Insulin cells in rat whole-pancreas isografts display heterogeneous immunoreactivities and ultrastructure

It has already been shown that insulin cells studied under experimental conditions exhibit differences in insulin immunoreactivity and insulin release. The aim of this study, therefore, was to investigate whether insulin cells themselves exhibit morphological abnormalities after transplantation. Insulin cells in rat pancreas isografts with preserved or suppressed exocrine secretion were studied immunocytochemically and ultrastructurally and compared with those of unoperated rats. In isografts with preserved exocrine secretion, cortical insulin cells connected to the exocrine parenchyma or to glucagon or somatostatin cells expressed mostly dense immunoreactivities for insulin and amylin. In addition, medullary insulin cells connected only to other insulin cells displayed faint immunoreactivities for both constituents as found in unoperated animals. After duct ligation, however, pancreatic ducts and elongated capillaries extended into the islets. Corresponding to the stages of islet fragmentation, the heterogeneity among insulin cells underwent changes and was finally abolished. Ultrastructurally, differences in the number of secretory granules paralleled the heterogeneity in insulin immunoreactivity. It is interesting to note that the heterogeneity among insulin cells is preserved after transplantation, indicating that this phenomenon might be of physiological relevance. The heterogeneity may implicate differences in insulin storage and release as found in insulin cells under normal conditions.