TRACY, C.R.; MCWHORTER, T.J.; KORINE, C.; PINSHOW, B.; KARASOV, W.H.*; Ben-Gurion University of the Negev, Israel; University of Wisconsin-Madison: A mystery solved: how the Egyptian fruit bat absorbs sugar

Two decades ago D.J. Keegan reported findings on Egyptian fruit bats (Rousettus aegyptiacus, Megachiroptera) that were mysteriously at odds with the dogma about how glucose is absorbed. Keegan�s in vitro tests for active transport by bat intestine were all negative, although he used several tissue preparations and had positive control results with laboratory rats. Because glucose absorption by bats is nonetheless efficient, he observed that �it seems necessary to postulate that the rapid glucose absorption from the bat intestine is not through enterocytes but must occur between these cells� (S. Afr. J. Sci. 80 (3):132). Thus, we predicted that absorption of nonactively-transported water soluble compounds would be more extensive in these bats than in rats, and would decline with increasing MW as predicted for sieve-like paracellular absorption. Bats were captured in Beer Sheva, Israel, and rats were studied in Madison, WI. Using a standard pharmacokinetic technique, we gavaged or injected the relatively inert carbohydrates L-rhamnose (MW = 164 Da) and cellobiose or lactulose (MW = 342 Da), and actively transported 3-O-methyl-D-glucose (3OMG), and subsequently measured the appearance of probes in blood to calculate fractional absorption (F). As predicted, F declined with increasing MW in both bats (rhamnose, 62 � 4%; cellobiose, 22 � 4%) and rats (rhamnose, 24 � 2%; lactulose, 10 � 2%), but was significantly higher in the bats, indicating higher paracellular absorption. Absorption of 3OMG was high in both species (respectively, 91 � 2% vs. 92 � 5%). We estimate that Egyptian fruit bats rely on passive, paracellular absorption for about 2/3 of glucose absorption, much more than in non-flying mammals but similar to birds. Supported by NSF IBN-0216709 to WHK.