Ultrastructural localization of secretin in endocrine cells of the dog duodenum by the immunogold technique

Abstract
Secretin has been localized by the immunogold technique in endocrine cells of the dog duodenum — previously described as “K cells” — characterized by secretory granules with double structure consisting of a secretin-containing osmiophilic core surrounded by an argyrophil halo. Granules resembling those of dog secretin cells were also found in some ultrastructurally characterized S cells of the cat, pig, rat and rabbit duodenum, thus confirming in these species the identification of S cells with secretin cells. Conversely, the cells previously described as “S cells” in the dog lacked secretin immunoreactivity.