Coordinated, diurnal hexose transporter expression in rat small bowel: implications for small bowel resection.
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 > or = 5), protein levels by semiquantitative Western blotting (n > or = 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.


CONCLUSIONS
Regulation of hexose absorption in rat small bowel seems to be site-specific and mediated by multiple mechanisms.
D000042:Absorption; D000818:Animals; D002940:Circadian Rhythm; D004386:Duodenum / Q000378:metabolism*; D005947:Glucose / Q000493:pharmacokinetics; D051273:Glucose Transporter Type 2 / Q000235:genetics / Q000378:metabolism; D051296:Glucose Transporter Type 5 / Q000378:metabolism; D007421:Intestine, Small / Q000601:surgery; D007583:Jejunum / Q000378:metabolism*; D008297:Male; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D051269:Sodium-Glucose Transporter 1 / Q000235:genetics / Q000378:metabolism
D051273:Glucose Transporter Type 2; D051296:Glucose Transporter Type 5; D009004:Monosaccharide Transport Proteins; D012333:RNA, Messenger; D051269:Sodium-Glucose Transporter 1; D005947:Glucose