Abstract
The distribution of the postulated glucagon precursor, glicentin, as well as of the gastrointestinal hormone GIP (gastric inhibitory polypeptide), has been studied by immunocytochemistry and radioimmunoassay. Our results show that GIP antisera may contain a population of antibodies recognizing an immunoreactant common to glicentin and GIP. The occurrence of such common immunoreactants makes immunological distinction between the two hormones difficult and may explain previous results indicating that GIP is stored by glucagon cells. The present results indicate that GIP is produced by endocrine cells of the duodenum and jejunem and is absent from the pancreas, stomach, and large intestine. Glicentin-like immunoreactivity is displayed by A cells of the pancreas and by oxyntic A cells of the stomach, as well as by numerous glucagon-like immunoreactant (GLI) cells of the ileum and colon. Use of glucagon ad glicentin antisera of differing specificities indicates that the processing of this putative prohormone differs between A cells and GLI cells. Studies on the ontogeny of pancreatic A cells also reveal differences in the reactivity pattern of glicentin-like immunoreactivity between fetal and adult rats. Ultraimmunocytochemical studies show that glicentin-like immunoreactivity is mainly, stored in the cytoplasmic granules of pancreatic A cells.