AJP - Regulatory, Integrative and Comparative Physiology, Vol 271, Issue 3 561-R568, Copyright © 1996 by American Physiological Society
Glucose and amino acid absorption in house sparrow intestine and its dietary modulation
E. Caviedes-Vidal and W. H. Karasov
Departamento de Bioquimica y Ciencias Biologicas, Universidad Nacional de San Luis, Argentina.
We acclimated house sparrows (Passer domesticus; 26 g) to high-starch (HS),
high-protein (HP), and high-lipid (HL) diets and tested the predictions
that uptake of D-glucose and amino acids will be increased with 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-proline at 50mM, was
increased by dietary protein. Measures of D-glucose maximal mediated uptake
(1.2 +/- 0.2 nmol.min-1.mg-1) and intestinal mass (1 g) indicated that the
intestine's mediated uptake capacity was only approximately 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(+)-glucose cotransporter. At least 75% of L-glucose
that was ingested was apparently absorbed. This adds to the increasing
evidence that substantial passive glucose absorption occurs in birds and
may explain why mediated D-glucose uptake does not increase on
high-carbohydrate diets.
