Absorption Rates Of Glycine Research Articles

Absorption of free and peptide-linked glycine and phenylalanine in children with active celiac disease.

Using a marker perfusing technique, the jejunal absorption rates of glycine and phenylalanine from test solutions containing either the free amino acids or glycyl-phenylalanine (30 mM each) were studied in five children with active celiac disease and in three controls. Changes in plasma amino acid levels during intestinal loading were also investigated. Mean values of intestinal uptake rates (micromoles/min/20 cm segment) in patients and controls were found to be as follows: free glycine, 19.3 +/- 21.8 and 74.5 +/- 10.3; peptide-linked glycine, 45.0 +/- 12.4 and 110.7 +/- 20,1; free phenylalanine, 33.6 +/- 19.6 and 106.1 +/- 10.6; peptide-linked phenylalanine, 44.5 +/- 14.3 and 113.6 +/- 11.1, respectively. Thus, amino acid absorption is higher from peptide-linked glycine and phenylalanine, and the advantage of individual amino acid absorption from dipeptide seems to be maintained in the disease state. Changes of amino acid levels in plasma do not reflect impaired intestinal absorption because the levels of phenylalanine increased to the same extent in patients and in controls, and the increment of glycine was found to be higher in the patients group.

Effect of systemic bacterial infection on absorption rates of l-histidine and glycylglycine from the human jejunum in vivo

Jejunal absorption rates of L-histidine (from a 100 mmole/liter solution) and glycylglycine (from a 50 mmole/liter solution) were determined with a souble-lumen tube perfusion system in vivo in 12 Zambian African men; six had acute bacterial pneumonia (infection group) and six had no clinical evidence of a bacterial infection (control group). With this experimental design the mean rate of histidine absorption was significantly higher in the infection compared with the control group, but mean rates for glycine absorption from glycylglycine were not significantly different. During the glycylglycine infusions, the luminal disappearance rate of the intact peptide was significantly greater than the total glycine absorption rate. The correlation between individual histidine and glycylglycine absorption rates was significant. That is probably because after intracellular hydrolysis and efflux to the lumen, some glycylglycine is reabsorbed as free glycine by the amino-acid transfer mechanism, and the rate of that has previously been shown to be increased in subjects with systemic bacterial infections.

Intestinal absorption of glycine and glycyl-L-proline in the rat.

1. Absorption of [3H]glycine and [14C]-glycyl-L-proline at concentrations between 0-5 and 4 mmol/l was studied by perfusion in vivo of rat jejunal and ileal segments. Absorption was defined as net removal of radioisotope from the perfusate. Radioactivity assays and amino acid analyses were performed on perfusates and on mucosal tissue samples obtained from the perfused segments. 2. At the concentrations studied, absorption rates of glycine and glycylproline were proportional to concentration. Ileal rates were approximately 60% of jejunal rates. Glycylproline absorption was slightly faster than glycine absorption and was associated with the appearance in the perfusate of free glycine and proline in the ratio approximately 3:1. Intraluminal hydrolysis was insufficient to account for the amounts of free amino acids found and glycylproline hydrolase activity at the brush border is known to be minimal. 3. Glycylproline absorption apparently occurred by transport of the intact peptide followed by its intracellular hydrolysis. However, more than one-third of absorbed glycine and one-eighth of absorbed proline returned to the lumen as free amino acid. This reflux of glycine and proline was not proportional to their concentrations in the mucosa.

Comparison of Free Amino Acid and Dipeptide Absorption in the Jejunum of Sprue Patients

Utilizing a marker perfusion technique, jejunal absorption rates of free glycine and glycylglycine were investigated in five healthy human volunteers and 3 patients with an intestinal lesion resembling sprue. The absorption rates of both free glycine and glycylglycine were markedly reduced in the sprue patients, the reduction being more severe for free glycine than for glycylglycine (15-fold decrease versus 4-fold). In each patient, the glycine absorption rate was significantly greater from a test solution containing 50 mM glycylglycine than from a test solution containing a similar amount of glycine in the free form (100 mM). In 2 additional sprue patients the jejunal absorption rates of glycylglycine and glycyl-L-leucine were compared. There was no significant difference in the absorption rates of these two dipeptides, but both were markedly reduced. Our studies indicate that dipeptide is superior to free amino acid as a substrate for amino acid absorption even when the membrane transport is markedly reduced. Furthermore, the reduction in transport involves equally both a dipeptide with a poor potential (glycylglycine), as well as one with an excellent potential (glycylleucine) for hydrolysis by mucosal enzymes.

Effect of systemic infections on glycylglycine absorption rate from the human jejunum in vivo.

1. Using a double-lumen tube jejunal perfusion system, the rate of glycine absorption from a glycylglycine solution (50 mmol/l) was measured in three groups of Zambian African subjects: in fifteen subjects there was no evidence of an infection (normal group); in eleven there was acute bacterial pneumonia and five had a chronic systemic infection.2. Differences between the mean absorption rates for the three groups were not significant.3. Glycine absorption rate has been shown previously to be increased in subjects with acute bacterial pneumonia. The present result provides further evidence that glycine and glycylglycine use separate transfer mechanisms in man, and suggests that dipeptide absorption rate is influenced to a lesser extent than that for free amino acids by systemic stimuli.

Effect of glycylglycine and glycine on jejunal absorption rate of L-histidine in man in vivo.

1. Using a double-lumen tube jejunal perfusion system in vivo, the effects of glycylglycine and glycine on the jejunal transfer rate of L-histidine have been studied in a 30 cm jejunal segment, in six Zambian African men. Data on the effect of L-histidine on glycylglycine transfer rate have also been obtained. The solutions perfused in each subject contained (A) L-histidine (100 m-mole l.(-1)), (B) L-histidine (100 m-mole l.(-1)) and glycylglycine (50 m-mole l.(-1)), (C) glycylglycine (50 m-mole l.(-1)), and (D) L-histidine (100 m-mole l.(-1)) and glycine (100 m-mole l.(-1)).2. Whereas the presence of glycine in the perfusing fluid significantly impaired the absorption rate of L-histidine (P < 0.01), glycylglycine had no significant effect. The presence of L-histidine in the perfusing fluid had no significant effect on the rate of glycylglycine absorption. When compared with results for glycine absorption rate in twelve Zambian African subjects in another study, the presence of L-histidine produced a significant impairment in the rate of glycine absorption (P < 0.001).3. The results demonstrate a mutual inhibition between the rates of L-histidine and glycine absorption. The lack of a similar inhibition between L-histidine and glycylglycine is consistent with the concept of independent transfer mechanisms for amino acids and dipeptides in the human jejunum.

Increased glycine absorption rate associated with acute bacterial infections in man.

1. Glycine absorption rate from a 300 mm jejunal segment was determined in vivo in four Zambian African subjects with acute, and four with chronic, respiratory infections. Glycine solutions (100, 150 and 250 mmol/l) were perfused, by means of a double-lumen tube technique. The results were compared with those for four relatively normal Zambian African subjects (‘reference’ group) previously studied. The group with acute-infections had a significantly higher mean absorption rate than the reference or chronic-infection group.2. Glycine absorption results from a 100 mmol/l glycine solution in an additional twenty-four Zambian African subjects have also been analysed. When results for the thirty-six subjects were combined, those with acute bacterial infections had a significantly higher mean absorption rate than the normal subjects or those with chronic infections. For the twenty-one normal subjects there was a significant positive correlation between the individual absorption rates and serum total globulin and γ-globulin concentrations.3. It seems likely that the rapid catabolism of protein associated with infection is counteracted by an increase in amino acid absorption rate. In subjects on a low-protein diet that mechanism would be limited. The deterioration in nutritional status during infections in developing countries could therefore be partly explained by the present observation.

Intestinal transport of dipeptides in man: relative importance of hydrolysis and intact absorption.

A 30 cm segment of the duodenum, jejunum, or ileum of normal human volunteers was perfused, on separate occasions, with test solutions containing either glycylglycine, free glycine, glycylleucine, or equimolar amounts of free glycine and free leucine. Luminal fluid contained no hydrolytic activity against glycylglycine and minimal activity against glycylleucine. In each intestinal segment, amino acid absorption rates were significantly greater from the test solutions containing the same amount of amino acids in dipeptide than in free form(as high as 185% increase). Perfusion of each intestinal segment with a test solution containing the equimolar mixture of free glycine and free leucine always resulted in a greater leucine than glycine absorption rate. This preferential absorption of leucine, however, was either diminished (jejunum) or almost abolished (duodenum and ileum) when the glycylleucine solution instead of the equimolar mixture was presented to the intestinal mucosa. Among the three segments, the duodenum exhibited the least potential for the disappearance of dipeptides. The jejunal and ileal dipeptide disappearance rates were either similar for glycylleucine (94% vs. 92%) or slightly different for glycylglycine (92% vs. 79%). Despite lack of a remarkable difference in the disappearance rates, absorption rates of constituent amino acids were markedly greater in the jejunum than in the ileum. This reduced amino acid absorption was brought about by a greater accumulation of free amino acids in the lumen of the ileal segment (3 to 10-fold difference). Inhibition of free glycine absorption by leucine during the perfusion of the intestine with a test solution containing glycylglycine and leucine did not result in any greater concentration of free glycine in the lumen than when the glycylglycine test solution did not contain free leucine. Similarly, inhibition of free glycine and free leucine absorption by isoleucine was not accompanied by any remarkable alteration of absorption rates of the constituent amino acids of glycylleucine. The results of these studies suggest that: (a) dipeptide disappearance in the gut lumen is principally accomplished by intact absorption and not by hydrolysis; (b) intracellular hydrolysis of dipeptides is markedly greater in the ileum than in the jejunum, while dipeptide absorption rates are either similar or only slightly different in these two segments; (c) there is no appreciable hydrolysis of glycylglycine by the membrane-bound enzymes and only a small fraction of glycylleucine is hydrolyzed by these enzymes.

Effect of starvation on intestinal amino acid absorption.

ARTICLESEffect of starvation on intestinal amino acid absorptionM Steiner, and SJ GrayM SteinerSearch for more papers by this author, and SJ GraySearch for more papers by this authorPublished Online:01 Sep 1969https://doi.org/10.1152/ajplegacy.1969.217.3.747MoreSectionsPDF (1 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited BySpatial mRNA Expression and Response to Fasting and Refeeding of Neutral Amino Acid Transporters slc6a18 and slc6a19a in the Intestinal Epithelium of Mozambique tilapia13 March 2018 | Frontiers in Physiology, Vol. 9Regulation of Gut Function Varies with Life‐History Traits in Chuckwallas ( Sauromalus obesus : Iguanidae)Physiological and Biochemical Zoology, Vol. 78, No. 4Effect of starvation on neutral amino acid transport in isolated small-intestinal cells from guinea pigsPflügers Archiv, Vol. 423-423, No. 1-2Effect of early postnatal long-term fasting on the development of peptide hydrolysis in chicksComparative Biochemistry and Physiology Part A: Physiology, Vol. 101, No. 1Effect of starvation on the in vivo intestinal absorption of sugars and amino acids in young chickens (Gallus domesticus)26 September 2008 | Archives Internationales de Physiologie, de Biochimie et de Biophysique, Vol. 100, No. 2Changes in amino acid and glucose transport in brush-border membrane vesicles of hyperglycemic guinea-pig small intestineBiochimica et Biophysica Acta (BBA) - 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