Journal of Ethnopharmacology 122 (2009) 308–312 Contents lists available at ScienceDirect Journal of Ethnopharmacology journal homepage: www.elsevier.com/locate/jethpharm Synergistic interaction between the Ligusticum chuanxiong constituent butylidenephthalide and the nitric oxide donor sodium nitroprusside in relaxing rat isolated aorta Sunny Sun-Kin Chan, Robert Leslie Jones, Ge Lin ∗ Department of Pharmacology, Faculty of Medicine, Chinese University of Hong Kong, Hong Kong, China article info Article history: Received 17 January 2008 Received in revised form 8 October 2008 Accepted 1 January 2009 Available online 6 January 2009 Keywords: Ligusticum chuanxiong Synergism Vasorelaxation Butylidenephthalide Sodium nitroprusside Calcium sensitization abstract Ethnopharmacological relevance: Ligusticum chuanxiong Hort. (Umbelliferae), a traditional Chinese medic- inal 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. Aim of the study: The objective of the present study was to examine the interaction between the Ligus- ticum chuanxiong major active constituent butylidenephthalide (BDPH) and the nitric oxide donor sodium nitroprusside (SNP) in vasorelaxation. Materials and methods: Vasorelaxation was examined in rat isolated aorta using an organ bath system. Results: BDPH and SNP interacted synergistically under 9,11-dideoxy-9,11-methanoepoxyprostaglan- din H 2 (U-46619)-induced tone. This synergism became greater with increasing U-46619 concentra- tions where Ca 2+ sensitization contributed more significantly, and less when U-46619 was replaced with phenylephrine where participation of Ca 2+ sensitization was minimal. BDPH-SNP synergism remained intact in the absence of external Ca 2+ , indicating that regulation of Ca 2+ influx was not a requirement for the manifestation of this interaction. Conclusions: 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 Ca 2+ sensitization. © 2009 Elsevier Ireland Ltd. All rights reserved. 1. Introduction Prescribing of an herb–drug combination is a common practice in China. Ligusticum chuanxiong Hort. (Umbelliferae) is a tradi- tional Chinese medicinal herb primarily prescribed for cardio- and cerebro-vascular diseases, menstrual disorders and gynecological problems (Zheng et al., 1997). The herb and its proprietary prod- ucts are often consumed jointly with nitric oxide (NO) donors for treating coronary heart diseases such as angina in China (Zheng et al., 1997). Despite this wide-spread use, the pharmacological inter- actions of Ligusticum chuanxiong and its constituents with other cardiovascular agents have not yet been properly studied. Ligusticum chuanxiong contains various types of ingredients, including phthalides, alkaloids and organic acids. Our previous reports showed that butylidenephthalide (BDPH, Fig. 1) is a major Ligusticum chuanxiong bioactive constituent and an effective vasorelaxant (Li et al., 2003; Yan et al., 2005; Chan et al., 2006a). BDPH also has anti-anginal and platelet-inhibitory actions and is ∗ Corresponding author. Tel.: +852 2609 6824; fax: +852 2603 5139. E-mail address: linge@cuhk.edu.hk (G. Lin). postulated to be a major contributor to the therapeutic effects of Ligusticum chuanxiong (Teng et al., 1987; Ko et al., 1994, 1998b; Lin et al., 2006; Chan et al., 2008). The vasorelaxation mechanism of BDPH involves suppression of several transduction processes, including voltage- and receptor- mediated Ca 2+ influx, Ca 2+ release from internal stores, and protein kinase C- and Rho kinase-mediated Ca 2+ sensitization (Ko et al., 1998a, 2002; Chan et al., 2006a). During our studies on BDPH, we observed a clear synergism between BDPH and the NO donor sodium nitroprusside (SNP) in relaxing rat isolated aorta, which may serve as the rationale behind the frequent use of a Ligusticum chuanxiong–NO donor combination in China. The current paper describes our attempts to characterize this synergism and to exam- ine the mechanisms involved. 2. Materials and methods 2.1. Materials BDPH was purchased from Aldrich Chemicals (St. Louis, MO, USA). 9,11-Dideoxy-9,11-methanoepoxyprostaglandin H 2 (U-46619) was purchased from Sapphire Bioscience (Redfern, 0378-8741/$ – see front matter © 2009 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.jep.2009.01.002