Ligusticum wallichii FRANCHAT (or Ligusticum chuanxiong hort; L. wallichii), a member of the Umbelliferaceae family, is a Chinese medicinal herb that is a common constituent in polypharmaceutical herbal drugs. It has been widely used in Asian countries to increase coronary blood flow and systemic circulation, and to relieve stasis. 1,2) Previous studies have indicated that L. wallichii improves blood fluidity 3) and inhibits endothelial cell damage 4) and vascular smooth muscle cell proliferation.
5)We demonstrated that an extract of L. wallichii showed endothelium-dependent acute relaxation in isolated rat thoracic aorta.6) The effect of L. wallichii was due to endothelial nitric oxide (NO). However, the tetramethylpyrazine (TMP)-induced vasorelaxant effect was not related to endothelial NO. TMP was isolated as a biologically active component from L. wallichii. Since 1970, TMP has been used in China for the treatment of patients with angina pectoris and cerebral ischemic syndromes. [7][8][9] Earlier pharmacological studies demonstrated that aortic vasorelaxation induced by TMP involved the opening of ATP-sensitive K ϩ channels and/or small-conductance Ca 2ϩ -activated K ϩ channels. [10][11][12] Endothelium-derived relaxing factor (EDRF) and the membrane potential are major components in modulating vascular tone.13) After EDRF, the most important molecule is probably NO,14,15) and K ϩ channels play an important role in the regulation of membrane potential.16) Five distinct types of K ϩ channel have been documented in arterial smooth muscle: voltage-dependent K ϩ (K V ) channels, large-conductance Ca 2ϩ -activated K ϩ (LK Ca ) channels, small-conductance Ca 2ϩ -activated K ϩ (SK Ca ) channels, inward rectifier K ϩ (K IR ) channels, and ATP-sensitive K ϩ (K ATP ) channels. 16) Additionally, changes in K ϩ channel activity to produce a subsequent alteration in the activity of calcium channels may result in vasorelaxation.17) Thus, the present study was performed to separate the active fraction, to examine the active fractioninduced changes in membrane potential, the possible underlying mechanisms, and to perform comparisons with TMP using isolated endothelium-denuded rat aortic rings.
MATERIALS AND METHODS
Extraction and FractionationDried, sliced L. wallichii was obtained from a local market and ground with a commercial food mixer. The resulting powder was extracted under reflux with absolute ethanol for 1 h. The extract was evaporated under reduced pressure at low temperature (37-40°C) and lyophilized (LwEx). Extracts for all of the experiments were prepared from four batches of L. wallichii to assess variation in individual extracts. LwEx was fractionated successively with water and n-butanol, and each phase was concentrated and lyophilized into water-soluble (LwDw) and butanol-soluble (LwBt) fractions. The solid was stored at Ϫ20°C until use. LwEx and LwBt were dissolved in 30% ethanol and LwDw was dissolved in water to give final concentrations of 0.3 to 3.0 mg/ml in the bath. Voucher specimen nos. Lw-001 (LwE...