Insulin recovery in pancreas and host organs of islet grafts

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.