Abstract
Effects of dietary carbohydrate on disaccharide digestion and absorption were observed by measuring the transmural potential difference (ΔPD) evoked by Na+-dependent active transport of glucose, which is supposed to be produced by the hydrolysis of disaccharides.
ΔPD was measured using everted intestinal sacs prepared from jejunum of adult rats raised on isocaloric diets containing starch at 5 kcal %, 40 kcal % or 70 kcal %, and compared with the hydrolysis of respective disaccharides in the mucosal homogenate.
The rats raised on 70% starch diet showed an increase in maltase, sucrase, isomaltase activities and trehalulose (1-o-α-D-glucopyranosyl fructofuranose) hydrolyzing activity. On the other hand, trehalase activity was not influenced by starch intake. The ΔPDs evoked by glucose, maltose, sucrose, isomaltose, trehalose and trehalulose significantly increased in parallel with the starch content in the diets. A significant correlation between ΔPDevoked by glucose and ΔPD evoked by disaccharides, and also between ΔPDevoked by disaccharides and disaccharidase activities were observed. Michaelis constant (Km) of hydrolysis for maltose and sucrose and sugar concentration giving a half maximal ΔPD (Kt) for glucose, maltose and sucrose were not different between the 5% and 70% starch diet groups. However, the maximal velocity (Vmax) of hydrolysis and the maximal potential difference (ΔPDmax) increased significantly in rats raised on 70% starch diet. Moreover, sucrase-isomaltase content measured by an immunochemical method was also found to increase in rats raised on 70% starch diet.
These results suggest that starch-induced increase of disaccharidase activities are accompanied by a quantitative increased capacity to hydrolyze disaccharides and absorb the constituent monosaccharides.
(Received August 21, 1985)
