Glucagon releasing activity of a cyclic peptide related to somatostatin.

A possible benefit of creating smaller and more rigid active analogs of somatostatin is the discovery of compounds which selectively inhibit the secretion of insulin, glucagon or growth hormone. A series of cyclic tetrapeptide analogs related to somatostatin was synthesized, and one member of this series was found to cause an unexpected stimulation of glucagon secretion while having little if any effect on either insulin or growth hormone secretion. A sustained increase in plasma glucose levels was also observed. Two possible modes of action are proposed.