Metabolic nitrogen balance

Garza, C., Scrimshaw, N. S., and Young, V R (1977). Human protein requirements A long term metabolic nitrogen balance study in young men to evaluate the 1973 FAO/WHO safe level of egg protein intake. /. Nutr. 107,335-352. 

See also Urea Cycle Reactions, Urea, Uric Acid, The Nitrogen Cycle, Utilization of Ammonia, Metabolic Nitrogen Balance, Amino Acid Degradation, Ammonia Transport in the Body, Citric Acid Cycle, ATP as Free Energy Currency (from Chapter 12)... 

Also see DIGESTION AND ABSORPTION INBORN ERRORS OE METABOEISM METABOLISM NITROGEN BALANCE PROTEIN [S] and REEERENCE PROTEIN.)... 

Two amino acids—cysteine and tyrosine—can be synthesized in the body, but only from essential amino acid ptecutsots (cysteine from methionine and tyrosine from phenylalanine). The dietary intakes of cysteine and tytosine thus affect the requirements for methionine and phenylalanine. The remaining 11 amino acids in proteins are considered to be nonessential or dispensable, since they can be synthesized as long as there is enough total protein in the diet—ie, if one of these amino acids is omitted from the diet, nitrogen balance can stiU be maintained. Howevet, only three amino acids—alanine, aspartate, and glutamate—can be considered to be truly dispensable they ate synthesized from common metabolic intetmediates (pyruvate, ox-... 

Valine (Val or V) ((5)-2-amino-3-methyl-butanoic acid) is a nonpolar, neutral, aliphatic amino acid with the formula HOOCCH(NH2)CH(CH3)2. Along with Leu and He, Val is a branched-chain amino acid and is found in high concentrations in the muscles. Val is needed for muscle metabolism and coordination, tissue repair, and for the maintenance of proper nitrogen balance in the body. ° The steric hindrance present in Val and He (caused by branching) lowers the rate of coupling reactions, resulting in an increase in side reactions. ... 

A number of procedures used to determine protein quality involve bioassays. Bioassays require feeding live animals protein ingredients for a specified period of time, and then estimating the nutritive value of the protein. Two such assays are the rat-based protein efficiency ratio (PER) bioassay and the human nitrogen balance assay (Dimes et al., 1994). Animal feeding experiments require chemical analyses of both the dietary inputs and then the metabolic output of the animal (e.g., body composition analysis, fecal sample analysis, collection, and assay for urine) from which the efficiency of protein metabolism can be predicted as well as how the protein supports animal growth and cell maintenance. 

A person on this diet would be in negative nitrogen balance and could not sustain normal metabolism. 

The indication for administering BCAA in patients with hepatic encephalopathy to compensate amino-acid imbalance was proposed by J.E. Fischer et al. in 1974, and implemented parenterally. However, oral application of BCAA for an adequate treatment period also has beneficial effects on cirrhosis and HE (7.) improvement in protein tolerance and the nutritional condition, (2.) improvement in cerebral functions (II8, 122), probably due to an amelioration of liver function, (2.) stimulation of ammonia detoxification with a positive nitrogen balance (118), (4.) reduction in or normalization of AAA levels, and (5.) promotion of glutamine synthesis with a favourable effect on the cells of the immune system and on renal function. By means of BCAA, it was possible to prolong the survival time and delay the occurrence of liver failure in rats with CC -induced cirrhosis. (123, 126) However, there are diverging results, which need further clarification. In principle, the use of BCAA is considered to be a necessary form of supplementary treatment for catabolic metabolism in cirrhosis (124,125, 127, 128, 130-132), in (also latent) HE and after curative resection of hepatocellular carcinoma. (I2l) (s. p. 280)... 

The effects of injury and corticoid administration on protein metabolism differ significantly in animals. The content of liver nitrogen is increased by giving cortisone to rats but fracture of the femur does not have this effect in spite of increased levels of cortisol in the blood (M13). The administration of cortisone has a constant effect on nitrogen balance at all levels of nitrogen intake whereas the catabolic response to injury is reduced or even abolished by diminished protein intake and weight loss prior to injury (M12). 

Negative Nitrogen Balance if protein intake is insufficient or if the balance of amino acids is incorrect for synthetic needs, endogenous protein is metabolized to liberate free amino acids for synthesis of essential proteins. 

The prevention and treatment of severe metabolic acidosis in patients with kidney disease is also important to prevent the development of renal bone disease, fatigue, decreased exercise tolerance, reduced cardiac contractility, and increased ventricular irritability. Metabolic acidosis also appears to stimulate protein catabolism, which can contribute to a negative nitrogen balance and lower albumin concentrations, as well as cause growth retardation in children. Lower serum bicarbonate levels in peritoneal dialysis patients have also been associated with a higher hospitalization rate and longer hospital stays. Severe acidemia (blood pH <7.1 to 7.2) suppresses myocardial contractility, predisposes patients to cardiac arrhythmias, and may lead to a decrease in total peripheral vascular resistance and blood pressure, reduced hepatic blood flow, and impaired oxygen delivery. ... 

Major differences exist between the metabolic, fluid, and electrolyte management of patients with acute versus chronic kidney disease (CKD). For example, positive nitrogen balance is more difficult to achieve in patients with acute renal failure (ARF) due to the increased rate of protein catabolism. Additionally, patients with acute renal failure are more likely to develop hyperglycemia during nutritional support and frequently are dialyzed by modalities that are not used commonly for the patient with end-stage kidney disease (ESKD). Because of these differences, the nutritional management of patients with ARF is discussed separately. 

The main effect of these hormones is to increase the laying down of glycogen in the iiver. At the same time, when injected into an experimental animal they put it into negative nitrogen balance -that is, they increase the breakdown of proteins and amino acids. In general, they seem to operate at least partly so as to reverse or counterbalance the effects of insulin, so that, in a normal healthy animal or human, carbohydrate metabolism is controlled partly as the result of a tug-of-war between insulin on the one hand and the glucocorticoids on the other. 

Distinction between the effects of injury on protein metabolism and the effects of corticoid on protein metabolism has been made by Munro (M17, MIS) who has found a marked gain in liver nitrogen content following cortisone administration to the rat, but not after femur fracture. He also notes that cortisone has a constant action on nitrogen balance at all levels of protein intake whereas the effect of injury is obliterated by prior protein depletion. 

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