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Plasma Ammonia, Plasma, Brain and Liver Amino Acids and Urea Cycle Enzyme Activities in Rats Fed Ammonium Acetate¹

Department of Physiological Sciences and Food Intake Laboratory, School of Veterinary Medicine, University of California, Davis, CA 95616

Male Sprague-Dawley rats were trained to eat a 6% casein diet within a 3-h period each day. They were then fed a 6% casein diet for 10–16 d before they were fed either the same 6% casein diet or the 6% casein diet supplemented with 15% ammonium acetate for 1 or 7 d. During the absorptive period, plasma ammonia, plasma amino acids and brain amino acids were measured on d 1 and d 7 after feeding ammonium acetate. Food intake of rats fed 15% ammonium acetate was depressed on d 1 and increased to approximately 75% of the intake of the 6% casein-fed group by d 7. On d 1 plasma ammonia of the rats fed 5% ammonium acetate was 101 µM as compared to 56 µM for the rats fed 6% casein (P < 0.05). On d 7, plasma ammonia of the rats fed 15% ammonium acetate was 240 µM (P < 0.05) as compared to 44 µM for the rats fed 6% casein. In rats fed 15% ammonium acetate, after 7 d ornithine transcarbamylase and arginase activities were higher and argininosuccinate synthetase activity was lower (P < 0.05) while carbamyl phosphate synthetase activity tended to be higher than that of rats fed 6% casein. The results suggest that rats adapt to ingestion of 15% ammonium acetate by some unknown neural mechanism rather than by increases in all urea cycle enzyme activities. Feeding ammonium acetate causes changes in plasma, brain and liver amino acid concentrations.

KEY WORDS: • casein • caloric intake • ammonium acetate • plasma amino acids • plasma ammonia • brain amino acids • liver amino acids • urea cycle enzymes

¹ This paper was supported in part by NIH grants DK 13252 and AM 07355.

Manuscript received 26 May 1988. Revision accepted 20 October 1988.

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