Early enhanced beta cell replication in normoglycaemic Wistar rats in response to a subdiabetogenic dose of streptozotocin.

The effect of a single subdiabetogenic dose of streptozotocin (30 mg/kg body weight) on pancreatic insulin content and relative beta cell volume has been studied in normoglycaemic Wistar rats treated with streptozotocin either 2, 3 or 14 days after STZ was given. A single intravenous injection of streptozotocin caused a significant reduction of pancreatic insulin content, islet and beta cell volume, accompanied by a significantly diminished islet insulin content. The glucose- and 3-isobutyl-1-methylxanthine-stimulated insulin secretion was significantly lower in islets obtained 2 or 3 days after streptozotocin injection compared with those of vehicle-treated controls. 14 days after streptozotocin injection, beta cell volume and pancreatic insulin content partially recovered. At this time islet insulin content and secretory responsiveness were enhanced compared to the early phase following streptozotocin administration. The incorporation of [3H] thymidine into islet DNA was significantly enhanced at day 2 or 3 after streptozotocin application, whereas at day 14 the DNA synthesis corresponded to values from control rats. Despite persisting normoglycaemia, the beta cell volume of streptozotocin-treated rats was only 52% vs. control values, thus indicating the unresponsiveness of residual beta cells to compensate spontaneously for the beta cell loss.