ONTOGENY AND REGIONAL DISTRIBUTION OF HORMONE-PRODUCING CELLS IN THE EMBRYONIC PANCREAS OF ALLIGATOR-MISSISSIPPIENSIS

The hormones of the endocrine pancreas are believed to play an importa nt role in early development. The development of the pancreas and the appearance of hormone-producing cells during embryogenesis have been e xtensively studied in mammals and birds. Relatively little work has be en done in other vertebrates, and there are no published studies regar ding the order Crocodilia. Given the pivotal phylogenetic position of crocodilians, Alligator mississippiensis provides an interesting speci es in which to study the embryonic development of the endocrine pancre as. The aims of the present study were (1) to investigate the morpholo gical development of the pancreas and (2) to determine the initial app earance and regional distribution of the pancreatic endocrine cells in the embryonic alligator. At each stage of development serial sections of pancreatic tissue were stained with hematoxylin and eosin to aid i n morphological description. Using immunocytochemistry sections were s tained to detect the presence of insulin, glucagon, somatostatin, and pancreatic polypeptide. The dorsal pancreatic bud was first observed a t stage 8, coincident with the appearance of insulin-containing and gl ucagon-containing cells. Somatostatin-containing cells were first dete cted at stage 10. At stage 13 the ventral pancreatic bud was first obs erved. At stage 14 the dorsal and ventral pancreatic buds fused and in sulin, glucagon, and somatostatin were found throughout the pancreas. Not until stage 17 was pancreatic polypeptide first detected. Unlike t he other hormones, pancreatic polypeptide was rare or absent in the do rsal region of the pancreas. In later stages of development, somatosta tin-containing cells were the most abundant and constituted 35-40% of all hormone-containing cells. The sequence of appearance of insulin an d glucagon found in the alligator is the same as that found in mammals and birds. (C) 1994 Academic Press, Inc.