Colocalization of numerous immunoreactivities in endocrine cells of the chicken proventriculus at hatching

The colocalization of regulatory peptide immunoreactivities in endocrine ce lls of the chicken proventriculus at hatching has been investigated using t he avidin-biotin technique in serial sections and double immunofluorescence in the same section for light microscopy, and double immunogold staining f or electron microscopy. In addition to the eight immunoreactivities previou sly described in this organ, cells immunoreactive for peptide histidine iso leucine (PHI), peptide gene product 9.5 (PGP), and the amidating enzyme, pe ptidylglycine alpha-amidating monooxygenase (PAM) were observed. All the ce lls immunoreactive to glucagon were also immunostained by the PHI antiserum . In addition, all the glucagon-like peptide 1, avian pancreatic polypeptid e, and some of the neurotensin-like cells costored also glucagon- and PHI-i mmunoreactive substances. PGP- and PAM-immunoreactivities were also found i n the glucagon-positive cells. A small proportion of the somatostatin-conta ining cells were positive for PHI but not for other regulatory peptides. Th ese results could suggest either the existence of a very complex regulatory system or that the endocrine system of the newborn chickens is not yet ful ly developed.