No abstract

The distribution of gastrin-, cholecystokinin-, glucagon-, secretin-, vasoactive intestinal polypeptide-, substance P-, bombesin-, neurotensin-, motilin-, somatostatin- and avian pancreatic polypeptide-like cells, demonstrated by indirect immunocytochemistry, was studied in samples from the following regions: proventriculus, gizzard, pylorus, duodenum, upper and lower ileum, caeca and rectum. The pylorus is particularly rich in gastrin-, neurotensin- and somatostatin-like cells. No cells immunoreactive for gastric inhibitory polypeptide or insulin were detected. In a number of instances the same cells were found to stain with antisera raised to different gut peptides. This happened with antisera detecting gastrin- and neurotensin-like cells, with secretin, vasoactive intestinal polypeptide, glucagon and substance P. The possibility that antigenic determinants to more than one peptide are contained in certain endocrine-like cells is considered.

No abstract

Little being known about factors necessary for insulin cell differentiation, we tested the chance observation that these cells were virtually absent from collagen gel cultures of embryonic avian pancreas in which the other pancreatic endocrine cells were numerous. Five-day dorsal buds stripped of their enveloping mesenchyme were embedded in gel and overlaid by a defined medium containing serum, then cultured for 7 days. Immunocytochemical evaluation showed a very low proportion of insulin cells. Substitution of the gel by a polyamino acid coating slightly increased the proportion. In an attempt to test for ability of insulin cell formation to recover, we transferred explants first cultured in collagen gel to polyamino-acid-coated dishes for a further 7 days. No improvement resulted. In controls grown for 14 days on a polyamino acid coating, insulin cells disappeared completely. We conclude that collagen gel does not support survival and differentiation of chick embryonic insulin cells and that the medium used is lacking in some essential factor(s). Determination of their identity should prove possible by exploitation of this model.

With a view to ultimately identifying factors involved in the development of pancreatic insulin cells, we have cultured dorsal pancreatic buds from 5-day chick embryos on a basement membrane matrix (Matrigel) in a serum-free medium supplemented with selected factors. The endodermal components of the buds were freed of almost all the mesenchyme so as to eradicate as much as possible of this source of some such factors. In 7-day cultures, insulin and glucagon cells were demonstrated immunocytochemically; numbers of insulin cells were expressed as a percentage of insulin plus glucagon cell counts. Our standard medium contained insulin. Addition of tri-iodothyronine to this medium did not increase the proportion of insulin cells, but in combination with raised concentrations of glucose and essential amino acids it improved somewhat the marked increase previously recorded for these nutrient conditions. Omission of insulin from the standard medium greatly reduced the proportion of these cells; substitution of insulin by insulin-like growth factor I increased the proportion considerably more than did insulin. To test for an overall effect of growth factors, explants were cultured in standard medium on Matrigel containing reduced amounts of growth factors: the proportion of insulin cells proved to be increased over that reached on normal Matrigel. The suspicion that transforming growth factor beta1, a component of Matrigel, might act to reduce the proportion of insulin cells was tested and found to be correct. It is suggested that the different factors studied here may affect either or both of proliferation and determination in the differentiation pathway of insulin vis-à-vis glucagon cells.