Glutamine plasma concentration

Glutamine Glutamine is the most frequently discussed nutraceutical in the cUnical literature as it is an essential fuel for immune and other proliferating cells and the plasma concentration decreases in a number of clinical conditions (Table 18.5). Provision of glutamine (or a dipeptide that contains glutamine), either enterally or parenteraUy, has... 

Consideration of other plasma amino acids also informs the diagnosis of inborn errors of urea synthesis. The plasma concentrations of glutamine and alanine are often elevated in parallel with or prior to the ammonium concentration as they act as a nitrogen buffer. Plasma arginine concentrations are low since the only synthetic route for arginine in humans is via the urea cycle. In contrast, the arginine concentration is elevated in ARG-1 deficiency. Hyperornithinemia and homocitrullinuria are the characteristic features of the hyperammonemia, hyperornithinemia, and homocitrullinuria (HHH) syndrome caused by a defect in the ornithine transporter (ORNT-1). 

The glutamine formed in the liver is released into the systemic circulation. Through arterial blood, the brain is also supplied with ammonium (approximately 10% of the plasma concentration). Detoxification is effected via glutamine synthesis. The glutamine formed in the brain enters the blood circulation. In the muscles, ammonium... 

Because the hver metabohzes the aromatic amino acids (i.e., phenylalanine, tyrosine, and tryptophan), methionine, and glutamine, the plasma concentrations of these amino acids are elevated in cirrhotic patients. Plasma concentrations of the branched-chain amino acids (BCAAs) (i.e., valine, leucine, and isoleucine) often are depressed because these amino acids are metabohzed by skeletal muscle. This altered plasma aminogram contributes to the development of hepatic encephalopathy. 

The neutral amino acids alanine, serine, threonine, asparagine, glutamine, valine, leucine, isoleucine, phenylalanine, tyrosine, tryptophan, histidine and citrulline share a common transporter at the luminal border of the epithelial cells in the renal tubuli and the epithelial cells in the small intestine [16]. In Hartnup disorder an impairment of this transporter leads to hyperexcretion of these neutral amino acids and to intestinal malabsorption. Excretion of tryptophan metabolites kynurenine and N-methyl-nico-tinamide is reduced. Plasma concentrations of the affected amino acids may be low normal or reduced. The inheritance is autosomal recessive. The hph2-deficient mouse has been postulated as a model for Hartnup disorder [17]. Affected persons may be asymptomatic, while some demonstrate pellagra-like photodermatitis or cerebellar ataxia due to a nicotinamide deficiency and respond well to the administration of nicotinamide [16]. 

Prolonged strenuous exerdse is associated with a temporary inununodepression that affects macrophages, neutrophils, and lymphocytes. " The mechanisms involved are not fully established and appear to be multifactorial, including the actions of stress hormones (e g., catecholamines and cortisol), inhibition of macrophage and T-cell cytokine production, altered heat shock protein expression, increased oxidative stress, and a fall in the plasma concentration of glutamine. BCAAs are nitrogen... 

Walsh, N.P, Blannin, A.K., Clark, A.M., Cook, L., Robson, PJ., Gleeson, M., The effects of high-intensity intermittent exercise on the plasma concentrations of glutamine and organic acids, Eur J Appl Physiol, 77, 434, 1998. 

In plasma, the glutamine concentration is also the highest (c. 0.6 mmol/L). 

Glutamine, along with glucose, can stimulate insulin secretion by the endocrine pancreas. The significance of this is the regulation of the plasma glutamine concentration is not known. 

Figure 17.39 Effect of changes in glutamine levels in culture media on proliferation of human lymphocytes. The numbers represent the concentration of glutamine, in (xmol/L, in culture media. Note that both the maximum rate and the rate of response are decreased as the glutamine concentration in culture medium is decreased. The plasma glutamine level in normal humans is 600 (xmol/L.

Orotic acid in the diet (usually at a concentration of 1 per cent) can induce a deficiency of adenine and pyridine nucleotides in rat liver (but not in mouse or chick liver). The consequence is to inhibit secretion of lipoprotein into the blood, followed by the depression of plasma lipids, then in the accumulation of triglycerides and cholesterol in the liver (fatty liver) [141 — 161], This effect is not prevented by folic acid, vitamin B12, choline, methionine or inositol [141, 144], but can be prevented or rapidly reversed by the addition of a small amount of adenine to the diets [146, 147, 149, 152, 162]. The action of orotic acid can also be inhibited by calcium lactate in combination with lactose [163]. It was originally believed that the adenine deficiency produced by orotic acid was caused by an inhibition of the reaction of PRPP with glutamine in the de novo purine synthesis, since large amounts of PRPP are utilized for the conversion of orotic acid to uridine-5 -phosphate. However, incorporation studies of glycine-1- C in livers of orotic acid-fed rats revealed that the inhibition is caused rather by a depletion of the PRPP available for reaction with glutamine than by an effect on the condensation itself [160]. 

Alanine and Glutamine in the Blood Normal human blood plasma contains all the amino acids required for the synthesis of body proteins, but not in equal concentrations. Alanine and glutamine are present in much higher concentrations than any other amino acids. Suggest why. 

This metabolic activity is achieved by a turnover of amino acids and proteins that is as rapid as that of lipids and carbohydrates. In an adult human male, 400 g of body proteins is turned over each day. Of this, 50g is used to replace digestive enzymes (Sec. 15.2), and 6g to replace hemoglobin (Sec. 15.8). The concentration of free amino acids in plasma is small (total 3.2mmol L l, of which 25 percent is glutamine), but the turnover of 400g per day of protein is equivalent to the uptake, and release back into the plasma, of 4.6 moles of a-amino-N, so that the average lifetime of an amino... 

---