Localization of insulin to gastroenteropancreatic cells in the turtle gastrointestinal tract

Insulin has been localized immunocytochemically to open-type gastroenteropancreatic endocrine cells in sections of Bouin's-fixed upper, middle, and lower intestine from Chrysemys picta, Pseudemys scripta scripta, P. scripta elegans, P. floridana, Sternotherus odoratus, and Trionyx spinifer asper. Radioimmunoassay of extracts of mucosal scrapings from Chrysemys intestine indicates differential amounts of insulin-like immunoreactivity within the intestine (higher amounts in the lower intestine) and in concentrations approximately one-tenth to one-fifth that found in extracts of Chrysemys pancreas. The presence of insulin in the gastrointestinal tract of chelonians represents a major departure from the typical vertebrate condition which is characterized by an absence of insulin from the spectrum of regulatory peptides in the gut.