Mechanism and rate of glucose absorption differ between an Australian honeyeater (Meliphagidae) and a lorikeet (Loriidae)
Napier, K.R., McWhorter, T.J. and Fleming, P.A. (2008) Mechanism and rate of glucose absorption differ between an Australian honeyeater (Meliphagidae) and a lorikeet (Loriidae). Journal of Experimental Biology, 211 (22). pp. 3544-3553.
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Efficient mechanisms of glucose absorption are necessary for volant animals as a means of reducing mass during flight: they speed up gut transit time and require smaller volume and mass of gut tissue. One mechanism that may be important is absorption via paracellular (non-mediated) pathways. This may be particularly true for nectarivorous species which encounter large quantities of sugar in their natural diet. We investigated the extent of mediated and non-mediated glucose absorption in red wattlebirds Anthochaera carunculata (Meliphagidae) and rainbow lorikeets Trichoglossus haematodus (Loriidae) to test the hypothesis that paracellular uptake accounts for a significant proportion of total glucose uptake in these species. We found that routes of glucose absorption are highly dynamic in both species. In lorikeets, absorption of L-glucose (non-mediated uptake) is slower than that of D-glucose (mediated and non-mediated uptake), with as little as 10% of total glucose absorbed by the paracellular pathway initially (contrasting previous indirect estimates of ∼80%). Over time, however, more glucose may be absorbed via the paracellular route. Glucose absorption by both mediated and non-mediated mechanisms in wattlebirds occurred at a faster rate than in lorikeets, and wattlebirds also rely substantially on paracellular uptake. In wattlebirds, we recorded higher bioavailability of L-glucose (96±3%) compared with D-glucose (57±2%), suggesting problems with the in vivo use of radiolabeled D-glucose. Further trials with 3-O-methyl-D-glucose revealed high bioavailability in wattlebirds (90±5%). This non-metabolisable glucose analogue remains the probe of choice for measuring uptake rates in vivo, especially in birds in which absorption and metabolism occur extremely rapidly.
|Publication Type:||Journal Article|
|Murdoch Affiliation:||School of Veterinary and Biomedical Sciences|
|Publisher:||Company of Biologists|
|Copyright:||© The Authors|
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