Effect of age and diet on total and paracellular glucose absorption in nestling House sparrows

BRZEK, P.; CAVIEDES VIDAL, E; KARASOV, W. H.

PHYSIOLOGICAL AND BIOCHEMICAL ZOOLOGY

UNIV CHICAGO PRESS

Año: 2010 vol. 83 p. 501 - 511

1522-2152

Size and hydrolytic activity of the gastrointestinal tract in altricial birds undergo large and rapid changes during ontogeny. However, nothing is known about development of capacity for absorption of products of digestion, a factor that can limit total digestive performance. Using pharmacokinetic methods applied to wild-collected and laboratory-raised altricial nestlings of House sparrows (Passer domesticus), we addressed several questions of general significance about absorption in young birds. We found that both rate and efficiency of absorption of radiolabeled 3-O- methyl-D-glucose (3-OMD-glucose, absorbed by both transporter-mediated and nonmediated mechanisms) increased significantly between Days 3 and 12 posthatch. We hypothesize that these changes can explain improvement in whole-diet digestion rate and efficiency observed in young of House sparrows and many other avian species even after growth in size of their intestines has ceased. We also tested the hypothesis that a high level of nonmediated, paracellular glucose absorption, typical of adult House sparrows, would be observed already in nestlings, and that their efficiency absorbing glucose would not depend on glucose load because absorption rate is nonsaturable and matched to substrate concentration. Using L-glucose (absorbed by nonmediated mechanism(s)), we found that, as predicted, paracellular absorption accounted for the majority of total absorption in nestlings of all ages, and starch content (0 vs. 25%) in the diet of laboratory-raised nestlings had no effect on efficiency of absorption of 3-OMD-glucose. Presumably, reliance on nonmediated absorption in young sparrows can save energy for growth. Also, during the transition from almost starch-free, insect-based food during the first days posthatch to starch-rich, seed-based diet typical of adults, reliance on passive absorption is advantageous because the rate of absorption can easily match to current carbohydrate level in intestines and/or activity of hydrolytic enzymes.