Background
Hexose transporter mRNA and protein levels follow a diurnal rhythm in rat jejunum.
Their coordinated expression and resultant function throughout the small bowel is
not well understood. We hypothesized that hexose transporter levels and glucose absorption
follow a coordinated, site-specific diurnal rhythm in rat duodenum and jejunum, but
not in ileum.
Methods
Sprague-Dawley rats were housed in a strictly maintained, 12-h, light/dark room [light
6 am to 6 pm] with free access to water and chow. Mucosa was harvested from duodenum, jejunum,
and ileum at 3 am, 9 am, 3 pm, and 9 pm, and full thickness 1-cm segments were harvested at 9 am, and 9 pm (n = 6 for each segment at each time point). mRNA levels were determined by reverse-transcription,
real-time polymerase chain reaction (n ≥ 5), protein levels by semiquantitative Western
blotting (n ≥ 5), and transporter-mediated glucose uptake by everted sleeve technique
(n = 6).
Results
mRNA levels of SGLT1 and GLUT5 followed a temporally coordinated, diurnal rhythm in
all 3 segments (P < .01), while mRNA for GLUT2 and protein levels for SGLT1 and GLUT2 varied diurnally
only in duodenum and jejunum (P > .05) but not in ileum (P > .10). SGLT1 and GLUT5 mRNA induction decreased aborally. Baseline SGLT1 and GLUT5
mRNA levels and SLGT1 and GLUT2 protein levels did not vary aborally (P > .05 for all). GLUT2 mRNA baseline levels were decreased in ileum (P < .01). Glucose uptake varied diurnally in duodenum and jejunum with no difference
in ileum. Transporter-mediated glucose uptake was greater in duodenum and jejunum
compared with ileum.
Conclusion
Regulation of hexose absorption in rat small bowel seems to be site-specific and mediated
by multiple mechanisms.
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Article info
Publication history
Published online: November 30, 2007
Accepted:
June 22,
2007
Footnotes
Supported by a grant from the National Institutes of Health (NIH R01 DK39337-MGS) and the Department of Surgery, Mayo Clinic College of Medicine, Rochester, Minn.
Identification
Copyright
© 2008 Mosby, Inc. Published by Elsevier Inc. All rights reserved.
