Historical and pharmacological studies on rehmannia root processing- Trends in usage and comparison of the immunostimulatory effects of its products with or without steam processing and pretreatment with liquor.

The dried root of Rehmannia glutinosa (RR) is a crude drug used in traditional Japanese Kampo medicine and traditional Chinese medicine (TCM). Sometimes, the crude drug is subjected to additional processing before use.To determine the effects of steam processing and pretreatment with liquor of RR through historical investigation, analytical chemistry, and pharmacological experiments.We inspected TCM literature from the Later Han Dynasty to the present day. Dried RR steamed for 3, 6, 9, or 12 h (steamed RRs, SRRs), dried RR soaked in yellow rice wine (liquor) (liquor-RR), and dried RR steamed for 6 h pretreated with liquor (liquor-SRR) were prepared. These samples were extracted using boiling water, and the inducible effects of the extracts on granulocyte colony-stimulating factor (G-CSF) secretion in cultured enterocytes and the content of their marker compounds were evaluated by using HPLC.The effect of processing using both steaming and the pretreatment using liquor described in TCM literature over different eras was to enhance the warming effect and tonifying qi (energy) of RR. We found that SRR, processed by pretreatment with liquor, became mainstream since the Qing Dynasty. In SRR, stachyose content was decreased and fructose and manninotriose contents were increased with steaming time. However, the content of these compounds was not altered by pretreatment with liquor. RR extract induced G-CSF secretion in cultured enterocytes; moreover, the SRR extract steamed for more than 6 h had significantly stronger effects than that RR. Pretreatment with liquor did not cause any significant differences in the effects of RR or SRR.The aim of processing for RR by both steaming and pretreatment with liquor in TCM literature over different eras was to enhance the tonifying effect on qi and its immunostimulatory effect. Although the effect of RR on the induction of G-CSF secretion in intestinal epithelial cells was enhanced by steaming, this enhancement was not enhanced by the pretreatment with liquor. These results provide scientific support for steaming, but could not elucidate a reason for pretreatment with liquor in TCM theory.