Spontaneous diabetes mellitus syndrome in the rat. III. Pancreatic alterations in aglycosuric and untreated diabetic BB Wistar-derived rats.

The pancreatic alterations in aglycosuric and untreated diabetic BB Wistar-derived rats are described. A common finding, often seen in young aglycosuric rats, is that of discrete foci of periductular and/or acinar aggregates of lymphocytes and macrophages. Sites of periductular mononuclear cell infiltrates usually lack endocrine cells. In contrast, foci of acinar infiltrates, although distinct from the predominant endocrine cell mass in the islets of Langerhans, often contain small numbers of alpha and/or beta cells. It is suggested that these clusters of endocrine cells may in some way be antigenically different from those resident in the principal islets and thus serve as an additional target for the immune system in rats bearing the BB genome. The development of overt diabetes requires a massive destruction of beta cells within the islets of Langerhans. Two forms of diabetes mellitus emerge in untreated animals. The more common, designated unstable diabetes, is severe and lethal unless treated with insulin. Less commonly, a stable type of diabetes mellitus ensues for which insulin therapy is not mandatory. In each, the concentration of pancreatic immunoreactive insulin is profoundly decreased, although relatively greater amounts are present in the stable form. Unstable diabetic rats demonstrate a reduction in the concentration of pancreatic immunoreactive glucagon and somatostatin, suggesting that alpha and delta cells also sustain injury in this model of insulin-dependent diabetes mellitus.