Specific secretin binding sites in rat pancreas.

The dynamic nature of specific secretin binding sites in the pancreas was studied to simulate the interaction of secretin with its receptors in living organisms using isolated perfused rat pancreas. [125I]Secretin or [125I]-[Tyr1] secretin bound to certain binding sites in the perfused pancreas was displaced only by secretin in a dose-dependent manner, not by glucagon or vasoactive intestinal peptide, and the majority of the displaced radioactivity was demonstrated to be undegraded. On the basis of a secretin binding study with subcellular components, it was considered that the displacement would occur on the plasma membranes. These findings suggest that secretin which is distributed in the pancreas may rapidly and reversibly bind to specific binding sites or receptors on the plasma membranes with high affinity.