Hydrolysis-dependent absorption of disaccharides in the rat small intestine - (Chronic experiments and mathematical modeling)

In order to throw light on the mechanisms responsible for the enzyme-depend ent absorption of disaccharides membrane hydrolysis of maltose and trehalos e and the absorption of glucose (free and that derived from disaccharides) were studied in isolated loops (20 cm) of the rat small intestine in chroni c experiments. The rates of glucose absorption were 0.26-0.81 mu mol.min(-1 ).cm(-1) when the loop was perfused with a 12.5 to 75.0 mmol/l free glucose solution, which is only insignificantly higher than the rates observed dur ing perfusion with equivalent maltose solutions. The coupling coefficient ( the ratio of glucose absorption rate to the rate of disaccharide hydrolysis ) decreased from 0.90 to 0.60 with the increasing maltose concentrations in the infusate from 6.25 to 37.5 mmol/l, but remained unchanged (approximate to 0.95) within the same range of trehalose concentrations. The permeabili ty of the pre-epithelial barrier was equivalent to that of unstirred water layer of less than 40 mu m thickness. Fluid absorption was within the range of 0.73-2.55 mu l.min(-1) cm(-1), and it showed a correlation with the rat es of glucose absorption. The result agree with a model developed on the as sumption that free glucose and that released from disaccharides share the s ame membrane transporters. It could be concluded that a close coupling of d isaccharide hydrolysis with derived glucose absorption in chronic experimen ts is achieved mainly due to a high activity of glucose transporters, which are presumably not associated with membrane disaccharidases. The transcell ular active transport is a predominant mechanism of disaccharide-derived gl ucose absorption under conditions close to physiological.