Common cytochemical and ultrastructural characteristics of cells producing polypeptide hormones (the APUD series) and their relevance to thyroid and ultimobranchial C cells and calcitonin

Abstract

Five principal cytochemical characteristics, and a number of ultra structural features, are shared by cells whose common property is the synthesis and secretion of polypeptide hormones. The three cytochemical characteristics common to all eight cell types are described by the letters APUD (amine and precursor uptake and decarboxylation), and the cells are considered to belong to the APUD series. All of the cells are situated in the intestinal tractor in glands or tissues which are derivatives of the primitive digestive tube. Those with a known polypeptide hormone product include pituitary corticotrophs and melanotrophs, and the pancreatic islet α2 an β cells. Evidence is presented to show that the thyroid and ultimobranchial C cells, with their product calcitonin, fall in the same category. It is suggested that the remaining cells in the APUD series (pancreatic islet α1 cells, intestinal enterochromaffin cells, gastric and other argyrophil cells) are likely to have, as their primary function, the synthesis and secretion of polypeptides. These may be known polypeptide hormones or principles as yet undiscovered.