Changes

==1. What is Histidine?==

==What is Histidine?==

Histidine is an essential amino acid for dogs and cats. It is characterised as a gluconeogenic amino acid and contains a positively charged imidazole side chain. Dietary histidine is absorbed by a neutral amino acid transporter in the small intestine (particularly the jejunum) and plasma histidine is actively reabsorbed in the proximal tubule of the kidney.

Histidine is an '''essential amino acid''' for dogs and cats. It is characterised as a gluconeogenic amino acid and contains a positively charged imidazole side chain. Dietary histidine is absorbed by a neutral amino acid transporter in the small intestine (particularly the jejunum) and plasma histidine is actively reabsorbed in the proximal tubule of the kidney.

==2. Why is it Important?==

==Why is it Important?==

Histidine is a structural component of proteins; it plays a key role in oxygen exchange, and is a precursor of biologically active compounds such as histamine and carnosine<ref>National Research Council (NRC). Protein and Amino Acids. In Nutrient Requirements for Dogs and Cats. 2006 Washington, DC: National Academies Press p. 122-123.</ref>.

Histidine is a '''structural component of proteins; it plays a key role in oxygen exchange''', and is a precursor of biologically active compounds such as histamine and carnosine<ref>National Research Council (NRC). Protein and Amino Acids. In Nutrient Requirements for Dogs and Cats. 2006 Washington, DC: National Academies Press p. 122-123.</ref>.

==3. Roles in the Body==

==Roles in the Body==

Histidine is present at high concentrations in haemoglobin; the positive charge on the imidazole side chain of this amino acid promotes oxygen exchange in the lungs and other tissues<ref>Cianciaruso B, et al. Histidine, an essential amino acid for adult dogs. J Nutr 1981;111:1074-1084.</ref>.

Histidine is present at high concentrations in haemoglobin; the positive charge on the imidazole side chain of this amino acid promotes oxygen exchange in the lungs and other tissues<ref>Cianciaruso B, et al. Histidine, an essential amino acid for adult dogs. J Nutr 1981;111:1074-1084.</ref>.

Histamine a neuro-active compound is formed from the decarboxylation of histidine, and plays a role in immune function and vasodilation. Carnosine is a histidine derived dipeptide that acts as a cellular antioxidant and copper and zinc chelator within mammalian cells<ref>Boldyrev AA, et al. Physiology and pathophysiology of carnosine. Physiol Rev 2013;93:1803-1845.</ref>.

Histamine a neuro-active compound is formed from the decarboxylation of histidine, and plays a role in immune function and vasodilation. Carnosine is a histidine derived dipeptide that acts as a cellular antioxidant and copper and zinc chelator within mammalian cells<ref>Boldyrev AA, et al. Physiology and pathophysiology of carnosine. Physiol Rev 2013;93:1803-1845.</ref>.

==4. Consequences of Histidine Deficiency==

==Consequences of Histidine Deficiency==

====Dogs:====  

====Dogs:====  

Feeding of a histidine deficient diet to kittens results in weight loss, decreased serum albumin and haemoglobin concentrations, and development of cataracts<ref>Quam DD, et al. Histidine requirements for growing kittens for growth, haematopoesis and prevention of cataracts. Br J Nutr 1987;58:521-532.</ref><ref name="Taylor">Taylor TP, et al. Optimizing the pattern of essential amino acids as the sole source of dietary nitrogen supports near maximal growth in kittens. J Nutr 1996;126:2243-2252.</ref>.

Feeding of a histidine deficient diet to kittens results in weight loss, decreased serum albumin and haemoglobin concentrations, and development of cataracts<ref>Quam DD, et al. Histidine requirements for growing kittens for growth, haematopoesis and prevention of cataracts. Br J Nutr 1987;58:521-532.</ref><ref name="Taylor">Taylor TP, et al. Optimizing the pattern of essential amino acids as the sole source of dietary nitrogen supports near maximal growth in kittens. J Nutr 1996;126:2243-2252.</ref>.

==5. Toxicity==

==Toxicity==

There are no studies on either acute or chronic toxicity related to feeding high doses of histidine to dogs and no reports of safe upper limits. Kittens fed purified diets containing histidine above the requirement had no adverse effects<ref name="Taylor"/>, but toxicity studies in adult cats are lacking.

There are no studies on either acute or chronic toxicity related to feeding high doses of histidine to dogs and no reports of safe upper limits. Kittens fed purified diets containing histidine above the requirement had no adverse effects<ref name="Taylor"/>, but toxicity studies in adult cats are lacking.

==6. Dietary Sources==

==Dietary Sources==

Sufficient histidine 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).

Sufficient histidine 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 Histidine Deficiency==

==Diagnosing Histidine Deficiency==

Diagnosis of histidine deficiency is based on fasted plasma amino acids and the presence of hypoalbuminemia and low serum haemoglobin concentration.

Diagnosis of histidine deficiency is based on fasted plasma amino acids and the presence of hypoalbuminemia and low serum haemoglobin concentration.