Synergistic interaction between the Ligusticum chuanxiong constituent butylidenephthalide and the nitric oxide donor sodium nitroprusside in relaxing rat isolated aorta

Ligusticum chuanxiong Hort. (Umbelliferae), a traditional Chinese medicinal herb, is often prescribed together with nitric oxide donors for treating coronary heart diseases such as angina in China; however, studies concerning their pharmacological interaction are scarce. The objective of the present study was to examine the interaction between the Ligusticum chuanxiong major active constituent butylidenephthalide (BDPH) and the nitric oxide donor sodium nitroprusside (SNP) in vasorelaxation. Vasorelaxation was examined in rat isolated aorta using an organ bath system. BDPH and SNP interacted synergistically under 9,11-dideoxy-9α,11α-methanoepoxyprostaglandin H2 (U-46619)-induced tone. This synergism became greater with increasing U-46619 concentrations where Ca2+ sensitization contributed more significantly, and less when U-46619 was replaced with phenylephrine where participation of Ca2+ sensitization was minimal. BDPH-SNP synergism remained intact in the absence of external Ca2+, indicating that regulation of Ca2+ influx was not a requirement for the manifestation of this interaction. The present study demonstrated the synergistic relaxation between BDPH and SNP in rat isolated aorta. This interaction is related to an enhancement of the effectiveness of SNP in producing relaxation under tone induced mainly by Ca2+ sensitization.