Amylin-immunoreactivity is co-stored in a serotonin cell subpopulation of the vertebrate stomach and duodenum

Amylin (or islet amyloid polypeptide) is a 37 amino acid peptide originally isolated from amyloid deposits in the pancreas of non-insulin dependent diabetic patients. It has already been immunohistochemically localised within the B and D cells of pancreatic islets and in endocrine cells of the rat and human stomach and duodenum. In this phylogenetic study, a polyclonal antiserum raised against the carboxy-terminal tridecapeptide amide of human amylin was used to demonstrate and examine the distribution of amylin-immunoreactivity in the stomach and duodenum of various vertebrate species. Except for fish, gastrointestinal tracts of all the species studied contained amylin-immunoreactive endocrine cells. They were located chiefly in the lower half portion of the distal gastric body and pyloric glands, and in the lining epithelium of the duodenal villi and crypts. Many cells were elongated, triangular or oval, and had a cytoplasmic process that extended from the cell base along the basement membrane, Others had a bipolar feature that gave them a so-called ''open'' appearance. Double and triple staining procedures on the same tissue section showed that almost all the amylin-immunoreactive cells present in the gastroduodenal region also co-stored serotonin and chromogranin A, and displayed argyrophilia in Grimelius impregnation. On the other hand, almost all the serotonin-immunoreactive cells of this region co-stored amylin, whereas those in more distal gut regions did not. This finding suggests that those amylin-containing cells correspond to a subtype of gastroduodenal serotonin cells.