A secretagogue is a substance that causes another substance to be secreted.
One example is gastrin, which stimulates the H/K ATPase in the parietal cells (increased gastric acid production by the stomach). Pentagastrin, a synthetic gastrin, histamine, and acetylcholine are also gastric secretagogues.
Insulin secretagogues, such as sulfonylureas, trigger insulin release by direct action on the KATP channel of the pancreatic beta cells. Blockage of this channel leads to depolarization and secretion of vesicles.