Gastrointestinal absorption characteristics of glycyrrhizin from glycyrrhiza extract.

The differences in gastrointestinal absorption behaviors of glycyrrhizin (GZ) between pure GZ and GZ in glycyrrhiza extract (GE) (equivalent dose as GZ) were examined in rats. Similarly to the case of pure GZ, both GZ and glycyrrhetic acid (GA) were detected in the plasma after oral administration of GE. However, the plasma concentration-time curves of GZ and GA after GE oral administration were much lower than those of pure GZ, indicating the marked reduction in bioavailability of GZ and as GA after this administration. To identify the GE components affecting the absorption of GZ, GZ was removed from GE and the effect of the remaining components on the gastrointestinal absorption process of GZ was examined. The lipophilic components of GE reduced the gastric emptying rate and the absorption of GZ from the small intestine, while these effects were not observed in the hydrophilic components. In contrast, the bioavailability of GZ as GA was increased by the hydrophilic components, but not the lipophilic ones. At least some of the factors in GE altering the bioavailability of GZ were identified.