Insulin secretion in the perinatal period of the rat in vivo and in vitro effects of glucose and gibenclamide (HB 419)

Co-expression and regulation of connexins 36 and 43 in cultured neonatal rat pancreatic islets

Fetal and neonatal pancreatic islets present a lower insulin secretory response as compared with adult islets. Prolonged culturing leads to an improvement of the glucose-induced insulin secretion response in neonatal pancreatic islets that may involve regulation of gap junction mediated cell communication. In this study, we investigated the effect of culturing neonatal islet cells for varying periods of time and with different glucose medium concentrations on the cellular expression of the endocrine pancreatic gap junction associated connexin (Cx) 36 and Cx43. We report here that the 7-d culture induced upregulation of the expression of these junctional proteins in neonatal islets in a time-dependent manner. A correlation was observed between the increased mRNA and protein expression of Cx36 and Cx43 and the increased insulin secretion following islet culturing. In addition, increasing glucose concentration within the culture medium induced a concentration-dependent enhancement of Cx36 islet expression, but not of Cx43 expression in cultured neonatal islets. In conclusion, we suggest that the regulation of gap junctional proteins by culture medium containing factors and glucose may be an important event for the maturation process of beta cells observed at in vitro conditions.

Skeletal growth of fetuses from streptozotocin diabetic rat mothers: in vivo and in vitro studies

For largely unknown reasons severe or moderate diabetes of pregnant rats results in pronounced fetal growth retardation. Therefore, some skeletal growth parameters of fetal rats from streptozotocin diabetic mothers were studied in vivo and in vitro. Two days post conception rats were intravenously injected with 65 mg/kg body weight streptozotocin. On day 20 post conception 8 normal and 8 diabetic rat mothers received 5 mu Ci 3-H thymidine intraperitoneally. One day later the experiments were terminated. Fetal body weight and body length were significantly (p less than 0.05-0.001) reduced in the hyperglycaemic rats compared to normal rats, as was the thymidine incorporation into rib cartilage (p less than 0.02). In the cell culture colony formation from isolated chondrocytes of normal and hyperglycaemic fetuses was determined. Proinsulin, insulin (62.5-250 ng/ml), insulin-like growth factor I and II (6.25-25 ng/ml) significantly (p less than 0.05-0.001) augmented colony formation in a dose-dependent manner, with the somatomedins being 8 times more effective than proinsulin or insulin. Isolated chondrocytes from hyperglycaemic compared to normal fetuses formed significantly (p less than 0.05-0.001) fewer colonies in the basal state and in response to all 4 hormones. The results confirm the growth retardation of fetuses from diabetic rat mothers. A reduced responsiveness of chondrocytes from hyperglycaemic fetuses to various growth factors could be demonstrated as compared to cells from normal fetuses.