Expression of the five different somatostatin receptor subtypes in endocrine cells of the pancreas

Knowledge concerning tissue-specific expression of the five somatostatin receptor subtypes is of great importance in understanding their physiological function. We developed rabbit polyclonal antibodies specific for each human somatostatin receptor subtype and report our results concerning the expression in normal endocrine pancreatic cells. The antibodies were produced by immunizing rabbits with fragments specific for the five cloned somatostatin receptor subtypes. Colocalization of these somatostatin receptors with the four major islet hormones--insulin, glucagon, somatostatin, and pancreatic polypeptide--was studied in normal human endocrine pancreatic cells, using double-immunofluorescence staining. High expression of somatostatin receptor subtypes 1, 3, and 4 was found in all endocrine pancreatic cells. Somatostatin receptor subtype 2 was frequently expressed in alpha and beta cells, whereas expression was low in pancreatic polypeptide cells and intermediate in delta cells. Somatostatin receptor subtype 5 was expressed in most beta and delta cells but almost absent in alpha and pancreatic polypeptide cells. There is a variability in the normal expression of somatostatin receptor subtypes among the different human endocrine pancreatic cells. Knowledge of this expression and the physiological function mediated by these receptors will be valuable in the future when considering treatment of endocrine disorders.