Effect of secretin on release of heterogeneous forms of gastrin

The effect of an intravenous injection of secretin on plasma gastrin concentration is shown to be dependent upon the relative concentration of the major forms of immunoreactive gastrin present in the plasma at the time of injection. Secretin suppressed gastrin secretion in the fasting state in patients in whose plasma heptadecapeptide and big gastrins predominated and did not suppress when big big gastrin comprised more than 90% of plasma gastrin immunoreactivity. The post-secretin decrease in plasma gastrin was due entirely to the disappearance of the smaller, more rapidly degraded forms. Food-stimulated gastrin response was suppressed by secretin for the initial 40 minutes after a test meal but was greater than usual from 40 to 120 minutes.