Paracellular absorption in laboratory mice: Molecule size-dependent but low capacity

Area of Science:

• Physiology
• Animal Biology
• Pharmacokinetics

Background:

• Nutrient absorption in the small intestine occurs via transcellular and paracellular pathways.
• Previous studies suggested lower paracellular absorption capacity in non-flying mammals compared to flying animals, based on limited size ranges.

Purpose of the Study:

• To investigate paracellular absorption in laboratory mice, the smallest non-flying mammal studied for this process.
• To compare paracellular absorption in mice with existing data from other vertebrates.

Main Methods:

• Utilized a standard pharmacokinetic technique to measure fractional absorption (f) of inert carbohydrate probes.
• Employed L-arabinose and cellobiose (paracellular markers) and 3-O-methyl D-glucose (dual pathway marker).
• Conducted 5-10 hour urine collection trials for accurate measurement of absorption.

Main Results:

• Absorption of 3-O-methyl D-glucose was nearly complete (f=0.95±0.07), indicating significant transcellular absorption.
• Absorption of L-arabinose (f=0.21±0.02) and cellobiose (f=0.13±0.02) was significantly lower, confirming limited paracellular absorption in mice.
• The results suggest a similar molecular size cut-off for paracellular absorption in mice compared to flying animals.

Conclusions:

• Mice, as small non-flying mammals, primarily absorb glucose via mediated (transcellular) processes, not the passive paracellular route.
• The effective tight junction aperture in mice appears comparable to that in flying vertebrates.
• Smaller water-soluble compounds like phenolics and alkaloids may be absorbed more significantly by flying animals than by non-flying mammals such as mice.