HEXOSE TRANSPORTER EXPRESSION IN RAT SMALL-INTESTINE - EFFECT OF DIETON DIURNAL-VARIATIONS

In rodents, a number of intestinal digestive and absorptive processes demonstrate a diurnal pattern of activity. To investigate if the jejun al hexose transporters are regulated in such a diurnal fashion, the le vels for the glucose and fructose transporter mRNA and proteins were d etermined at 6-h intervals over a 24-h control fed period. SGLT-1, GLU T-2, and GLUT-5 mRNA levels increased between two- and eightfold befor e the onset of peak feeding. GLUT-5 protein levels also varied in a di urnal fashion but were out of phase with the observed changes in GLUT- 5 mRNA levels. In contrast, GLUT-2 protein levels remained relatively constant during the control fed 24-h period. The effect of dietary man ipulations on the observed diurnal variation was also investigated. Af ter only 3 h of feeding a 60% fructose-enriched diet, the levels of GL UT-5 mRNA and protein were significantly elevated. GLUT-5 mRNA and pro tein levels remained elevated relative to the level of control diet-fe d animals over the ensuing 24 h and during the 7th day of fructose fee ding. Exposure to elevated levels of fructose had no significant effec t on the diurnal pattern of GLUT-2 and SGLT-1 mRNA. In contrast, GLUT- 2 protein was rapidly downregulated during the length of the fructose feeding study. In conclusion, the data demonstrate a normal daily vari ation in the level of hexose transporter expression that can be rapidl y modulated by diet.