Chicken gastrin: a member of the gastrin/CCK family with novel structure-activity relationships.

The biological activity of natural chicken gastrins isolated from the "antrum"-like region of the chicken gut have been studied on gastric secretion in chickens, turkeys, and rats, pancreatic secretion in turkeys and rats, and gallbladder contraction in chickens and guinea pigs. Natural chicken gastrin was shown to be approximately 85% sulfated on the tyrosine that occurs at position 7 from the COOH-terminus. In both avian and mammalian systems, chicken gastrins were found to be potent stimulants of acid secretion but were virtually inactive as stimulants of pancreatic secretion and gallbladder contraction. Peptides with the COOH-terminal tetrapeptide amide of CCK and a sulfated tyrosine at position 7 from the COOH-terminus are usually potent stimulants of pancreas and gallbladder. However, although chicken gastrin has a CCK-like structure, it has a gastrin-like spectrum of biological actions. A proline immediately adjacent to the sulfated tyrosine may produce a steric effect that lowers the activity of chicken gastrin on pancreas and gallbladder. Evidently, then, the factors that determine specificity of action of CCK and gastrin are different in birds and mammals.