Arginine - Nutrition
1. What is Arginine?
Arginine is an essential amino acid for dogs and cats. It is classified as a gluconeogenic amino acid and contains a positively charged nitrogen side chain that can be used as a binding site for other molecules. Dietary arginine is absorbed by a dibasic amino acid transporter in the small intestine (particularly the jejunum) and plasma arginine is actively reabsorbed in the proximal tubule of the kidney. Species that do not require dietary arginine (such as humans) are able to endogenously synthesise adequate amounts of this amino acid through the conversion of glutamate into ornithine; ornithine is ultimately converted into arginine in the urea cycle through the activity of pyrroline-5-carboxylate synthase and ornithine aminotransferase. Low activity these enzymes are found in dogs and cats. Dogs and cats have an absolute requirement for dietary arginine.
2. Why is it Important?
Arginine plays a critical role in the detoxification of ammonia, resulting from the turnover and breakdown of proteins. It is an important intermediate in the urea cycle which converts ammonia to urea. In the cats the arginine dietary protein in order to handle the increased need for detoxifying ammonia released from amino acid catabolism a. Cats are also highly sensitive to dietary arginine deficiency, feeding an arginine free diet to cats can result in hyperammonemia and death within a few hours.
3. Roles in the Body
Arginine is a structural component of proteins; serves as a key substrate for the detoxification of ammonia; stimulates the release of hormones, such as insulin, glucagon, and gastrin; and is a precursor to nitric oxide (NO), which is used as a cell signalling mediator.
4. Consequences of Arginine Deficiency
Puppies fed an arginine deficient diet containing adequate total protein will experience a decreased food intake and hyperammonemia resulting in vomiting and ptylism, with an increase in urinary orotic acid excretion and muscle tremors. There are also reports of puppies developing cataracts after being fed an arginine-free milk replacer. Feeding an arginine deficient diet to adult dogs results in decreased in food intake.
Feeding of an arginine deficient diet to kittens results in diarrhoea, weight loss, food refusal, ataxia, hyperammonemia, and urinary orotic aciduria. Feeding a diet that has no arginine but contains substantial levels of other amino acids can result in death within a few hours.
There are no studies on either acute or chronic toxicity related to feeding high doses of arginine to dogs and no reports of safe upper limits. Kittens fed purified diets containing arginine at 5-10 times above the requirement had a decrease in growth rate, but immediate adverse effects were not noted. Toxicity studies in adult cats are lacking.
6. Dietary Sources
Sufficient arginine is found in plant and animal protein sources, such as muscle meat, eggs, dairy protein (i.e., casein), cereal grains, and pulses (i.e., legumes).
7. Diagnosing Arginine Deficiency
Diagnosis of arginine deficiency is based on fasted plasma amino acids and the presence of urinary orotic acid.
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