CONICET | Buscador de Institutos y Recursos Humanos

Flying vertebrates have been hypothesized to rely heavily on paracellular absorption of 30 nutrients to compensate for having smaller intestines than non-flyers. We tested this hypothesis 31 in an insectivorous bat (Myotis lucifugus) and two insect-eating rodents (Onychomys leucogaster 32 and Peromyscus leucopus). In intact animals, the fractional absorption of orally dosed L- 33 arabinose (Mr 150) was 82% in the bat, which was more than twice that of the rodents. 34 Absorption of creatinine (Mr 113) was greater than 50% for all species and did not differ 35 between the bat and the rodents. We also conducted intestinal luminal perfusions on 36 anesthetized animals. Clearance of L-arabinose per nominal surface area in the bat was nearly 37 double that of the rodents, while clearance of creatinine was not different among species. Using 38 an everted sleeve preparation, we demonstrated that high concentrations of L-arabinose and 39 creatinine did not inhibit their own uptake, validating their use as paracellular probes. 40 Histological measurements indicated that M. lucifugus has more cells, and presumably more tight 41 junctions, per nominal surface area than P. leucopus. This seems unlikely to explain entirely the 42 higher clearance of L-arabinose in the bat during perfusions, because L-arabinose clearance 43 normalized to the number of enterocytes was still double that of P. leucopus. As an alternative, 44 we investigated tight junction gene expression. The bat had higher expression of claudin-1 and - 45 15, and lower expression of claudin-2 relative to P. leucopus. Expression of claudin-7 and 46 occludin did not differ among species. Taken together, our results support the hypothesis that 47 bats have evolved higher paracellular nutrient absorption than non-flying animals, and that this 48 phenomenon might be driven by both histological characteristics and differences in tight- 49 junction gene expression.