EFFECT OF CHRONIC COLD-EXPOSURE ON NA-DEPENDENT D-GLUCOSE TRANSPORT ALONG SMALL-INTESTINE IN DUCKLINGS

In conditions of chronic cold exposure, ducklings develop a nonshiveri ng thermogenesis that requires a high energy expenditure. Therefore, e nergy supply becomes essential to cold-acclimated ducklings, which inc rease their intake of carbohydrate-rich food. The aim of this work was to investigate the effect of cold acclimation on the activity of the intestinal brush-border Na+-D-glucose cotransport, which is the first major step controlling glucose entrance into an organism. Cotransport activity was determined by measuring D-glucose uptake in brush-border membrane vesicles isolated from different parts of the small intestine of thermoneutral control (25 degrees C) or cold-acclimated (4 degrees C) ducklings (Cairina moschata). Two D-glucose transport sites were d escribed in ducklings: a high-affinity/low-capacity site and a low-aft inity/high-capacity site. The former was mainly located in the ileum a nd the latter in the duodenum. These two transport sites were altered differently by cold exposure. Major alterations occur in the ileum whe re 1) a reduction in the Michaelis-Menten constant and maximal transpo rt rate of the high-affinity site was observed, and 2) the occurrence of low-affinity site activity was noted in cold-acclimated ducklings, although it was not detected in the thermoneutral control group. Cold effect on the high-affinity site could be related to the changes in th e ileal brush-border membrane vesicle lipids, whereas cold effect on t he low-affinity site could be due, at least in part, to the higher gly cosyl content found in this segment. The small intestine appears then able to react to cold exposure by increasing both its mucosa mass in p roximal segments and D-glucose uptake capacity in ileum to respond to the higher energy demand induced by thermoregulatory requirements.