The diurnal periodicity of hexose transporter mRNA and protein levels in the rat jejunum: role of vagal innervation.

ABSTRACT

BACKGROUND: Protein and messenger RNA (mRNA) levels of the hexose transporters sodium-dependent glucose transporter-1, glucose transporter 2, and glucose transporter 5 follow a (daily) diurnal rhythm in rat jejunum. Because vagal innervation mediates the diurnal activity of other proteins in the rat small bowel, we hypothesized that the diurnal variation of mRNA and protein levels of these hexose transport proteins are mediated by vagal innervation. METHODS: Forty-eight rats kept in a strictly maintained, alternating 12-hour light-dark room underwent either sham laparotomy (n = 24) or bilateral total abdominal vagotomy (n = 24). Four weeks postoperatively, jejunal mucosa was harvested from 6 rats in each group at 3 am, 9 am, 3 pm and 9 pm; mRNA levels were determined by reverse transcription real-time polymerase chain reaction and protein levels by semiquantitative Western blot analysis. Transporter mRNA and protein levels were expressed as a ratio to the corresponding mRNA and protein levels of the stably expressed housekeeping gene glyceraldehyde-6-phosphate dehydrogenase. RESULTS: mRNA and protein levels for all 3 hexose transporters showed diurnal variation in sham controls (P < or = .01 for all). After vagotomy, although mRNA levels of all 3 transporters showed diurnal variation (each P < .01), diurnal variation in all 3 hexose transporter protein levels was abolished (P > .10 for all). CONCLUSIONS: Vagal innervation appears to differentially mediate the diurnal changes in hexose transporter mRNA and protein expression in the rat jejunum by posttranscriptional, and/or posttranslational processes.