Role of GIP and insulin in glucose-induced changes in intestinal motility patterns

This study was designed to correlate the intestinal motility patterns with duodenal glucose loads and the increments in plasma gastric inhibitory peptide (GIP) and insulin levels after these loads or after the administration of exogenous hormones in conscious dogs. Isotonic glucose instilled intraduodenally at lower loads (5.2-42.4 mmol/h) only caused a moderate increase in spike activity, but at higher loads (84.8 mmol/h) it disrupted migrating myoelectric complexes (MMC), being accompanied by marked increases in plasma GIP and insulin levels. Duodenal loads of isotonic mannitol resulted in similar motility changes but without alteration in plasma GIP or insulin. Hypertonic glucose (20%) in the duodenum also caused an increase in spike activity, and at higher loads (72 mmol/h or higher) it disrupted MMCs and resulted in significant increments in plasma GIP and insulin levels. Physiological doses of exogenous GIP (25-400 pmol X kg-1 X h-1) or insulin (12-24 mU X kg-1 X h-1) did not affect the motility pattern, but at higher doses, raising plasma hormone over the levels occurring after a mixed meal, GIP (400 pmol X kg-1 X h-1) increased significantly the MMC interval, whereas insulin (48-96 pmol X kg-1 X h-1) induced a fed-like motility pattern. Intravenous 20% glucose (72 mmol/h) caused a marked rise in plasma insulin (but not GIP) levels but failed to affect the intestinal motility as did 20% mannitol infused intravenously in the same dose.(ABSTRACT TRUNCATED AT 250 WORDS)