Factors Limiting the Assimilation of Glucose Polymers

Kerzner, Benny

Abstract

In the young infant the mechanism for carbohydrate assimilation is not fully developed and these children are especially prone to intestinal injury. Glucose oligomers may be adequately assimilated in the healthy child despite the absence of pancreatic amylase for the first 3-6 months; the additional impact of severe prematurity or intestinal injury on oligomer uptake has not been fully characterized. Our long term objectives are to determine the efficacy and rate limiting steps of this assimilative process. We will evaluate the ability of salivary and mammary amylase to survive the acid-peptic barrier of the stomach in in vitro experiments which sequentially reproduce the physico-chemical conditions anticipated in the stomach and duodenum. After test meals, the duodenal content will be studied to determine its total endoamylase activity and, by selective inhibition of salivary amylase and electrophoretic techniques, the relative contribution of salivary amylase. Chain length of glucose oligomers is a determinant of their diffusivities and affinities for amylolytic enzymes. We will isolate from a corn starch hydrolysate a medium chain length fraction (4-10 glucose units) and a long chain fraction (more than fifty glucose units); the former is avidly digested by glucoamylase and the latter is the preferred substrate for endoamylases. To evaluate the physical limitation imposed on mucosal digestion vis-a-vis diffusivity of the oligomers and the barrier imposed by the unstirred water layer, we will extend our studies of glucose polymer assimilation by amylase-free jejunum. We will determine: 1) the diffusion coefficients of individual oligomers; 2) the effects of changes in the thickness of the unstirred water layer on the hydrolysis of glucose polymers by jejunal mucosa; 3) compare the absorption of sucrose and the oligomer fractions as well as the potential inhibition of maltatetraose absorption by medium- and long-chain oligomers. The efficiency of glucose oligomer assimilation by young infants, with limited intestinal function will be assessed by tolerance tests in which changes in blood glucose, breath hydrogen excretion, and carbohydrate losses in the stool are quantified.