Intestinal Water Absorption Varies with Expected Dietary Water Load among Bats but Does Not Drive Paracellular Nutrient Absorption

Abstract

Rapid absorption and elimination of dietary water should be particularly important to flying species and were predicted to vary with the water content of the natural diet. Additionally, high water absorption capacity was predicted to be associated with high paracellular nutrient absorption due to solvent drag. We compared the water absorption rates of sanguivorous, nectarivorous, frugivorous, and insectivorous bats in intestinal luminal perfusions. High water absorption rates were associated with high expected dietary water load but were not highly correlated with previously measured rates of (paracellular) arabinose clearance. In conjunction with these tests, we measured water absorption and the paracellular absorption of nutrients in the intestine and stomach of vampire bats using luminal perfusions to test the hypothesis that the unique elongated vampire stomach is a critical site of water absorption. Vampire bats' gastric water absorption was high compared to mice but not compared to their intestines. We therefore conclude that (1) dietary water content has influenced the evolution of intestinal water absorption capacity in bats, (2) solvent drag is not the only driver of paracellular nutrient absorption, and (3) the vampire stomach is a capable but not critical location for water absorption.

Intestinal paracellular absorption is necessary to support the sugar oxidation cascade in nectarivorous bats

“…Our whole-animal measurements on L. yerbabuenae are consistent with those made by intestinal perfusion in situ in nectarivorous G. soricina (Price et al, 2015b), and the data on both species and methodologies underscore the importance of paracellular absorption in supporting the sugar oxidation cascade in nectarivorous bats. In the perfusion study, paracellular sugar absorption rates were high and could account for an estimated 93% (±10%, N=2; E.R.P., personal observation) of total 3OMD-glucose absorption at a luminal concentration of 10 mmol l −1 , and this percentage would be higher at higher, more transportersaturating luminal concentrations.…”

“…Moreover, the measured permeability of the in situ perfused intestine was high enough to account for the rate of glucose oxidation during hovering flight, which was about 2.2 µmol min −1 g −1 body mass (see Introduction). The passive clearance of the paracellular probe during in situ perfusion corresponded to a D-glucose clearance of 12.9 µl min −1 cm −2 (Price et al, 2015b), or 6.45 µl min −1 g −1 body mass, assuming 0.5 cm 2 g −1 body mass for a bat of its size (Price et al, 2015a). Thus, the necessary luminal glucose concentration for passive absorption rate to equal the rate at which dietary glucose was apparently absorbed and oxidized would be 0.34 µmol µl −1 (=2.2 µmol min −1 g −1 /6.45 µl min −1 g −1 ), or 340 mmol l −1 glucose.…”

Intestinal Permeability and Drug Absorption: Predictive Experimental, Computational and In Vivo Approaches

“…These paracellular pores can also have different charge-selectivity, based on the claudin proteins (a large family of proteins that modulate paracellular permeability [59,60]. More research is required on the mechanisms that underlie differences in paracellular absorption for drugs of different sizes (g/mol), both within and between species (Figure 4A,B) [58,61]. Although we have some information on the roles of individual claudins, some of which are thought to form charge- and size-selective tight-junction pores for smaller molecules, relatively little is known about their interactions [62].…”

An overview of bats microbiota and its implication in transmissible diseases

“…The stomach forms a U shape blind-ending tube extremely long and thin ( Rouk and Glass, 1970 ). Furthermore, the main functions of this organ are storage of large volume of blood and high water absorption ( Mitchell and Tigner, 1970 ; Price et al, 2015 ).…”