Induction of hepatic bilirubin and drug metabolizing enzymes by individual herbs present in the traditional Chinese medicine, yin zhi huang.

Yin Zhi Huang (YZH) is a decoction of four plants which is widely used in Asia to treat neonatal jaundice. This study compares the ability of phenobarbital and the individual herbs comprising YZH, Artemisia, Gardenia, Rheum, and Scutellaria baicalensis, to induce hepatic drug and bilirubin metabolizing enzymes in rats. Herbal decoctions (30 ml/kg/day) or phenobarbital (60 mg/kg/day) were administered for 5 days. Only phenobarbital increased cytochrome P-450 levels whereas Gardenia slightly decreased levels. Artemisia, Rheum and phenobarbital increased bilirubin glucuronyl transferase activity. Glucuronidation of alpha-naphthol was increased by Gardenia and phenobarbital, whereas Artemisia and Rheum were ineffective inducers. Phenobarbital was the most effective inducer of glutathione-S-transferase (GSHT) activity. Phenobarbital and Gardenia both induced delta 5-3-ketosteroid isomerase activity, a marker for the Ya subunit of GSHT responsible for intracellular bilirubin transport in liver. The selective patterns of enzyme induction suggest potential value for using specific plant decoctions to modify drug and bilirubin metabolic pathways.