Immunoelectron microscopic demonstration of pancreatic polypeptide in midgut epithelium of hematophagous dipterans.

Midguts of mosquitoes, Aedes aegypti and Anopheles stephensi, and of the tsetse fly, Glossina morsitans morsitans, as well as guinea pig pancreas, were prepared for electron microscopy by using low-temperature embedding in Lowicryl K4M. Rabbit antiserum to bovine pancreatic polypeptide (PP) crossreacted with secretory granules of pancreatic PP-producing cells and of the clear cells in mosquito gut. Rabbit antiserum to human somatostatin crossreacted with the control tissue, guinea pig pancreas D-cells, but not with the mosquito clear cells. None of the antisera used showed a distinct reaction with the endocrine-like cells of tsetse fly midgut. Positive reactions were revealed by gold as electron-dense marker. The gold particles were coated with protein A-gold or goat antibodies to rabbit immunoglobulin.