The absorption of a mixture of amino acids by rat small intestine

1. The absorption of a mixture of amino acids by the small intestine has been studied in vitro with mucosal slices from rat jejunum. The mixture contained eighteen amino acids and was used at a concentration of 9.5 mM in the incubation medium. The uptake of fifteen of the amino acids was followed in each sample with the aid of an amino acid analyser.2. The endogenous amino acid content of the slices decreased during preparation and further substantial losses occurred when the slices were preincubated for 30 sec before the addition of the amino acid mixture to the incubation medium.3. When the slices were incubated with the amino acid mixture for 4.5 min all of the amino acid studied were accumulated to give concentration ratios of approximately 2.0.4. The amino acids were taken up rapidly by the tissue so that on average 82% of the amino acids absorbed in 4.5 min had already accumulated after one min of incubation.5. The data for individual amino acids revealed no obvious competition between the various amino acids, and the extent to which the various amino acids were accumulated by the tissue was proportional to their concentrations in the mixture.6. When the Na(+) in the incubation medium was replaced by Li(+), the slices accumulated all of the amino acids studied to concentrations significantly higher than those in the incubation medium. However, the concentration ratios obtained with the Li(+) medium were all lower than those obtained with the Na(+) medium and averaged slightly more than 1.5.7. When the Na(+) in the incubation medium was replaced by K(+) there was little amino acid accumulation, although concentration ratios significantly greater than one were achieved for aspartic acid, glycine, histidine and methionine.     

The effect of amino acids on the intestinal absorption of immunoglobulins in the neonatal rat

An in vitro preparation of 10-day-old rat intestine was used to examine the absorption of a number of amino acids and immunoglobulins. Evidence was obtained for the active absorption of alanine, leucine, methionine, histidine and lysine, but not for aspartic acid. A selective absorption of the homologous molecule was found in experiments where ¹³¹I-labelled rat and bovine IgG were presented to the ileum in 10-minute incubations. The greater uptake of rat IgG was unrelated to the relative rates of catabolism of the two molecules.

Although the uptake of rat IgG was unaffected by 100 mM concentrations of neutral and acidic amino acids, the basic amino acids arginine and lysine significantly stimulated uptake.

     

Effect of amino acids on sugar absorption

1. Sacs of everted mid-small intestine of the hamster have been used to study the effect of amino acids on sugar absorption.2. The sugars employed were D-glucose, D-galactose, 3-O-methyl-D-glucose, D-fucose, L-glucose, alpha-glucoheptose, L-fucose, D-mannose and L-sorbose. The amino acids were L- and D-histidine, L- and D-methionine, L- and D-alanine, L- and D-valine, L- and D-glutamic acid, L-leucine, L-proline, L-ornithine and L-aspartic acid.3. Actively absorbed amino acids considerably inhibit the transport of actively absorbed sugars. The results give support for the view that D-histidine and L-glucose are actively transferred. Passively absorbed amino acids and sugars are not involved.4. As L-glutamic and L-aspartic acids in the mucosal fluid have no inhibitory effect on D-glucose absorption, although mucosal fluid L-alanine is quite potent, the step at which the latter exerts its inhibitory action must be before that at which the intracellular transamination of L-glutamic and L-aspartic acids occurs. It would seem likely, therefore, that L-alanine interferes with the process by which epithelial cells capture and concentrate sugars at the luminal border.5. More than one active transfer system may exist for D-glucose.6. The influence of actively absorbed L-amino acids on D-glucose active transport seems to be in some way related to the efficiency with which the amino acids are themselves concentrated.7. Inhibition of D-glucose active absorption by an amino acid may be a simple test of an amino acid's participation in an active transport system.     

The effect of carotid occlusion on the rate of net fluid absorption in the small intestine of rats and cats

The effect on net intestinal fluid absorption of unloading the baroreceptors by bilateral carotid occlusion was studied in rats and cats. It was shown that net fluid uptake from the intestine increased 30–40% upon carotid occlusion. This effect was eliminated by cutting the splanchnic nerves (cats) or by severing the nerves surrounding the superior mesenteric artery (rats). In fact, these denervation procedures resulted in a decreased net fluid absorption upon carotid occlusion. Cutting the vagal nerves did not significantly influence the response to carotid occlusion. It is concluded that the arterial baroreceptors influence net fluid transport in the small intestine, a reflex compensatory mechanism that may be important in different hypotensive situations.     

Effects of amino acids on chloride transport in Aplysia intestine

This investigation was principally undertaken to examine the mechanism by which organic solutes (amino acids) stimulate chloride transport across the Aplysia californica intestine. Isolated intestine, mounted between identical oxygenated seawater solutions, maintained stable transmural potential differences (serosa negative) and short-circuit currents for several hours at 25 degrees C. The addition of glycine to the mucosal solution stimulated rapid sustained increases in these electrical characteristics. The change in short-circuit increased curvilinearly with increasing concentrations of mucosal glycine. Mucosal glycine stimulated transmural potential difference and short-circuit current after mucosal phlorizin had partially inhibited D-glucose stimulation of the electrical characteristics. Mucosal glycine enhanced the transmural electrical characteristics. Mucosal glycine enhanced the transmural electrical characteristics after serosal ouabain had abolished them. The major portion of the amino acid-induced short-circuit current was carried by a net, active, chloride transfer from mucosa to serosa as determined by flux measurements. These results suggest that the amino acid-induced effect on chloride transport is mediated by a common mucosal membrane carrier for both sodium and the amino acid.     

The effect of amino acids on unconditioned interoceptive reflexes

Summary The aim of this work was the study of the effect of amino acids on the unconditioned interoceptive reflexes. The work was conducted on fasting cats and on those which were fed in condition of urethane anesthesia. Neutralized solutions of glutamic acid, cysteine and alanine were injected intravenously in the 1 : 10^–3 concentration. The author studied the changes of the reflex reactions in response to the stimulation of duodenal mechanoreceptors, the chembreceptors of the perfused section of the small intestine, the baroreceptors of carotid sinus and in response to the electric stimulation of the central end of the femoral nerve. After the intravenous administration of amino acids to fasting animals a change of the blood pressure pressor reactions into depressor was noted, while in animals which were fed the depressor reactions changed into pressor. The pressor reflex to stimulation of the femoral nerve was depressed both in fasting cats and in those which were fed. In stimulation of the baroreceptors of carotid sinus in these conditions the reflexes did not follow any definite laws.Reactions in response to the stimulation of the chemoreceptors of the perfused portion of intestine did not change. Thus, the intravenous administration of amino acids has a definite effect on the character of the reflexes, mainly by changing the condition of the peripheral part of the reflex arc.Evidently, the change in the metabolic processes occurring in the receptive zones and the impulsation which is transmitted from the zone to the central nervous system are decisive in the mechanism of interoceptive reflexes.Presented by Active Member of the AMN SSSR V. N. Chernigovskii     

The effect of dietary amino acids on immune reactivity.

The plaque-forming cell response and serum antibody titres to sheep red blood cells (SRBC) were enhanced in mice fed diets moderately deficient in the amino acids phenylalanine-tyrosine. These diets sustained normal growth during a 4 week study period. More severe limitation of phenylalanine-tyrosine or multiple essential amino acid restriction gave rise to a slight increas in the delayed hypersensitivity reaction to SRBC. These latter diets usually limit growth; nevertheless the humoral immune response to SRBC was not significantly depressed except in the mice fed a diet (diet 7) with severe restriction of seven essential amino acids. These results suggest that dietary restriction may suppress the production or function of an inhibitory cell, such as a suppressor T cell, whilst not affecting the effector cell to the same degree.     

The effect of vitamin C on the absorption of glycine and chlorides by the intestine

Summary The effect of ascorbic acid on the regulation of absorption of glycine was studied in experiments on 3 dogs with chronic fistulae of the intestine and colon. It was established that ascorbic acid, administered in definite doses, improved absorption of glycine in the intestine and of sodium chloride in the colon. 32 and 22 are the optimal ratios of glycine and sodium chloride to the vitamin. In the presence of the above ratio absorption of glycine in the intestines increases by 24–28%, while absorption of chlorides in the colon increases by 18%.Presented by Active Member Acad. Med. Sci. USSR P. S. Kupalov     

The effect of certain amino acids on reproduction of encephalomyocarditis virus

Summary L-lysine in 1–4 mM concentration inhibits reproduction of encephalomyocarditis (EMC) virus in suspension of Krebs-2 mouse-ascites-tumour cells. L-lysine inhibits reproduction of EMC virus to a lower degree when it is added 2 hours after the beginning of incubation. The antiviral effect of l-lysine is partially or completely prevented by simultaneous addition of certain amino acids (l-leucine, l-isoleucine) to the culture medium. l-lysine does not inhibit EMC virus reproduction when l-leucine is added one hour after the beginning of incubation. When l-leucine is added 2–4 hours after the beginning of incubation, virus reproduction inhibited by l-lysine is restored with a longer lag period. l-lysine inhibits synthesis of virus-specific RNA as well as synthesis of proteins in infected and non-infected Krebs-2 cells. When l-lysine and 1-leucine are added together, no inhibition of protein synthesis and of virus-specific RNA synthesis occurs. l-leucine reduces the concentration of C¹⁴-lysine in the acid-soluble fraction of the cells. l-lysine accelerates the release of previously accumulated C¹⁴-leucine from the acid-soluble fraction of the cells into the incubation medium. It is suggested that the antiviral effect of l-lysine and reversion of this effect by other amino acids is associated with their competition for ways of active transport.