Effects of Rehmannia glutinosa oligosaccharides on activity and gene expression of hepatic glycometabolic key enzymes in type 2 diabetic rats Optimized preparation of dry powder inhalation of Rehmannia glutinosa oligosaccharides by central composite design and response surface method Effects of Rehmannia glutinosa oligosaccharides on proliferation of 3T3-L1 adipocytes and insulin resistance Optimized preparation of dry powder inhalation of Rehmannia glutinosa oligosaccharides by central composite design and response surface method Effects of Rehmannia glutinosa oligosaccharides on activity and gene expression of hepatic glycometabolic key enzymes in type 2 diabetic rats