Immunohistochemistry and ultrastructure of somatostatin cells with special reference to the gastroenteropancreatic (GEP) system

Abstract

Among the numerous endocrine cells in the gastroenteropancreatic (GEP) endocrine system, four main cell types have long been recognized: (1) the B cell, (2) the A cell, (3) the D cell, and (4) the EC cell. The existence of the D cell has been under considerable discussion although its histochemical and ultrastructural properties have been well established. Lacy and Greider 1 note that gastrin is attributed to D cells and Solcia et al. 2 state that “the function of the D cells remains obscure.” Initially the D cell was described by light microscopists, 3–6 and later it was confirmed to be ultrastructurally a specific cell type distinct from A and B cells. 7,8 An identical cell type was detected in the gut by histochemical staining properties 9 and by ultrastructural features. 10 Recently the detection of somatostatin as a new hormone of endocrine cells in the GEP system 11–16 tremendously expanded our knowledge of the D cell and enabled its analysis morphologically and functionally by means of immunohistochemical staining for somatostatin. Although many aspects of the D cell morphology have been clarified, a number of questions and controversies still arise. The aim of this review is to summarize current knowledge of the D cell with respect to the results obtained in our laboratory. We mainly directed our research efforts toward the ultrastructural analysis of the D cell in the gut and pancreas and its exact distribution in the GEP system.