Inhibition of human gastric secretion by intragastrically administered calcitonin

The effects of intragastrically administered synthetic human calcitonin (H-CT) and salmon calcitonin (S-CT) on human gastric secretion have been compared with the effects of both CTs after intravenous infusion. Basal as well as pentagastrin-stimulated acid and pepsin output were lowered by about 50% in response to a single intragastric instillation of H-CT while an intravenous infusion of H-CT produced an inhibition of more than 70%. After intragastric instillation, dose-response curves of H-CT and S-CT were in a similar range when the dose was referred to the molarity of CT; however, related to the biological activity of CT (MRC units), S-CT was about 10--15 times less effective than H-CT. Conversely, after intravenous infusion, equal doses in reference to MRC units evoked similar responses while in reference to molarity S-CT was 20--30 times more effective than H-CT. Radioimmunological determinations of H-CT showed after intragastric instillation a stepwise decrease in concentration of H-CT in the gastric juice and no appearance of H-CT in the blood. In contrast, after intravenous administration of H-CT, no detectable H-CT activity was secreted into the juice in the presence of a peak increase in serum-immunoreactive H-CT. From the differences in the effects of CT observed after intragastric and intravenous administration, respectively, it is suggested that intragastrically administered CT might inhibit gastric secretion via local mechanisms on the gastric mucosa.