced feeding increased the toxicity of L-leucine, diammonium citrate, ammonium carbonate, and 2,4-dinitrotoluene. Growth depressions by the ammonium salts varied directly with blood urea. This regimen lessened the toxicity of 3′-methyl-4-dimethylaminoazobenzene and ethanol but had little effect on relative growth rates when biotin, vitamin B12 and folic acid were omitted from the diet or when glycine or antibiotics were added. The procedure shows promise in measuring the biological value of small amounts of protein.

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