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Absorption of sugars in the Egyptian fruit bat (Rousettus aegyptiacus): a paradox explained

Tracy, Christopher, Mcwhorter, T., Korine, C., Wojciechowski, M., Pinshow, B. and Karasov, W. (2007). Absorption of sugars in the Egyptian fruit bat (Rousettus aegyptiacus): a paradox explained. The Journal of Experimental Biology,210(10):1726-1734.

Document type: Journal Article
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IRMA ID 78672763xPUB28
Title Absorption of sugars in the Egyptian fruit bat (Rousettus aegyptiacus): a paradox explained
Author Tracy, Christopher
Mcwhorter, T.
Korine, C.
Wojciechowski, M.
Pinshow, B.
Karasov, W.
Journal Name The Journal of Experimental Biology
Publication Date 2007
Volume Number 210
Issue Number 10
ISSN 1477-9145   (check CDU catalogue open catalogue search in new window)
Scopus ID 2-s2.0-34250784062
Start Page 1726
End Page 1734
Total Pages 9
Place of Publication United Kingdom
Publisher Company of Biologists
0606 - Physiology
HERDC Category C1 - Journal Article (DEST)
Abstract Two decades ago D. J. Keegan reported results on Egyptian fruit bats (Rousettus aegyptiacus, Megachiroptera) that were strangely at odds with the prevailing understanding of how glucose is absorbed in the mammalian intestine. Keegan's in vitro tests for glucose transport against a concentration gradient and with phloridzin inhibition in fruit bat intestine were all negative, although he used several different tissue preparations and had positive control results with laboratory rats. Because glucose absorption by fruit bats is nonetheless efficient, Keegan postulated that the rapid glucose absorption from the fruit bat intestine is not through the enterocytes, but must occur via spaces between the cells. Thus, we hypothesized that absorption of water-soluble compounds that are not actively transported would be extensive in these bats, and would decline with increasing molecular mass in accord with sieve-like paracellular absorption. We did not presume from Keegan's studies that there is no Na+-coupled, mediated sugar transport in these bats, and our study was not designed to rule it out, but rather to quantify the level of possible non-mediated absorption. Using a standard pharmacokinetic technique, we fed, or injected intraperitonealy, the metabolically inert carbohydrates L-rhamnose (molecular mass=164 Da) and cellobiose (molecular mass=342 Da), which are absorbed by paracellular uptake, and 3-O-methyl-D-glucose (3OMD-glucose), a D-glucose analog that is absorbed via both mediated (active) and paracellular uptake. As predicted, the bioavailability of paracellular probes declined with increasing molecular mass (rhamnose, 62±4%; cellobiose, 22±4%) and was significantly higher in bats than has been reported for rats and other mammals. In addition, fractional absorption of 3OMD-glucose was high (91±2%). We estimated that Egyptian fruit bats rely on passive, paracellular absorption for the majority of their glucose absorption (at least 55% of 3OMD-glucose absorption), much more than in non-flying mammals.
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