The ontogeny and distribution of glucagon- and pancreatic polypeptide-immunoreactive cells in the gastrointestinal tract of the chicken.

The times of first appearance and the distribution of APP- and glucagon-immunoreactive cells have been established in the embryonic chick gut between 11 days of incubation and hatching. These immunoreactive cell types appeared for the first time at 13 days of incubation, APP-immunoreactive cells in the duodenum and upper ileum and glucagon-immunoreactive cells in the proventriculus and duodenum. At 14 days, APP-immunoreactive cells were detected in the proventriculus and lower ileum and glucagon-immunoreactive cells in the pyloric region, upper and lower ileum. Thereafter both APP- and glucagon-immunoreactive cells increased in frequency until the numbers at hatching were approximated, APP-immunoreactive cells at 19 days and glucagon immunoreactive cells at 17 1/2 days of incubation. No APP- or glucagon-immunoreactive cells were found in the gizzard, caecum or rectum at any of the selected stages examined. When these types of endocrine cells first appeared, the surface epithelium of the gastrointestinal tract was relatively undifferentiated. A few glands were present in the proventriculus only, at this stage. Thereafter immunoreactive cells of both types were found in the glandular epithelium of the proventriculus, pyloric region and small intestine soon after morphogenesis had begun.