DIETARY-REGULATION OF GLUCOSE-DEPENDENT INSULINOTROPIC PEPTIDE (GIP) GENE-EXPRESSION IN RAT SMALL-INTESTINE

The hormone, glucose-dependent insulinotropic peptide (GIP), is an imp ortant incretin regulator of the gastrointestinal tract. To investigat e whether diet is important for the control of GIP gene expression in the small intestine, GIP messenger RNA (mRNA) levels were measured in rats during fasting and after glucose or fat administration. Ribonucle ase protection analyses revealed that glucose and fat administration i ncreased GIP mRNA levels by 4-fold and 2.5-fold, respectively, compare d with the control, and that prolonged fasting decreased GIP mRNA leve ls to 44% of those of control animals. Glucose infusion increased plas ma GIP levels and tended to stimulate an increase in the GTP hormone c oncentration in the mucosa of the small intestine, Administration of f at also stimulated an increase of plasma GIP levels but did not modify tissue GIP concentrations. Prolonged fasting tended to decrease plasm a GIP levels, although GIP tissue concentrations did not change. These data suggest to decrease plasma GIP levels, although GIP tissue conce ntrations that dietary glucose or fat stimulates GIP synthesis and sec retion, and that food deprivation causes a decrease in GIP synthesis a nd secretion. This regulation involve changes at the pretranslational level and is reflected by modifications of GIP mRNA expression.