Absorption and biotransformation of four compounds in the Guizhi decoction in the gastrointestinal tracts of rats
Abstract
Objective:
To investigate the absorption and biotransformation of liquiritin, cinnamic acid, paeoniflorin, and glycyrrhizic acid—key components of the Guizhi decoction (GZD)—within the gastrointestinal tract of rats.
Methods:
A simple, reliable high-performance liquid chromatography (HPLC) method was developed and validated to simultaneously analyze these four compounds in rat gastrointestinal samples. Rats were randomly assigned to three groups: an in situ gastrointestinal loop model, an in vitro anaerobic culture model, and a blank control group. All animals were fasted for 12 hours and anesthetized with 20% urethane. An abdominal incision was made, and the stomach, duodenum, jejunum, ileum, cecum, and colon were ligated.
For the in situ loop group, 2.5 mL of GZD (1.0 g crude drug/mL, 37°C) was injected into each gastrointestinal section. The abdominal incision was covered with warm, moist cotton, and the animals were kept at 25°C. Gastrointestinal contents were collected after 1.5 hours. In the in vitro anaerobic model group, gastrointestinal contents were collected and incubated with 2.5 mL of GZD in an anaerobic environment at 25°C for 24 hours. In the control group, rats received an equivalent volume of normal saline instead of GZD. HPLC was then used to measure the concentrations of the four compounds, allowing for calculation of their absorption and biotransformation rates.
Results:
Cinnamic acid, due to its lower polarity, was more readily absorbed throughout the gastrointestinal tract compared to the more polar glycosides. The cecum exhibited the highest absorption rate. All four compounds—cinnamic acid, liquiritin, paeoniflorin, and glycyrrhizic acid—were almost completely transformed in the cecum and colon within 24 hours, while little to no transformation occurred in the stomach (except for glycyrrhizic acid). Furthermore, biotransformation was more pronounced in the distal small intestine than in the proximal sections.
Conclusion:
While some glycosides in GZD were absorbed in their original forms, the majority NSC 178886 underwent metabolic transformation by gut microbiota, primarily in the distal small intestine and beyond, before being absorbed.