INVITRO CONCENTRATIVE ACCUMULATION OF D-XYLOSE BY JEJUNUM FROM HORSESAND RABBITS

Accumulation of D-xylose by jejunal mucosa from healthy horses and rab bits was studied in vitro. When tissue sheets were incubated with 1 mM D-xylose for 60 minutes, mucosa from horses and rabbits accumulated D -xylose against a concentration gradient. There was no accumulation wh en equine specimens were incubated with 5 mM D-xylose. By comparison, equine jejunum accumulated D-glucose against a concentration gradient when incubated in 5 mM D-glucose. In equine and rabbit jejunum, 13.3 /- 7.0% and 36 +/- 11.0%, respectively, of accumulated D-xylose was ph osphorylated when sheets were incubated in 1 mM D-xylose. Short-circui t current and potential difference were lower in equine jejunum than i n rabbit jejunum, possibly because of differences in tissue thickness. None of the transmucosal electrical measurements increased after addi tion of D-xylose (1 mM and 5 mM) or D-glucose (5 mM). The active trans port system for D-xylose has a low affinity for this sugar and becomes saturated at low intraluminal concentrations. Therefore, abnormal D-x ylose absorption test results in horses are more likely caused by abno rmalities in mucosal surface area and mucosal permeability than by abn ormalities of nutrient carbohydrate absorption.