Effects of soybean diet on the beta cells in the streptozotocin treated rats for induction of diabetes.

Certain dietary components have been reported to potentially suppress the initiation of experimental insulin-dependent diabetes mellitus (IDDM) in animal models. In the present study, we showed that dietary soybean prevents induction of experimental hyperglycemia by retaining beta cell activity. In rats fed raw soybean, expression of insulin mRNA in pancreatic beta cells was significantly increased compared to those fed with normal diet. In those rats and upon injection of streptozotocin, only few beta cells underwent cell death, most of them demonstrating active viability with enhanced mRNA expression and insulin content. This is consistent with the fact that blood glucose level was normalized (72.51 +/- 1.54 mg/dl) after a transitory hyperglycemic state (> 300 mg/dl). It implies the dietary soybean can prevent beta cell injury by streptozotocin. Moreover, a prolonged hyperglycemia was not observed in rats fed raw soybean even when this was substituted by the normal diet after streptozotocin injection. In contrast, in streptozotocin-treated rats fed normal diet, most beta cells were destroyed and severe hyperglycemia was observed. Although the protective effect was not recorded in the rats fed with heated soybean, some beta cells were found to retain their cell organelles for insulin secretion indicating that some heat-stable components of soybean might prevent the cytotoxic insult. Therefore, we suggest that dietary soybean protected the streptozotocin-induced beta cell damage and restrained the development of hyperglycemia in rats.