Possible Roles of the Pancreatic D-cell in the Normal and Diabetic States

The A-, D-, and B-cells—the islet cells that contain, respectively, immunoreactive glucagon, somatostatin, and insulin—are distributed within a specialized heteroceilular region of the islets of Langerhans as if to permit heterologous contacts between all three cell types. Inasmuch as each one of the three secretory products of these three cell types influences the secretion of at least one of its neighboring cells, “paracrine” influence on islet hormone secretion becomes a reasonable hypothesis. Glucagon stimulates both insulin and somatostatin release, while insulin and somatostatin both inhibit glucagon release, providing the basis for a feedback relationship through which A-cell secretion may be restrained. In addition, glucagon-mediated insulin secretion may be restrained by glucagon-stimulated somatostatin release. Such intercellular relationships could help determine the composition of the insulin and glucagon mixtures released within a given metabolic setting.