Immunohistochemical localization of glucagon and pancreatic polypeptide on rat endocrine pancreas: coexistence in rat islet cells

We used immunofluorescence double staining method to investigate the cellular localization of glucagon and pancreatic polypeptide (PP) in rat pancreatic islets. The results showed that both A-cells (glucagon-secreting cells) and PP-cells (PP-secreting cells) were located in the periphery of the islets. However, A-cells and PP-cells had a different regional distribution. Most of A-cells were located in the splenic lobe but a few of them were in the duodenal lobe of the pancreas. In contrast, the majority of PP-cells were found in the duodenal lobe and a few of them were in the splenic lobe of the pancreas. Furthermore, we found that 67.74% A-cells had PP immunoreactivity, 70.92% PP-cells contained glucagon immunoreactivity with immunofluorescence double staining. Our data support the concept of a common precursor stem cell for pancreatic hormone-producing cells.Key words: glucagon, pancreatic polypeptide, rat, pancreas, Immunofluorescence double staining histochemistry.The pancreatic islet is comprised of numerous cell types that synthesize and secrete distinct peptide hormones. Four major cell types are recognized in pancreatic islets of many mammalian species including rat, A-cells which contain glucagon, B-cells which contain insulin, D-cells which contain somatostatin, and PP-cells which contain the pancreatic polypeptide (PP) (Erlandsen, 1980; Reddy et al., 1988).Previous studies have revealed coexistence of glucagon- and PP-like immunoreactivity in endocrine pancreas cells of frog, rat, baboon, murine, monkey, and fish (Kaung and Elde, 1980; Kaung, 1985a, 1985b; Wolfe-Coote et al., 1988; Herrera et al., 1991; Lozano et al., 1991; Park and Bendayan, 1992; Louw et al., 1997). However, those experiments were performed by staining adjacent ultrathin sections with anti-glucagon serum and anti-PP serum respectively by peroxidase antiperoxidase (PAP) or immuno-gold labeling or avidin-biotin-peroxidase method, and the situation of two kinds of positive cells were compared.It is still not clear whether one cell type contains two or more peptides. Therefore, we used immunofluorescence double staining to identify the peptides secreted by single specific cells.This is the first time that coexistence of glucagon and PP in rat islet cells has been detected by an immunofluorescence double staining method.