Glucagon expression shift in a syngeneic single-donor intrahepatic rat islet transplantation model

In the native rat pancreas glucagon is expressed by alpha cells in the outer layer of the spheroid islet, producing a circular immunohistochemical staining pattern. We asked whether this pattern would remain unchanged after short-term and long-term intrahepatic islet transplantation. Islets of inbred Lewis rats were isolated with liberase, purified by discontinuous density gradients, handpicked, and cultured for 24 hours. After rats were rendered diabetic with streptozotocin, islets were implanted intraportally. Transplanted animals were sacrificed at 1 to 2 days (n = 5) or 100 days (n = 6). Islet clusters were detected by hematoxylen-and-eosin staining. Serial slides were stained for glucagon and insulin with the alkaline phosphatase and alkaline phosphate method at 1 to 2 days after transplantation islets with strong insulin expression were found within the portal vein branches. However, glucagon staining showed an incomplete circular staining pattern. After 100 days insulin expression remained strong, whereas only few glucagon-expressing cells were detected. Intrapancreatic islets showed inversion of the ratio of insulin- to glucagon-positive cells in favor of the glucagon-expressing cells that now composed the major part of the islet. Streptozotocin had selectively damaged beta cells in the recipient. In transplanted islets glucagon expression faded over time, possibly due to a functional involution process or to stress/inflammatory mechanisms during the isolation, transplantation, and the posttransplantation periods.