title: Paracellular absorption in laboratory mice: Molecule size-dependent but low capacity.
abstract: Water-soluble nutrients are absorbed by the small intestine via transcellular and paracellular processes. The capacity for paracellular absorption seems lower in nonfliers than in fliers, although that conclusion rests largely on a comparison of relatively larger nonflying mammals (>155g) and relatively smaller flying birds (<155g). We report on paracellular absorption in laboratory mice, the smallest nonflying mammal species studied to date. Using a standard pharmacokinetic technique, we measured the extent of absorption (fractional absorption=f) of inert carbohydrate probes: L-arabinose (M(r)=150.13Da) and cellobiose (342.3) that are absorbed exclusively by the paracellular route, and 3-O-methyl D-glucose (3OMD-glucose) (M(r)=194) absorbed both paracellularly and transcellularly. f was measured accurately in urine collection trials of 5-10h duration. Absorption of 3OMD-glucose by mice was essentially complete (f=0.95±0.07) and much higher than that for L-arabinose (f=0.21±0.02), indicating that in mice, like other nonflying mammals, >80% of glucose is absorbed by mediated process(es) rather than the passive, paracellular route. As in all other vertebrates, absorption of cellobiose (f=0.13±0.02) was even lower than that for L-arabinose, suggesting an equivalent molecular size cut-off for flying and nonflying animals and thus a comparable effective TJ aperture. An important ecological implication is that smaller water-soluble plant secondary metabolites that have been shown to be absorbed by the paracellular path in cell culture, such as phenolics and alkaloids, might be absorbed in substantial amounts by bats and small birds relative to nonflying mammals such as mice.
authors.affiliation: Laboratorio de Biología Professor E. Caviedes Codelia, Facultad de Ciencias Humanas, Universidad Nacional de San Luis, 5700 San Luis, Argentina.
authors.forename: Verónica
authors.initials: V
authors.lastname: Fasulo
authors.forename: ZhiQiang
authors.initials: Z
authors.lastname: Zhang
authors.forename: Edwin R
authors.initials: ER
authors.lastname: Price
authors.forename: Juan G
authors.initials: JG
authors.lastname: Chediack
authors.forename: William H
authors.initials: WH
authors.lastname: Karasov
authors.forename: Enrique
authors.initials: E
authors.lastname: Caviedes-Vidal
mesh_terms: D019325:3-O-Methylglucose / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000652:urine; D000818:Animals; D001089:Arabinose / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000652:urine; D001693:Biological Transport, Active; D002250:Carbon Radioisotopes / Q000378:metabolism; D002475:Cellobiose / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000652:urine; D002851:Chromatography, High Pressure Liquid; D020895:Enterocytes / Q000378:metabolism; D005260:Female; D005947:Glucose / Q000378:metabolism*; D007408:Intestinal Absorption; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D008970:Molecular Weight; D013045:Species Specificity; D013997:Time Factors
chemical_list: D002250:Carbon Radioisotopes; D019325:3-O-Methylglucose; D002475:Cellobiose; D001089:Arabinose; D005947:Glucose