CAVIEDES-VIDAL, E.; CHEDIACK, J.G.; CRUZ-NETO, A.P.; KARASOV, W.H.*; Universidad Nacional de San Luis; Universidad Nacional de San Luis; Universidade Estadual Paulista; University of Wisconsin, Madison: Sugar absorption in bats. Are they mammals or birds?
Absorption by the paracellular pathway is a declining function of molecule size, probably due to sieving in the tight junction between cells. One emerging pattern is that in birds studied to date, paracellular absorption across the intestine exceeds that in mammalian species by a factor of at least three times, when controlling for molecular size using molecular weight (MW). The relatively high paracellular absorption in birds could be interpreted to be a compensatory mechanism for birds� smaller intestinal surface areas, the latter possibly selected for to minimize body mass and thus lower the power requirements for flight. Bats share with birds both the features of flight and small intestines that are relatively smaller than in similar-sized nonflying mammals. Therefore, we predicted that paracellular absorption in bats would decline with increasing MW, and in magnitude be more bird-like than mammal-like. Artibeus literatus were captured at the campus of the Universidade Estadual Paulista in Rio Claro (Brazil) and kept with food and water ad libitum. Using a standard pharmacokinetic technique, we gavaged or injected the relatively inert carbohydrates L-rhamnose (MW = 164 Da) and cellobiose (MW = 342 Da) and subsequently measured the appearance of probes in blood over time (HPLC with fluorescence detector) to calculate the fractional absorption (F) of the probes. As predicted, F declined with increasing MW (rhamnose, 91 +/- 1%; cellobiose, 20 +/- 7%) and was much higher than observed previously in mammals but similar to the high values in birds. Thus, the data support this first test of the hypothesis of a functional convergence in paracellular absorption for water-soluble compounds by flying vertebrates. Supported by FONCYT (01-03101), UNSL CyT 9502 to EC-V, NSF IBN-0216709 to WHK.
