The effect of potassium on the intestinal transport of glucose

The rate of absorption of glucose, galactose, and 3-0-methylglucose was studied in the rat's small intestine perfused in situ with isosmotic solutions containing these sugars and Na(2)SO(4) or K2SO(4). The presence of high [K(+)] in the lumen enhances absorption of glucose but not that of galactose or of 3-0-methylglucose. The potassium stimulation is apparent at higher glucose concentrations where primarily carrier-mediated diffusion is involved in the translocation. In this case potassium stimulates transport even if it is the only cation in the lumen. The potassium-stimulated intestine produces more glycogen with higher specific activity than the control gut. Lactic acid production by the intestine is markedly enhanced if the intestinal lumen is perfused with a solution containing glucose and high [K(+)]. It is concluded that potassium does not affect permeability or the specific sugar transport system of the gut, but enhances intracellular metabolic disappearance of glucose thereby creating a larger luminal intracellular concentration gradient which in turn enhances the rate of carrier-facilitated entry.

A note on perfusion with labelled compounds to determine intestinal absorption

An in vivo perfusion technique has been adapted for the measurement of intestinal absorption of labelled compounds. Salicylic acid, labelled with 14C, in solution with or without phenylephrine or caffeine, was perfused through the ligated and cannulated small intestine in situ of the rat. Absorption was estimated from the difference in count of the solutions entering the gut and the outflow which was sampled at 10 min intervals. Some 40–45% of the acid was found to be absorbed at each of three consecutive 10 min samplings. This was lower than, but consistent with, reported results derived by chemical assay. In the presence of the other two drugs the absorption of salicylic acid increased to 70%.

The influence of thyroid gland on amino acid accumulation and protein synthesis by rat small intestine in vitro

1. A method is described for measuring the accumulation of amino acids and also the extent to which the absorbed amino acids are incorporated into the tissue protein of rings of rat intestine in vitro.2. With this method rat jejunum was found to accumulate a mixture of amino acids to give a concentration in the tissue water which was 2-3 times that in the medium after 8 min incubation. More than 10% of the absorbed amino acids were found to be incorporated into protein.3. In surgically thyroidectomized animals there was no impairment of the capacity of the intestine to accumulate amino acids nor was there any loss of ability to incorporate these amino acids into protein. Similarly, treatment of the thyroidectomized animals with 3,5,3'-triiodothyronine (T(3)) did not produce any significant change either in the rate of accumulation or in the extent of the incorporation of the amino acids.4. The omission of glucose from the incubation medium was found to cause a large increase in the respiration of mucosal slices in the presence of the amino acid mixture. Thyroidectomy significantly reduced this high respiration rate. Treatment of thyroidectomized animals with T(3) restored the respiration to high value.

Amino acid accumulation and incorporation in rat intestine in vitro

1. Rings of rat jejunum incubated in vitro accumulate a mixture of amino acids at a rate of about 3 mumoles/cm. hr. The rate of incorporation of the accumulated amino acid into the tissue protein corresponds to a rate of synthesis of 50% of the protein of the whole wall in five days.2. Replacement of the Na(+) in the NaCl of the incubation medium by choline or by Li(+) did not prevent amino acid accumulation by the tissue. However, replacement of the Na(+) by K(+) prevented the accumulation.3. The accumulation of amino acids by rat jejunum in vitro proceeded at normal rates not only in the presence in the incubation medium of oxygen tensions below 10 Torr but also in the presence of 2,4-dinitrophenol. Reasons are given for supposing that the findings are compatible with the view that the energy upon which depend the processes of amino acid accumulation by the tissue could be derived from the movement of ions across cellular boundaries.4. The amino acid incorporation into the tissue proteins was reduced to one tenth of the control rate in the presence of 2,4-dinitrophenol or by hypoxia so that the processes of incorporation depend upon energy derived from oxidative metabolism. In the presence of oligomycin the tissue respiration was depressed but the amino acid incorporation into the tissue protein was not inhibited. The view that the amino acid incorporation may be able to function with energy intermediates other than ATP is discussed.

Calcium metabolism in normal and thyro-parathyroidectomized goats

1. The effects of thyro-parathyroidectomy on calcium metabolism in the goat have been investigated using stable calcium balance techniques and the isotopes (45)Ca, (47)Ca and (85)Sr.2. Thyro-parathyroidectomized goats, whether receiving supplementary thyroxine or not, are in negative calcium balance, whereas normal or thyroidectomized animals are in positive balance.3. Gastro-intestinal absorption of (45)Ca is less in thyro-parathyroidectomized goats, whether receiving supplementary thyroxine or not, than in either normal goats or thyroidectomized goats receiving thyroxine supplements.4. The rate of endogenous secretion of calcium into the gastro-intestinal tract is unchanged by either thyroidectomy or thyro-parathyroidectomy. Urinary excretion of calcium is also apparently unchanged.5. The bone calcium accretion rate is reduced to approximately the same extent in thyroidectomized and thyro-parathyroidectomized goats. Thyroxine supplements restore the bone accretion rate of both groups of animals to normal or greater than normal levels.6. The bone calcium resorption rate is greater in thyro-parathyroidectomized goats, whether receiving thyroxine supplements or not, than in either normal goats or thyroidectomized goats receiving thyroxine supplements.

Electron-microscope evidence for intramicrovillous fat absorption by the small intestinal epithelium of rats

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Transport of sugars and amino acids in the intestine: evidence for a common carrier

D-Galactose, L-arginine, and their respective actively transported analogs are partially competitive inhibitors of the active transport of neutral amino acids in the small intestine of hamsters. Since the aforesaid classes of compounds are all transported by similar, sodium-ion-dependent mechanisms and elicit countertransport of each other, all may share a common, polyfunctional carrier in which a series of separate binding sites, namely, one each for sugars, neutral amino acids, basic amino acids, and Na(+) are joined together, as in a mosaic.

The transmission of anti-Brucella abortus agglutinins across the gut in young rats

The anti- Brucella abortus titres of the sera of suckling rats fed 4 h previously with rabbit immune sera showed no correlation with the titres of the sera administered. This was due to them ultiplicity of the antibodies and their varying proportions in the immune sera, and their different rates of transm ission across the gut. The immune sera contained γ 1M - and γ 2 -complete agglutinins, but only the latter were transmitted in the rats. The gut exhibited selection between γ 2 -agglutinins from individual rabbits, but in all cases the antibodies appearing in the circulation were incomplete agglutinins. This qualitative difference in the antibodies before and after feeding was effected during transmission across the gut rather than after transmission in the circulation, and was attributed to a configurational change turning complete antibodies into the incomplete type rather than to a selective transfer of incomplete and exclusion of complete agglutinins. The incomplete antibodies appearing in the sera of fed rats partially reverted into the complete type on gel filtration and osmotic concentration, possibly due to the oxidation of disrupted disulfide bonds. It was not possible to relate the molecular size or electrophoretic mobilities of the agglutinins to their transmission.