Protein Sparing Action

It is well established that carbohydrates are utihzed in the synthesis of certain amino acids in the body and that the oxidation of amino acids is increased when the dietary source of carbohydrate or fat is inadequate to meet the caloric needs. Therefore, the differences between carbohydrates in promoting the efficient utilization of protein are of interest. 

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The protein-anabolic and protein-sparing actions of GH require the metabolic effects of insulin, glucagon, cortisol, and thyroid hormone in the unstressed individual. These actions depend on fine-tuned control of GH release, which is achieved mainly by substrate feedback to the hypothalamus (Figure 31-5). 

A more marked protein-sparing action has been reported for fructose as compared to lactose, glucose, sucrose, or dextrins (2, UU) While both glucose and fructose speed alcohol metabolism, fructose has the greater effect (13). 

Jones, H. M. The protein sparing action of utilisable carbohydrates in cultures of certain sugar fermenting organisms. Jour. Infectious Diseases, Vol. 19,... 

Protein Sparing Action Regulation of Fat Metabolism Provide Fiber Flavor... 

Amino acids arising from the mobilisation of body protein are utilised with the same efficiency as absorbed amino acids, and liveweight loss has a sparing action on metabolisable protein requirement equal to its protein content, i.e. 138 g/kg. An example of the calculation of the metabolisable protein requirement of a lactating cow is given in Box 16.4. 

Pyrimidines - The leukocytes of patients responding to l- -D-arabino-furanosylcytosine (ara-C) exhibited reduced DNA and elevated RNA and protein contents, whereas the normal bone marrow cells of these patients exhibited increased DNA, RNA, and protein contents. Despite extensive intracellular conversion of ara-C to nucleotides, only limited incorporation of the compounds into nucleic acids occurred. 2-Deoxy-cytidine reverses the effects of ara-C by inhibiting its phosphorylation, an anabolic step that must occur before it can inhibit DNA polymerase and, consequently, cell proliferation. Uridine exerts a sparing action on ara-C, and the effective level of this drug can be prolonged by coadministration of tetrahydrouridine, a potent inhibitor of deoxycytidyl-ate aminohydrolase. ... 

Carbohydrate has an antiketogenic action in that it inhibits the breakdown of fatty acids in the liver. It exerts a sparing action on protein by decreasing the rate of deamination of amino acids in the liver. 

Yoshida A, Moritoki K. Nitrogen sparing action of methionine and threonine in rats receiving a protein free diet. Nutr Rep Int 1974 9 159-168. 

The nutrient sparing effect of antibiotics may result from reduction or elimination of bacteria competing for consumed and available nutrients. It is also recognized that certain bacteria synthesize vitamins (qv), amino acids (qv), or proteins that may be utilized by the host animal. Support of this mode of action is found in the observed nutritional interactions with subtherapeutic use of antibiotics in animal feeds. Protein concentration and digestibiHty, and amino acid composition of consumed proteins may all influence the magnitude of response to feeding antibiotics. Positive effects appear to be largest... 

The net effects of these actions include enhanced growth due to protein synthesis enhanced availability of fatty acids for use by skeletal muscle as an energy source and glucose sparing for the brain, which can use only this nutrient molecule as a source of energy. 

Albumin is the most abundant protein in human and other animal plasma. It is estimated that up to 40% of the total albumin in humans is in circulation transporting essential nutrients, especially those that are sparingly soluble in aqueous-based plasma. For example, the fatty acids, which are important fuel molecules for the peripheral tissue, are distributed by albumin. In addition, albumin is the plasma transport protein for other substances including bilirubin, thyroxine, and steroid hormones. Also, many drugs including aspirin, sulfanilamides, clofibrate, and digitalis bind to albumin and are most likely carried to their sites of action by the protein. 

GH affects the uptake and oxidation of fuels in adipose tissue, muscle, and liver and indirectly inflnences energy metabolism through its actions on the islet cells of the pancreas. In snmmary, GH increases the availability of fatty acids, which are oxidized for energy. This and other effects of GH spare glucose and protein that is, GH indirectly decreases the oxidation of glucose and amino acids (Fig. 43.4). 

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