Target organs for avian pancreatic polypeptide.

The problem of the physiological function of pancreatic polypeptide (PP) has been approached by attempting to identify target organs. Avian PP (aPP) labeled with 125I at either the C-terminus (aPP-C) or the N-terminus (aPP-N) was injected into fasted chickens and allowed to circulate for 3-120 min. At the end of the equilibration period, the anesthetized bird was perfused first with saline, then with Buoin's solution. Samples of fixed tissue from various organs were collected, weighed, and counted. Control experiments consisted of coinjection of unlabeled aPP to compete for receptors. The rate of disappearance of aPP-N from plasma was greater than that of aPP-C. Binding of aPP-N by spleen, duodenum, ileum, pancreas, and bone marrow was markedly reduced by coinjection of unlabeled aPP. A similar but less marked reduction in binding was found in liver and proventriculus. aPP-C gave less conclusive results. The maximal competitive effect of unlabeled PP could be achieved in most cases with 30 microgram unlabeled aPP. It is concluded that pancreas, duodenum, ileum, spleen, and bone marrow, and probably liver and proventriculus, are target organs for aPP in the chicken and that the C-terminal region of aPP is involved in receptor binding.