Polyphenolics in the mammalian gut: Effects on glucose absorption and the efficacy of a salivary defense mechanism.

摘要

We studied the effects of polyphenolics on digestive processes in Sprague Dawley rats. We found that a variety of purified flavonoids and cranberry juice, in which we measured flavonoids, inhibited intestinal glucose absorption. Absorption of the transported but not metabolized analogue of D-glucose, 3-0-methyl D-glucose, was analyzed in vivo using a pharmacokinetic method. The percent inhibition of 3-0-methyl D-glucose absorption caused by the flavonoids, fed at a 10mm concentration, was from most to least potent: phloridzin (66%) > epigallocatechin gallate (20%) > genistein (18%) > naringenin (14%) > naringenin-7-glucoside (13%) > phloretin (11%), cranberry juice (11%) > isoquercetrin (10%) > quercetin (4%). By inhibiting glucose absorption flavonoids may alter glycemic index and digestive efficiency.; We also investigated the role of salivary proline rich proteins (PRP) in ameliorating the antinutritional effects of the hydrolysable tannin, pentagaloylglucose (PGG). Tannins are thought to be synthesized by plants as feeding deterrents. Some mammals however, have developed a physiological adaptation to tannin consumption: the secretion of PRPs in their saliva. PRP secretion is an inducible response in laboratory rats so we compared the excretion of 14C labeled PGG and apparent diet digestibility between PGG naive rats that were not secreting PRPs and PGG habituated rats that were secreting PRPs. The habituated rats excreted three times more 14C in their feces than did the naive rats. The presence of PGG in the diet of the naive rats had no significant effect on apparent dry matter or nitrogen digestibility, but the presence of PGG as well as PRPs in the habituated rats decreased apparent dry matter and nitrogen digestibility. Thus PGG did not directly retard digestion of the diet, but the rats' habituation to PGG increased endogenous fecal loss of energy and nitrogen and thus depressed apparent diet digestibility. Overall, polyphenolics have substantial effects on digestive processes that vary in mode and magnitude depending on the compound fed.