Different response of gastric inhibitory polypeptide to glucose and fat from duodenum and jejunum

Gastric inhibitory polypeptide (GIP), insulin, and blood glucose after ingestion of glucose or fat were examined in patients after gastrectomy with esophagojejunostomy or esophagoduodenostomy. After a glucose load patients without duodenal passage had significantly higher glucose and significantly smaller insulin levels than patients with duodenal passage. The fasting levels of serum immunoreactive GIP were moderately elevated and reached significantly higher levels after oral glucose ingestion in both gastrectomized groups as compared with normal subjects. In patients with preserved duodenal passage serum IR-GIP levels peaked earlier and were significantly higher than in patients without duodenal passage. In contrast to the finding after oral glucose ingestion, the IR-GIP response to an oral fat load was nearly twofold greater in patients without duodenal passage than in patients with duodenal continence. Thus, glucose-induced GIP release is mainly of duodenal and fat-induced GIP release mainly of jejunal origin. This suggests the existence of two types of GIP cells.