Endogenous and exogenous heptadecapeptide gastrin transport across the pig liver

In vivo studies in the pig showed no net loss or gain of endogenous porcine gastrin during transport across the liver in fasting animals. Infusion of synthetic human heptadecapeptide gastrin (G-17) in doses of 0,25, 0,5 and 1,0 microgram/kg/min raised circulating gastrin levels to those found in the postprandial state. At no time was there a loss or gain of immunologically determined gastrin across the liver. Changes in the molecular size of gastrin, however, suggested that qualitative but not quantitative effects followed the administration of G-17 in vivo. The disappearance of gastrin from the circulation was biphasic, with an initial half-life of 3 minutes and a slower phase suggesting recirculation or multicompartment equilibration. The distribution at equilibrium was +/- 20% of body weight calculated from arterial levels, but 30-40% if portal or hepatic venous values were used. The mean blood production rate was +/- 125 microgram/day but the portal contribution was only 30 microgram/day, suggesting an important alternative source of gastrin.