Absence of hepatic extraction of gastric inhibitory polypeptide in conscious dogs

Fractional hepatic extraction of gastric inhibitory polypeptide was examined in conscious unrestrained dogs with catheters in the portal vein, hepatic vein, and the carotid artery and Doppler flow probes on the portal vein and hepatic artery. Following a control period, endogenous gastric inhibitory polypeptide was stimulated by oral administration of glucose with and without prior infusion of atropine. In other experiments, gastric inhibitory polypeptide (20 ng/kg/min) was infused into the portal system in association with peripheral infusion of glucose. In none of these experiments was it possible to demonstrate any significant fractional hepatic extraction of gastric inhibitory polypeptide.