The method of insulin determination is a useful tool for detecting surviving beta cells in the pancreas of diabetic animals and in organs used as sites of islet graft. Therefore, we have studied the insulin recovery in tissue homogenates. The data show that a high recovery rate of insulin (more than 95%) was reached, when the phosphoric acid-alcoholic tissue extract was stored at -20 degrees C and diluted with RIA buffer immediately before radioimmunoassay. When acid-ethanol supernatants were neutralized the recovery rate was diminished to 73.4 +/- 4.0% in pancreas and to 61.0 +/- 6.2% in liver homogenates, respectively. Glucagon was degraded when diluted extracts were stored at -20 degrees C for different periods of time. The diabetogenic action of streptozotocin (STZ) could be demonstrated for doses ranging between 30 and 55 mg/kg body weight. STZ caused a dose-dependent decrease of pancreatic insulin whereas the glucagon content was significantly enhanced in diabetic animals. The glucagon content was not normalized when normoglycemia was achieved by syngeneic islet transplantation. Insulin extracted from spleen used as a site for transplantation of 900 neonatal rat islets showed a high biological variation ranging from 0.7 to 6.4 nmol insulin per spleen, 10-100% of the content of the equivalent number of freshly isolated islets these animals received.
The ability of transplanted islets to release insulin after stimulation with glucose was analysed. Three months after islet transplantation into the liver of diabetic rats the liver was perfused in vitro with different glucose-containing perfusion fluids. Transplanted islets preserve their functional integrity for at least three months and contribute substantially to the observed amelioration of the diabetic state. They are able to release insulin after stimulation with 16 mM glucose with a typical biphasic secretion profile. Insulin containing islets were identified by light microscopy in the tissue of the liver.
It was the aim of this study to elucidate whether intraportally transplanted pancreatic islets were reinnervated after transplantation and whether the secretion of insulin from pancreatic islets might be modulated by the vegetative innervation of recipient livers. Two weeks after intraportal transplantation of 2000 neonatal pancreatic islets recipient rats completely recovered from streptozotocin-induced diabetes. Predominantly catecholaminergic, but also cholinergic nerve fibers were detected in islet cell complexes between beta-cells. Corresponding electron micrographs showed beta-cells in close contact with axons of nonmyelinated nerve fibers. Perfusion studies with livers of recipient rats revealed that the inhibition by hepatic sympathetic nerves of insulin secretion was mediated via alpha 2-receptors as in normal pancreatic islets.
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