Effect of gastrin on fasting and postprandial plasma GIP release in man

In order to evaluate the mechanism behind the augmented postprandial gastric inhibitory polypeptide (GIP) release seen in patients with achlorhydria and hypergastrinemia, 8 healthy subjects were given a liquid test meal on three different days. On 1 day the meal was preceded by ranitidine (H2 receptor antagonist) to block the gastric H+ secretion. On another day the meal was also preceded by ranitidine, but on this occasion gastrin was infused intravenously during the first hour in order to induce hypergastrinemia. On a third day the meal was given along to serve as a control. Finally, 6 healthy fasting subjects were given a 1-hour intravenous infusion of gastrin after pretreatment with ranitidine. Plasma GIP responses after the meal on the days with ranitidine alone or together with the gastrin infusion did not differ significantly from that found on the control day. When gastrin was infused in the fasting state, no effect was seen on the basal GIP levels. Thus, neither exogenous gastrin nor achlorhydria seems to affect the plasma GIP release, and it appears more likely that a rapid gastric emptying rate can account for the augmented GIP response found in achlorhydric patients.