The absorption enhancement of norisoboldine in the duodenum of adjuvant-induced arthritis rats involves the impairment of P-glycoprotein.

Lindera aggregata (Sims) Kosterm root has been used in traditional Chinese medicine for the treatment of rheumatism palsy, dyspepsia and frequent urination for a long time. Norisoboldine, the main active constituent of this herb drug, possesses outstanding anti-arthritis activity. However, the in vivo disposition of norisoboldine is known to a limited extent, especially under the pathological condition of rheumatoid arthritis (RA). The aim of this study is to investigate whether and how the absorption of norisoboldine is altered in adjuvant-induced arthritis (AIA) rats. Comparative studies of the intestinal absorption of norisoboldine in normal and AIA rats at different pathological stages of the arthritis were performed using in situ single-pass intestinal perfusion, and the effects of an inhibitor of efflux proteins were also investigated. Norisoboldine was shown to be a substrate of P-glycoprotein (P-gp), as P-gp inhibitor verapamil markedly increased the permeability coefficient (P