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G Wiseman

Publications and source records attributed to G Wiseman.

26 records · Page 2Linked to original sources
PubMed1968

Active transport of L-glucose by isolated small intestine of the dietary-restricted rat.

1. The effect of semistarvation and complete starvation (sufficient to produce a loss of about 32 and 25% respectively of initial body weight) on the active transport of L-glucose has been studied by the use of sacs of everted mid-small intestine of rats. The animals were allowed free access to water.2. Sacs from animals on a restricted diet transported L-glucose against its concentration gradient, but sacs from fully fed rats did not. Even when sacs from fully fed rats were distended sufficiently to cause them to lose serosal volume, the L-glucose concentration in the final serosal fluid was never greater than that in the final mucosal fluid.3. The L-glucose active transport was independent of net water movement, needed oxygen, was not demonstrable at 27 degrees C, and required Na ions at a concentration of 83 mM or greater. It could be completely inhibited by 10(-6)M phlorrhizin, or 10 mM L-histidine, or 1.39 mM D-glucose. Phlorrhizin at a concentration of 10(-8)M reduced, but did not prevent, L-glucose active transport.4. It seems probable that L-glucose active transport is mediated by the mechanism that actively transports D-glucose.5. Un-incubated mid-small intestine of fully fed rats contained 37.8 mg D-glucose/100 g wet wt. of tissue, whereas semistarved intestine had only 10.8 mg D-glucose/100 g. The lack of demonstrable active transport of L-glucose by normal intestine may possibly have been caused, at least in part, by inhibition of the process by endogenous D-glucose.6. There appeared to be no metabolism of L-glucose by rat intestine, nor conversion to the D-form.7. The hypothesis that sugars require the D-pyranose ring structure for active absorption is no longer tenable.

Animals↗
PubMed1967

Further studies on intestinal active transport during semistarvation.

1. The effect of semistarvation (sufficient to produce a loss of 18-28% of initial body weight) on the active transport of D-glucose and L-histidine by the rat, the guinea-pig and the golden hamster has been investigated by the use of sacs of everted small intestine (from upper jejunum to lower ileum).2. In the rat and the guinea-pig the dietary restriction resulted in increased active transport in all regions of the small intestine. In contrast, it caused no alteration in active transport in the hamster.3. The response in the rat was most impressive in the middle-to-lower ileum during D-glucose uptake. Whereas normal sacs from this area appeared unable to move the sugar against its concentration gradient, sacs from semistarved rats did so quite well.4. Although there was a considerable loss (24-29%) of intestinal dry weight in all three species when the food intake was reduced, shortening of the small intestine was not detectable in the guinea-pig or the hamster and was present to only a minor extent in the rat.5. Evidence is presented indicating that the enhanced active transport is not merely a reflexion of the thinning of the intestinal wall and that it occurs during complete as well as in partial starvation.

Animals↗
PubMed1966

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.

Alanine↗