GLUCOSE AND AMINO-ACID-ABSORPTION IN-HOUSE SPARROW INTESTINE AND ITS DIETARY MODULATION

We acclimated house sparrows (Passer domesticus; 26 g) to high-starch (HS), high-protein (HP), and high-lipid (HL) diets and tested the pred ictions that uptake of D-glucose and amino acids will be increased wit h increased levels of dietary carbohydrate and protein, respectively. HS birds had lower mediated D-glucose uptake rate than HP birds. Total uptake of L-leucine at low concentration (0.01 mM), but not of L-prol ine at 50 mM, was increased by dietary protein. Measures of D-glucose maximal mediated uptake (1.2+/-0.2 nmol . min(-1). mg(-1)) and intesti nal mass (1 g) indicated that the intestine's mediated uptake capacity was only similar to 10% of the D-glucose absorbed at the whole animal level. This implied that nonmediated glucose absorption predominated. We applied a pharmacokinetic technique to measure in vivo absorption of L-glucose, the stereoisomer that does not interact with the Na+-glu cose cotransporter. At least 75% of L-glucose that was ingested was ap parently absorbed. This adds to the increasing evidence that substanti al passive glucose absorption occurs in birds and may explain why medi ated D-glucose uptake does not increase on high-carbohydrate diets.