Yeast exposure in the preparation of steamed rehmannia root improving its effects on alloxan-induced diabetic rats

The root of Rehmannia glutinosa (Gaertn.) DC. has been used in China for more than 2000 years to treat various diseases including diabetes mellitus (DM) and its complications. Steamed rehmannia root (SRR) is one of the mainly used forms. During its preparation, the material has the chance to be exposed to microorganisms, particularly yeast. The aim of this study is to verify the effect of SRR on diabetes complications and the necessity of yeast exposure. Water extract of SRR was incubated with alcohol yeast to obtain fermented SRR (FSRR). Alloxan-induced diabetic rats were administrated with medicated animal chows for 8 weeks. Urine volume, fasted blood glucose and food intake were monitored, and open field test and tail immersion test were conducted in the last week, plasma and urine samples were subjected to biochemical examinations. In DM rats, defecation in open field test was found reduced, and tail flick latency in tail immersion test increased. In the meantime, urinary excretions of Na+, K+, aldosterone, albumin and creatinine increased, and plasma concentrations of Na+, K+ and creatinine reduced and those of aldosterone, TXB2/6-Keto-PGF1α and urea nitrogen elevated. Most of these indicators were significantly improved by FSRR administration, but the effects of SRR were relatively inferior in several aspects. However, SRR and FSRR could not improve the typical symptoms of DM. Our data demonstrated that both SRR and FSRR have no obvious hypoglycemic effect, but have the potential to prevent the onset and development of diabetes complications, and this function can be improved by yeast exposure. [Display omitted]