Effects of fasting and semistarvation on the kinetics of active and passive sugar absorption across the small intestine in vivo.

Abstract

SUMMARY1. The effects of dietary restriction on the kinetics of absorption in vivo of glucose, galactose and a-methyl glucoside were assessed by electrical and chemical methods in the rat jejunum.2. The 'apparent Ki', maximum absorption or Vmax (jc-mole/ 1O cm.15 min) and maximum potential difference (p.d.max) were obtained for the jejunal electrogenic active transfer mechanism from the transfer p.d.s and the chemical absorption data corrected for diffusion using various graphical kinetic plots.3. Fasting for 3 days greatly decreased the 'apparent K.s', obtained from electrical or chemical data, for all the sugars but had no effect on those for L-valine or L-methionine. Semistarvation caused a less pronounced reduction of the 'apparent Kms' for the sugars. The dietaryinduced change in 'apparent K.' for glucose was also observed in the fasted hamster. One interpretation of these changes is that the affinity of the carriers for sugars increases during dietary restriction; the greater the level of restriction the greater the increase.4. Fasting and semistarvation caused large reductions in the Vmax. These reductions were correlated with a reduced enterocyte population estimated by changes in enterocyte column size.5. The reduction in the VmaX for galactose was mainly accounted for by the decrease in enterocyte population. In the case of glucose, other factors such as reduced enterocyte metabolism or changes in the carriers must be involved to explain the discrepancy between the large decrease in Vmax and the enterocyte column size.6. Fasting and semi-starvation had complex, differential actions on the * Present address: Department of Physiology, Royal Free Hospital School of Medicine, Hunter Street, London, WC1N IBP. E. S. DEBNAM AND R. J. LEVIN p.d.max for glucose, galactose and x-methyl glucoside. These changes did not correlate with those observed in the Vmax measured chemically. 7. A standard diet obtained from two commercial sources was found to differ greatly in its effect on the electrogenic transfer system for cx-methyl glucoside but had no effect on those for galactose and glucose.

Augmentation of neutral sodium chloride absorption by increased flow rate in rat ileum in vivo.

“…The derived values for the unstirred layer thickness are in the range reported for the intact rat small intestine (50)(51)(52)(53) (23). Second, the diffusion of Na, Cl, and H ions is inhibited considerably by the mucus gel layer (54,55).…”

Cholecystokinin Decreases Intestinal Hexose Absorption by a Parallel Reduction in SGLT1 Abundance in the Brush-Border Membrane

“…However, mechanism(s) involved in the CCK-induced decrease of hexose absorption have not been identified (4). Possible mechanisms involved in altering hexose transport rates include changes in the electrochemical gradient for sodium (8), the affinity of the transporter for glucose (9), and the amount of functional transporter present in the membrane (10). Recent evidence indicates that rapid up-regulation of glucose transport in jejunal enterocytes occurs by a change in the abundance of SGLT1 in the apical membrane (6,11).…”

Adaptive Changes of Sugar Absorption in Rat Small Intestine during Fasting and Refeeding

“…QPDs evoked by maltose and sucrose, which are supposed to be induced by glucose released from the hydrolysis of these disaccharides, were also changed during fasting and refeeding in the same manner as the glucose-evoked dPD. Debnam and Levin [9] reported that the decrease in dPD evoked by glucose after 3 days of fasting correlated with a decrease in enterocyte number. However, it is interesting to note the difference between dPDs evoked by disaccharides and disaccharidase activity on the first day of fasting.…”

“…However, the mechanisms regulating the adaptation of intestinal absorption are incompletely understood. Especially, the observations on the effects of fasting are contradictory, i.e., fasting has been reported to increase [7,8] or decrease [9,10] the absorption of sugars and amino acids.…”