Morphological bases for intestinal paracellular absorption in bats and rodents

Area of Science:

• Comparative anatomy
• Gastrointestinal physiology
• Mammalian adaptation

Background:

• Flying mammals (bats) display distinct intestinal adaptations, including reduced surface area but enhanced paracellular glucose absorption compared to nonflying mammals.
• The precise mechanisms underlying this enhanced paracellular absorption remain unclear.
• Intestinal surface area and micro-anatomy are crucial for absorptive capacity via transcellular and paracellular pathways.

Purpose of the Study:

• To investigate the micro-anatomical basis for high paracellular nutrient absorption in bats.
• To compare intestinal villi architecture, enterocyte size, and number between microchiropterans (bats) and rodents.

Main Methods:

• Histological analysis of intestinal tissues from nine bat species and nine rodent species using hematoxylin and eosin staining.
• Measurement of nominal surface area (NSA), villous enhancement of surface area (SEF), villi length, villi density, and enterocyte dimensions.
• Comparative analysis incorporating data from published studies with similar methodologies.

Main Results:

• Bats possess shorter intestines and approximately 41% less nominal surface area (NSA) than rodents, even after correcting for body size.
• Bats exhibit a significantly greater villous enhancement of surface area (SEF) (~64%), primarily due to longer and denser villi.
• Enterocyte density per cm² NSA was ~103% higher in bats, while total enterocyte number per animal was similar; enterocyte diameter was comparable between taxa.

Conclusions:

• Increased enterocyte density per unit of nominal surface area in bats likely correlates with a higher density of tight junctions.
• This enhanced tight junction density provides a mechanistic explanation for the observed high paracellular absorption in bats.
• The study elucidates how bats compensate for reduced intestinal length with specialized villi architecture to maintain nutrient absorption.