TRACY, C.R.; MCWHORTER, T.J.*; WOJCIECHOWSKI, M.S.; KORINE, C.; KARASOV, W.H.; PINSHOW, B.; Ben-Gurion University of the Negev, Israel; University of Wisconsin-Madison: Relatively low paracellular absorption in a reptile, the Egyptian mastigure, Uromastyx aegyptius

Paracellular (passive, non-mediated) absorption in the gut declines as a function of molecule size, probably due to sieving in the tight junction between cells. We predicted that reptiles will have low paracellular absorption like nonflying mammals, compared with two or three fold higher values in birds and bats. Alternatively, the relatively longer intestinal retention times of digesta in reptiles may lead to greater passive absorption, unless lower intestinal surface area and/or lower passive permeation per unit surface area provide a counter balance. Egyptian mastigure lizards Uromastyx aegyptius were captured in southern Israel, caged with IR lamps for basking and thermoregulation, and fed wetted chow. Using a standard pharmacokinetic technique, we gavaged or injected the relatively inert, passively absorbed carbohydrates L-arabinose (MW = 150 Da), L-rhamnose (MW = 164 Da) and cellobiose (MW = 342 Da), and the actively transported glucose analogue 3-O-methyl-D-glucose (3OMG) as a positive control, and subsequently measured the appearance of probes in blood over time to calculate the fractional absorption (F) of the probes. As expected, F declined with increasing MW of the inert probes (arabinose, 32 � 3%; rhamnose, 19 � 2%; cellobiose, 14 � 2%) and was much lower than for 3OMG (73 � 3%). We estimate that Egyptian mastigures absorb the majority of their dietary glucose by active transport, similar to nonflying mammals and unlike most birds and bats which appear to rely much more on passive, paracellular absorption. Low passive absorption may also reduce exposure to dietary water soluble toxins. Supported by NSF IBN-0216709 to WHK.