Tissue and plasma levels of immunoreactive gastrin and cholecystokinin in chickens with and without bombesin.

Immunoreactive gastrin and immunoreactive cholecystokinin were measured in chicken tissue extracts obtained from the gut and brain. In contrast to that found in mammals, immunoreactive gastrin found in chickens was higher in the brain than in gut tissues, and it was highest in the ileum when compared with other gut tissues. Dose-response curves of tissue extracts from the brain and ileum and of serum were parallel to the dose-response curve of synthetic human gastrin, suggesting the existence of gastrin or a peptide immunologically similar to gastrin in those chicken tissues. Immunoreactive cholecystokinin in tissues was highest in the duodenum, followed by the jejunum, ileum, and cortex; lesser amounts of cholecystokinin were found in other tissues. Influence of bombesin on the release of immunoreactive gastrin and immunoreactive cholecystokinin in the blood of chickens was also studied. Bombesin doses of 3 micrograms/kg per hour significantly increased immunoreactive gastrin in serum and immunoreactive cholecystokinin in plasma, whereas gastrin did not increase with a bombesin dose of 0.6 micrograms/kg per hour. The results confirm the existence of immunoreactive gastrin and immunoreactive cholecystokinin in the tissue of chickens and indicate that they are released into circulation in response to bombesin.