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Urea, Citrate and Orotate Excretions in Growing Rats Fed Amino Acid-deficient Diets^1,2,

Department of Animal Science, Cornell University, Ithaca, New York 14850

Male, weanling rats were fed a control purified amino acid diet or the same diet with lysine, phenylalanine, tryptophan, valine, or arginine omitted singly, or both arginine and lysine omitted. Blood urea reached three to four times that of control levels with all deficient diets. Urea excretion increased almost linearly with time during the first 3 days of amino acid deficiency. Rates of urea excretion on day 3 in decreasing order for various deficiencies were as follows: lysine and arginine combined > lysine > tryptophan = valine > phenylalanine = arginine. Urinary citrate was 26 and 21.8 times that of control values without arginine and 11.4 and 6.2 times that of control values without lysine on days 2 and 3, respectively. By day 8 citrate excretion had returned to control levels without lysine but not without arginine. Citrate excretion was unchanged with other deficiencies. Orotic acid excretion increased markedly only without arginine and slightly without tryptophan. A deficiency of arginine and lysine increased urea and citrate excretions to a greater extent than either deficiency alone. Two injections of arginine or homoarginine (0.50 mmole/injection) given at 12-hour intervals to rats fed no lysine and arginine for 3 days decreased citrate excretion immediately and on the following day. Urea excretion decreased with injected homoarginine, but not with arginine. Orotic acid excretion increased more than four times on the day of homoarginine injection compared with that of the preceding day. Arginine injection returned orotic acid excretion to nearly control levels within 24 hours. Urea degradation in the gastrointestinal tract was increased in animals fed amino acid-deficient diets.

KEY WORDS: • arginine • lysine • tryptophan • citrate • orotate • urea • amino acid deficiencies

¹ Present in part at Federation of American Socleties for Experimental Biology Meeting (1973) Proc. 32, 893. (Abstr.)

² Financial assistance was provided in part by USPHS Comparative Gastroenterology Training Grant no. IT01AM05684-02 and USPHS Training Grant no. ES00098.

³ Present address: U.S. Meat Animal Research Center, Clay Center, Nebr, 68933.

Manuscript received 1 June 1973.