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UBC Theses and Dissertations

Studies on the physiological release and insulinotropic action of gastric inhibitory polypeptide Schubert, Harold Edward


The effect of highly purified gastric inhibitory polypeptide (GIP) on immunoreactive insulin (IRI) secretion in the conscious fasted dog was investigated. Significant increased in IRI release were observed with intravenous administration of three different doses of GIP. These were accompanied by depression in fasting serum glucose levels. Preliminary studies were undertaken to determine whether this insulinotropic action of GIP could be attributed to a particular segment of the GIP molecule. GIP fragments produced by cleavage with cyanogen bromide (CNBr) and trypsin (TPCK) showed no significant stimulation of IRI release. The possibility that GIP might itself enhance glucose uptake or potentiate insulin-induced glucose uptake was studied using the rat hemidiaphragm preparation. No such effect was observed. The release of IR-GIP by oral glucose and fat was investigated and this release Was shown to occur in a dose-related manner. Fat was found to be the most potent secretagoge for IR-GIP reported to date but no significant change in serum IRI levels was observed following oral fat. In light of this and other recent work, the possible involvement of GIP in carbohydrate metabolism is discussed.

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