Influence of viscous incubation media on the resistance to diffusion of the intestinal unstirred water layer in vitro

Dietary lactitol fermentation increases circulating peptide YY and glucagon-like peptide-1 in rats and humans

OBJECTIVE

Recently peptide YY (PYY) has attracted interest as a possible regulator of food intake. Release of PYY by nutrients in the distal small intestine is thought to contribute to the so-called ileal brake by inhibiting motility and secretion in the foregut. Our objective was to establish whether plasma concentrations of the gut peptides PYY and glucagon-like peptide-1 in rats and humans change in response to intake of a non-absorbable but fermentable carbohydrate.

METHODS

The acute response was determined in rats by killing animals 0, 5, 10, and 24 h after a single meal with or without lactitol (100 g/kg of semisynthetic diet) and measuring PYY and glucan-like peptide-1 concentrations in plasma. Food intake, body mass, and plasma peptide levels were also determined in rats fed the same diet for 10 d. Healthy human volunteers consumed lactitol or sucrose as a fruit-flavored drink. Breath hydrogen levels were measured at 45-min intervals over the next 7.5 h and plasma peptide concentrations were assessed after 0 and 5 h. Volunteers were also asked to complete a questionnaire to record satiety and well-being.

RESULTS

Ingestion of lactitol significantly increased the acute postprandial PYY response in rats, and prolonged consumption decreased weight gain in growing rats. In humans given a single dose of lactitol, the effects on PYY were much less marked but the postprandial decrease in circulating concentrations of PYY was attenuated. There was no effect on plasma glucan-like peptide-1.

CONCLUSION

Our observations are consistent with a role for fermentation products in the release of gastrointestinal peptides in the rat and, to a lesser extent, in humans.

Physicochemical properties and physiological effects of the (1----3)(1----4)-beta-D-glucan from oats

In summary, despite the many uncertainties regarding mode of action, these results have established that the soluble dietary fibre from oats, mainly (1----3)(1----4)-beta-D-glucan, is physiologically active in a fashion similar to guar gum. Extraction processes reduce the molecular size of the beta-glucan relative to the native cell wall polymer, and the product was of lower viscosity than a guar gum used for comparison, but this did not appear to affect either in vivo or in vitro activity under the conditions used. There remains a need to develop a clearer picture of the relationship, if any, of viscosity to activity, through dose response studies with products of different viscosity.

Influence of infusate viscosity on intestinal absorption in the rat. An explanation of previous discrepant results

Previous studies of the influence of increased luminal viscosity on intestinal absorption have yielded conflicting results ranging from no effect to a marked diminution. We measured the absorption of three probes (carbon monoxide, [14C]warfarin, 5.5 mM glucose) from a saline infusate or from saline containing 0.6% guar, which yielded a 20-fold increase in viscosity. Two animal models were used: (a) conscious nonlaparotomized rats with chronically implanted cannulas and (b) anesthetized laparotomized rats. In the anesthetized laparotomized rats, absorption was independent of perfusate viscosity. In the conscious nonlaparotomized rats, the absorption of each of the three probes was significantly greater than in the anesthetized laparotomized rats and increased viscosity caused a 60%-70% decrease in the clearance of the three probes. In anesthetized laparotomized rats, we have shown that fluid moves with laminar flow, and increased infusate viscosity cannot further reduce luminal stirring (or absorption). In conscious, nonlaparotomized rats, laminar flow is disrupted by normal gut motility causing better luminal stirring. Such stirring is inhibited by a viscous infusate resulting in decreased absorption. We conclude that the conflicting results seen in previous studies can be attributed to the model used. In conscious animals where luminal stirring was good, a viscous infusate caused decreased absorption.

The influence of guar gum on the movements of inulin, glucose and fluid in rat intestine during perfusion in vivo

A two-stage perfusion technique was used to study the effect of guar gum on the inulin-accessible space and the uptake of water and glucose in rat intestine. Pre-perfusion of test loops with low concentrations of guar, dispersed in saline, modified the rate of equilibration of inulin with the mucosal fluid space during a subsequent perfusion. The glucose absorption rate in such loops was reduced at a concentration of 50 mM, but not at 100 or 150 mM glucose. Fluid absorption was inhibited by pre-treatment with guar gum at all glucose concentrations tested. These results suggest that guar forms a layer closely associated with the mucosal surface which modifies the viscosity of the immediate fluid compartment, so that its resistance to diffusion is increased by means of an unstirred layer effect.