Paracellular intestinal transport of six-carbon sugars is negligible in the rat.
OBJECTIVE
Active D-glucose absorption has been theorized to increase convective flow and enhance tight junction permeability such that paracellular transport becomes the major mechanism of D-glucose absorption. This concept was tested in rats by measuring the absorption of four gavaged, nonmetabolizable six-carbon sugars (L-glucose, L-galactose, L-mannose, and D-mannitol) thought to be absorbed solely by the paracellular route.


METHODS
Uptake of gavaged probes was measured by recovery in 24-hour urine specimen collections.


RESULTS
L-glucose (71.2% +/- 2.4%) absorption exceeded that of the other probes (1.4%-9%). Coadministration of 3.0 mol/L D-glucose, 0.22 mol/L D-glucose, or chow significantly reduced the absorption of L-glucose to 38.1% +/- 7.2%, 61% +/- 3.3%, and 53.6% +/- 3.5%, respectively, but did not influence the absorption of the other six-carbon probes.


CONCLUSIONS
(1) L-glucose seems to have a weak affinity for a D-glucose carrier and is not a marker of paracellular transport, and (2) paracellular transport accounts for a minimal fraction of D-glucose uptake; this fraction is not enhanced by ingestion of D-glucose or chow.
Schwartz
R M
RM
VA Medical Center, Research Service, Minneapolis, Minnesota, USA.
Furne
J K
JK
Levitt
M D
MD
D000818:Animals; D001692:Biological Transport; D003106:Colon / Q000378:metabolism; D005690:Galactose / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D006601:Hexoses / Q000378:metabolism*; D007408:Intestinal Absorption / Q000502:physiology*; D008297:Male; D008353:Mannitol / Q000378:metabolism; D008358:Mannose / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
D006601:Hexoses; D008353:Mannitol; D005947:Glucose; D008358:Mannose; D005690:Galactose