Immunocytochemical localization of prosomatostatin fragments in maturing and mature secretory granules of pancreatic and gastrointestinal D cells.

Pancreatic and gastrointestinal D cells were examined by immunocytochemistry using antisera against somatostatin-28 (SS28) and its NH2-terminal fragment SS28-(1-12), followed by the staphylococcal protein A-gold (pAg) complex. In pancreatic and gastric D cells incubated with antiserum against SS28-(1-12) the gold particles produced intense staining of the mature secretory granules but weaker staining of the immature granules associated with the Golgi area, whereas after SS28 antiserum treatment the particles accumulated selectively over the population of immature secretory granules. In intestinal D cells not only SS28-(1-12) but also SS28 antiserum produced an intense gold staining over the mature delta granules. These observations show that the relative amounts of immunoreactive sites related to SS28 and its cleavage product SS28-(1-12) in maturing and mature secretory granules are different in pancreatic, gastric, and intestinal D cells.