Intestinal perfusion indicates high reliance on paracellular nutrient absorption in an insectivorous bat Tadarida brasiliensis

Abstract

Flying vertebrates have been hypothesized to have a high capacity for paracellular absorption of nutrients. This could be due to high permeability of the intestines to nutrient-sized molecules. We performed intestinal luminal perfusions of an insectivorous bat, Tadarida brasiliensis. Using radio-labeled molecules, we measured the uptake of two nutrients absorbed by paracellular and transporter-mediated mechanisms (L-proline, MW 115, and D-glucose, MW180) and two carbohydrates that have no mediated transport (L-arabinose, MW 150, and lactulose, MW 342). Absorption of lactulose (0.61±0.06 nmol min-1 cm-1) was significantly lower than that of the smaller arabinose (1.09±0.04 nmol min-1 cm-1). Glucose absorption was significantly lower than that of proline at both nutrient concentrations (10 mM and 75 mM). Using the absorption of arabinose to estimate the portion of proline absorption that is paracellular, we calculated that 25.1±3.0% to 66.2±7.8% of proline absorption is not transporter mediated (varying proline from 1 mM to 75 mM). These results confirm our predictions that 1) paracellular absorption is molecule size selective, 2) absorption of proline would be greater than glucose absorption in an insectivore, and 3) paracellular absorption represents a large fraction of total nutrient absorption in bats