Pancreas and intestine from the painted turtle (Chrysemys picta) will serve as models for investigating insulin secretion in two diffuse endocrine systems. Chrysemys lacks the compact, highly ordered islet common to most other vertebrates and exhibits (as do other turtles) a substantial population of intestinal insulin cells a condition which is virtually unique among vertebrates. Constituent pancreatic endocrine cell population will be determined morphometrically to assess relationships among cell types with respect to sex, season and distribution within the pancreas. The Chrysemys pancreas also will be examined at the ultrastructural level to further characterize the endocrine cell types using conventional electron microscopy and EM immunocytochemistry. The morphological basis for peptidergic regulation of insulin secretion will be determined immunocytochemically at the light and EM level. Perifused trypsin-dispersed intestinal mucosa cells enriched for B cells will be used for characterizing intestinal cell secretory function. Attempts will be made to determine in regulation on intestinal insulin secretions in vivo and the proportional contribution made by the pancreas and intestine to circulating insulin. Results from these studies will provide important basic information on insulin secretion from the endocrine pancreas and gut of Chrysemys, two diffuse endocrine systems which are atypical among vertebrates. Moreover, these investigations may provide important insights into the evolution of the vertebrate gastro-entero pancreatic endocrine systems and into the importance of local (paracrine) regulation of endocrine function.
