Influence of combination of extractum Angelicae Dahuricae Siccum and total alkaloids of Rhizoma Corydalis on pharmacokinetics of tetrahydropalmatine in rats

This paper is aimed to develop a rapid and sensitive HPLC-fluorescence detection (FLD) method for the determination of tetrahydropalmatine (TET) in rats’ plasma.  The influence of combinations of Extractum Angelicae Dahuricae Siccum (coumarin and volatile oil) and total alkaloids (TA) from Rhizoma Corydalis (TA) on pharmacokinetics of TET in rats was studied.  Plasma samples were treated with hexane-isopropanol (95∶5) to precipitate the protein, and were determined by HPLC-fluorescence detection.  The calibration curve was linear in the range of 2.096−167.68 μg·L⁻¹.  The limit of quantification was 2.096 μg·L⁻¹.  The method recovery of TET was 94.0%−100.0%.  The extract recovery was 72.0%−81.5%.  RSDs of intra- and inter-day precisions were all less than 7.0%.  Pharmacokinetics of TET in rats was fitted to two compartments open model after oral administration of TA, TA-volatile oil (VO), TA-coumarin (Cou) and TA-VO-Cou.  Compared with TA, AUC_0−t, AUC_0−∞, MRT_0−t and MRT_0−∞ of TET had significant deviation when combined with VO and/or Cou.  The   determination method is sensitive, specific, accurate, and appropriate for determination of TET in vivo.  Coumarin and/or VO combined with TA can prolong the resistance time of TET significantly, delay elimination and     enhance bioavailability of tetrahydropalmatine.