Inhibitory effects of potassium channel blockers on tetramethylpyrazine-induced relaxation of rat aortic strip in vitro

Bibliometric analysis of research progress on tetramethylpyrazine and its effects on ischemia-reperfusion injury

In recent decades, natural products have attracted worldwide attention and become one of the most important resources for pharmacological industries and medical sciences to identify novel drug candidates for disease treatment. Tetramethylpyrazine (TMP) is an alkaloid extracted from Ligusticum chuanxiong Hort., which has shown great therapeutic potential in cardiovascular and cerebrovascular diseases, liver and renal injury, as well as cancer. In this review, we analyzed 1270 papers published on the Web of Science Core Collection from 2002 to 2022 and found that TMP exerted significant protective effects on ischemia-reperfusion (I/R) injury that is the cause of pathological damages in a variety of conditions, such as ischemic stroke, myocardial infarction, acute kidney injury, and liver transplantation. TMP is limited in clinical applications to some extent due to its rapid metabolism, a short biological half-life and poor bioavailability. Obviously, the structural modification, administration methods and dosage forms of TMP need to be further investigated in order to improve its bioavailability. This review summarizes the clinical applications of TMP, elucidates its potential mechanisms in protecting I/R injury, provides strategies to improve bioavailability, which presents a comprehensive understanding of the important compound. Hopefully, the information and knowledge from this review can help researchers and physicians to better improve the applications of TMP in the clinic.

An Overview of Tetramethylpyrazine (Ligustrazine) and its Derivatives as Potent Anti-Alzheimer’s Disease Agents

Abstract:

Tetramethylpyrazine (TMP), or ligustrazine, is an alkaloid isolated from the Chinese herb Ligusticum wallichii. It is known for its broad-spectrum medicinal properties against several diseases, and various studies have shown that it can modulate diverse biological targets and signaling pathways to produce neuroprotective effects, especially against Alzheimer’s disease (AD). This has attracted significant research attention evaluating TMP as a potent multitarget anti-AD agent. This review compiles the results of studies assessing the neuroprotective mechanisms exerted by TMP as well as its derivatives prepared using a multi-target-directed ligand strategy to explore its multitarget modulating properties. The present review also highlights the work done on the design, synthesis, structure-activity relationships, and mechanisms of some potent TMP derivatives that have shown promising anti-AD activities. These derivatives were designed, synthesized, and evaluated to develop anti-AD molecules with enhanced biological and pharmacokinetic activities compared to TMP. This review article paves the way for the exploration and development of TMP and TMP derivatives as an effective treatment for AD.

The Role of Traditional Chinese Herbal Medicines and Bioactive Ingredients on Ion Channels: A Brief Review and Prospect

Traditional Chinese Medicines (TCMs), particularly the Chinese herbal medicines, are valuable sources of medicines and have been used for centuries. The term "TCMs" both represents to the single drug agent like Salvia miltiorrhiza, Ligusticum chuanxiong and Angelica sinensis, and those herbal formulas like Jingshu Keli, Wenxin Keli and Danzhen powder. In recent years, the researches of TCMs developed rapidly to understand the scientific basis of these herbs. In this review, we collect the studies of TCM and their containing bioactive compounds, and attempt to provide an overview for their regulatory effects on different ion channels including Ca2+, K+, Na+, Cl- channels and TRP, P2X receptors. The following conditions are used to limit the range of our review. (i) Only the herbal materials are included in this review and the animal- and mineral-original TCMs are excluded. (ii) The major discussions in this review focus on single TCM agent and the herbal formulas are only discussed for a little. (iii) Those most famous herbal medicines like Capsicum annuum (pepper), Curcuma longa (ginger) and Cannabis sativa (marijuana) are excluded. (iv) Only those TCM herbs with more than 5 research papers confirming their effects on ion channels are discussed in this review. Our review discusses recently available scientific evidences for TCMs and related bioactive compounds that have been reported with the modulatory effects on different ion channels, and thus provides a new ethnopharmacological approach to understand the usage of TCMs.

The Preparation of Novel Ligustrazine Derivatives as Potential Cerebrocardiac Vascular Agents

A series of novel substituted cinnamoylpiperazinyl ligustrazine derivatives 7 has been prepared by alkylation of cinnamoylpiperazines by (chloromethyl)trimethylpyrazine (5) or by cinnamoylation of trimethyl(piperazinomethyl) pyrazine (6).

Protection of dilator function of coronary arteries from homocysteine by tetramethylpyrazine: Role of ER stress in modulation of BKCa channels

OBJECTIVES

We recently reported the involvement of ER stress-mediated BK_Ca channel inhibition in homocysteine-induced coronary dilator dysfunction. In another study, we demonstrated that tetramethylpyrazine (TMP), an active ingredient of the Chinese herb Chuanxiong, possesses potent anti-ER stress capacity. The present study investigated whether TMP protects BK_Ca channels from homocysteine-induced inhibition and whether suppression of ER stress is a mechanism contributing to the protection. Furthermore, we explored the signaling transduction involved in TMP-conferred protection on BK_Ca channels.

METHODS

BK_Ca channel-mediated relaxation was studied in porcine small coronary arteries. Expressions of BK_Ca channel subunits, ER stress molecules, and E3 ubiquitin ligases, as well as BK_Ca ubiquitination were determined in porcine coronary arterial smooth muscle cells (PCASMCs). Whole-cell BK_Ca currents were recorded.

RESULTS

Exposure of PCASMCs to homocysteine or the chemical ER stressor tunicamycin increased the expression of ER stress molecules, which was significantly inhibited by TMP. Suppression of ER stress by TMP preserved the BK_Ca β1 protein level and restored the BK_Ca current in PCASMCs, concomitant with an improved BK_Ca-mediated dilatation in coronary arteries. TMP attenuated homocysteine-induced BK_Ca β1 protein ubiquitination, in which inhibition of ER stress-mediated FoxO3a activation and FoxO3a-dependent atrogin-1 and Murf-1 was involved.

CONCLUSIONS

Reversal of BK_Ca channel inhibition via suppressing ER stress-mediated loss of β1 subunits contributes to the protective effect of TMP against homocysteine on coronary dilator function. Inhibition of FoxO3a-dependent ubiquitin ligases is involved in TMP-conferred normalization of BK_Ca β1 protein level. These results provide new mechanistic insights into the cardiovascular benefits of TMP.

Effects of tetramethylpyrazine phosphate on pancreatic islet microcirculation in SD rats

PURPOSES

Abnormal islet microcirculation impetus the insulin production and accelerates progression of Type 1 and 2 diabetes. In this study, we investigated whether tetramethylpyrazine phosphate (TMPP), a vasoactive substance, could regulate the islet microcirculation and insulin concentration and improve glycaemia in SD rats.

METHODS

SD rats were randomly divided into two groups, the control and TMPP groups. Each group was further divided into three subgroups according to the intravenous injection of either saline, 15 or 30% glucose. The non-radioactive microsphere technique was adopted to measure the organ blood flow. Nitric oxide synthase (NOS) blocker L-NAME was used to address whether NO was involved in mediating the vasoactive effects of TMPP.

RESULTS

In the TMPP group, TMPP increased the PBF (pancreatic blood flow), IBF (islet blood flow), and fIBF (fraction of islet blood flow out of pancreatic blood flow) by 57, 76 and 47%, respectively, after 30% glucose infusion, compared with the control, indicating that TMPP could regulate islet microcirculation. Furthermore, TMPP induced a 66% elevation of IBF and 37% of fIBF in the 30% glucose subgroups than the 15% ones. In 30% glucose-treated subgroups, TMPP improved the blood glucose concentration by 10%, compared with the control (19.3 ± 0.64 vs 17.32 ± 0.56 mmol/l, P < 0.05), without influencing the insulin secretion. Blocking NO formation prevented the enhanced PBF and IBF, evoking by TMPP with 30% glucose.

CONCLUSIONS

TMPP can regulate the pancreatic islet microcirculation and possess a hypoglycemia effect after glucose infusion through affecting the islet microcirculation.

Efficacy of Suxiao Jiuxin Pill on Coronary Heart Disease: A Meta-Analysis of Randomized Controlled Trials

Suxiao jiuxin pill is considered an effective ancillary drug in patients with coronary heart disease. Although numerous small, single-center clinical trials have been conducted, the benefits and harms of suxiao jiuxin pill remain controversial. We performed a meta-analysis to clarify the efficacy of suxiao jiuxin pill on patients with coronary heart disease. Randomized controlled trials were identified by using the Cochrane Library, PubMed, Web of Science, Embase, Wanfang, Weipu, and China Knowledge Resource Integrated databases (until June 2016). Pooled relative risks (RR), weighted mean differences (WMD), and 95% confidence intervals (95% CIs) were estimated using random-effects models. Forty-one trials involving 6276 patients were included in our analysis. Administration of suxiao jiuxin pill significantly improved electrocardiogram (ECG) results when compared with other therapies (RR 1.32, 95% CI 1.26 to 1.38, and P < 0.001). Subgroup analyses revealed that suxiao jiuxin pills improve ECG results more than salvia tablets (RR 1.54, 95% CI 1.41 to 1.67, and P < 0.001), isosorbide dinitrate (RR 1.14, 95% CI 1.21 to 1.44, and P = 0.001), nitroglycerin (RR 1.35, 95% CI 1.16 to 1.56, and P < 0.001), and other drugs (RR 1.32, 95% CI 1.21 to 1.44, and P < 0.001). Available evidence additionally suggests that suxiao jiuxin pills could significantly reduce total cholesterol (WMD −0.62 mmol/L, 95% CI −1.06 to –0.18 mmol/L, and P = 0.005) and low-density lipoprotein (LDL) levels (WMD −1.12 mmol/L, 95% CI −1.42 to −0.82 mmol/L, and P < 0.001) and increase high-density lipoprotein (HDL) levels (WMD 0.32 mmol/L, 95% CI 0.07 to 0.58 mmol/L, and P = 0.014). However, no significant differences were observed in total triglyceride levels, plasma viscosity, hematocrit, and fibrinogen. No incidences of adverse reactions were observed after administration of suxiao jiuxin pill. Improvements in ECG results and lipid profiles were also observed after suxiao jiuxin administration compared to other therapies. It also decreased low-cut and high-cut whole blood viscosity without significant adverse reactions.

A systematic review on the rhizome of Ligusticum chuanxiong Hort. (Chuanxiong)

Chuanxiong Rhizome (called Chuanxiong, CX in Chinese), the dried rhizome of Ligusticum chuanxiong Hort, is an extremely common traditional edible-medicinal herb. As a widely used ethnomedicine in Asia including China, Japan and Korea, CX possesses ideal therapeutic effect on cardiovascular and cerebrovascular diseases, and is also used as a major ingredient in soups for regular consumption to benefit health. Based on the traditional perception, amounts of investigations on different aspects have been done for CX in the past decades. However, no literature systematic review about these achievements have been compiled. Herein, the aim of this review is to present the up-to-date information on the ethnobotany, ethnopharmacological uses, phytochemicals, pharmacological activities, toxicology of this plant to identify their therapeutic potential and directs future research opportunities. So far, about 174 compounds has been isolated and identified from CX, in which phthalides and alkaloids would be the main bioactive ingredients for its pharmacological properties, such as anti-cerebral ischemia, anti-myocardial ischemia, blood vessel protection, anti-thrombotic, anti-hypertensive, anti-atherosclerosis, anti-spasmodic, anti-inflammatory, anti-cancer, anti-oxidant, and anti-asthma effects. Even so, due to the incomplete standardized planting, unstable herbal quality, and outdated preparation techniques, the industrial progress of CX is still less developed.

Locally and traditionally used Ligusticum species - A review of their phytochemistry, pharmacology and pharmacokinetics

ETHNOPHARMACOLOGICAL RELEVANCE

Ligusticum species (Umbelliferae) have been widely used in traditional Chinese medicine, Korean folk medicine and Native American medicine for their medicinal and nutritional value. Decoctions of the rhizomes are used in treatment and prophylaxis of migraine, anemia and cardiovascular conditions including stroke.

AIM OF STUDY

This review is intended to fully compile the constituents of locally and traditionally used Ligusticum species, present their bioactivities and highlight potential leads for future drug design, and thus, provide a reference for further research and application of these species. Emphasis is also placed on current trends in the pharmacokinetic studies of the major constituents.

METHODS

The literature discussed is derived from readily accessible papers spanning the early 1990s to the end of 2015. Information was collected from journals, books and online searches (Google Scholar, PubMed, ScienceDirect, SciFinder, Springerlink and CNKI).

RESULTS

The major phytoconstituents, 154 of which are presented in this review, include alkaloids, phthalides and phenolic acids. The crude extracts and isolated constituents have exhibited a wide range of in vitro and in vivo pharmacologic effects, including cardioprotective, antioxidant, anti-inflammatory and neuroprotective activities. The bioactive alkaloid tetramethylpyrazine (TMP) has attracted the most attention for its potent effect on calcium channels, anti-platelet as well as anti-inflammatory effects. Pharmacokinetic studies of major constituents have also been summarized.

CONCLUSION

The pthalides, organic acids and alkaloids of Ligusticum species have emerged as a good source of traditional medicines for the management of cardio- and cerebrovascular conditions, inflammation and neurogenerative disorders. The species discussed in this review have demonstrated wide pharmacological actions and have great potential to yield multipotent drugs if challenges such as poor bioavailability, solubility and toxicological profiles are addressed. Apart from the rhizomes, pharmacological activities of other botanical parts also need to be studied further. Expansion of research to cover other species in the Ligusticum genus would provide more opportunities for the discovery of new bioactive principles.

Characterization of imidazoline receptors in blood vessels for the development of antihypertensive agents

It has been indicated that activation of peripheral imidazoline I2-receptor (I-2R) may reduce the blood pressure in spontaneously hypertensive rats (SHRs). Also, guanidinium derivatives show the ability to activate imidazoline receptors. Thus, it is of special interest to characterize the I-2R using guanidinium derivatives in blood vessels for development of antihypertensive agent(s). Six guanidinium derivatives including agmatine, amiloride, aminoguanidine, allantoin, canavanine, and metformin were applied in this study. Western blot analysis was used for detecting the expression of imidazoline receptor in tissues of Wistar rats. The isometric tension of aortic rings isolated from male rats was also estimated. The expression of imidazoline receptor on rat aorta was identified. However, guanidinium derivatives for detection of aortic relaxation were not observed except agmatine and amiloride which induced a marked relaxation in isolated aortic rings precontracted with phenylephrine or KCl. Both relaxations induced by agmatine and amiloride were attenuated by glibenclamide at concentration enough to block ATP-sensitive potassium (KATP) channels. Meanwhile, only agmatine-induced relaxation was abolished by BU224, a selective antagonist of imidazoline I2-receptors. Taken together, we suggest that agmatine can induce vascular relaxation through activation of peripheral imidazoline I2-receptor to open KATP channels. Thus, agmatine-like compound has the potential to develop as a new therapeutic agent for hypertension in the future.

Suxiao jiuxin pill induces potent relaxation and inhibition on contraction in human artery and the mechanism

Suxiao Jiuxin Pill, a compound Chinese traditional medicine with main components of tetramethylpyrazine and borneol, is widely used for antiangina treatment in China but its pharmacological effect on human blood vessels is unknown. We investigated the effect and possible mechanism of SJP in the human internal mammary artery (IMA, n = 78) taken from patients undergoing coronary surgery. SJP caused full relaxation in KCl- (99.4 ± 10.5%, n = 6) and U46619- (99.9 ± 5.6%, n = 6) contracted IMA. Pretreatment of IMA with plasma concentrations of SJP (1 mg/mL), calculated from the plasma concentration of its major component borneol, significantly depressed the maximal contraction to KCl (from 35.8 ± 6.0 mN to 12.6 ± 5.6 mN, P = 0.03) and U46619 (from 19.4 ± 2.9 mN to 5.7 ± 2.4 mN, P = 0.007) while SJP at 10 mg/mL abolished the subsequent contraction. Endothelium denudation and inhibition of eNOS significantly altered the SJP-induced relaxation without changes of eNOS expression. We conclude that SJP has a potent inhibitory effect on the vasoconstriction mediated by a variety of vasoconstrictors in human arteries. The vasorelaxation involves both endothelium-dependent and -independent mechanisms. Thus, the effect of SJP on human arteries demonstrated in this study may prove to be particularly important in vasorelaxing therapy in cardiovascular disease.

Phenols, Alkaloids and Terpenes from Medicinal Plants with Antihypertensive and Vasorelaxant Activities. A Review of Natural Products as Leads to Potential Therapeutic Agents

Numerous studies support the cardiovascular effects of medicinal plants. This review examines plants whose antihypertensive and vasorelaxant effects have been scientifically validated. Our study selected only chemically characterized plants whose mode of action had already been investigated. The aim of the paper is to provide a quick way to identify medicinal plants and their constituents with antihypertensive and vasorelaxant activities.

Changes of imidazoline receptors in spontaneously hypertensive rats

The role of imidazoline receptors in the regulation of vascular function remains unclear. In this study, we evaluated the effect of agmatine, an imidazoline receptor agonist, on systolic blood pressure (SBP) in spontaneously hypertensive rats (SHRs) and investigated the expressions of imidazoline receptors by Western blot. The isometric tension of aortic rings isolated from male SHRs was also estimated. Agmatine decreased SBP in a dose-dependent manner in SHRs but not in the normal group [Wistar-Kyoto (WKY) rats]. This reduction in SBP in SHRs was abolished by BU224, a selective antagonist of imidazoline I(2) -receptors. Higher expression of imidazoline receptors in SHR was observed. Moreover, agmatine-induced relaxation in isolated aortic rings precontracted with phenylephrine or KCl. This relaxation was also abolished by BU224 but was not modified by efaroxan, an imidazoline I(1) -receptor antagonist. Agmatine-induced relaxation was also attenuated by PNU 37883, a selective blocker of vascular ATP-sensitive potassium (K(ATP) ) channels. Additionally, vasodilatation by agmatine was reduced by an inhibitor of protein kinase A (PKA). We suggest that agmatine can lower blood pressure in SHRs through activation of the peripheral imidazoline I(2) -receptor, which is expressed more highly in SHRs.

Interaction of tetramethylpyrazine with two serum albumins by a hybrid spectroscopic method

The interactions of tetramethylpyrazine (TMPZ) with bovine serum albumin (BSA) and human serum albumin (HSA) have been investigated by various spectroscopic techniques. Fluorescence tests showed that TMPZ could bind to BSA/HSA to form complexes. The binding constants of TMPZ-BSA and TMPZ-HSA complexes were observed to be 1.442 × 10(4) and 3.302 × 10(4)M(-1) at 298K, respectively. The thermodynamic parameters (ΔG, ΔH and ΔS) calculated on the basis of different temperatures revealed that the binding of TMPZ-HSA was mainly depended on hydrophobic interaction, and yet the binding of TMPZ-BSA might involve hydrophobic interaction strongly and electrostatic interaction. The results of synchronous fluorescence, three-dimensional fluorescence, UV-vis absorption, FT-IR and CD spectra showed that the conformations of both BSA and HSA altered with the addition of TMPZ. The binding average distance between TMPZ and BSA/HSA was evaluated according to Föster non-radioactive energy transfer theory. In addition, with the aid of site markers (such as, phenylbutazone, ibuprofen and digitoxin), TMPZ primarily bound to tryptophan residues of BSA/HSA within site I (sub-domain II A).

Ligusticum chuanxiong Hort: a review of chemistry and pharmacology

CONTEXT

Ligusticum chuanxiong Hort (LC; Umbelliferae) is an effective medical plant, which has been extensively applied for many years to treat various diseases with other Chinese herbal medicines. Although a considerable amount of scientific research was reported on LC in the last decade, it is currently scattered across various publications. The present review comprises the chemical and pharmacological research on LC in the last decade.

OBJECTIVE

The objective of this review is to bring together most of the scientific research available on LC and evaluate its effects and mechanisms.

METHODS

The information for 82 cases included in this review was compiled using major databases such as Medline, Elsevier, Springer, Pubmed, and Scholar.

RESULTS

The compounds contained in LC can be divided into five kinds, essential oil (EO), alkaloids, phenolic acids, phthalide lactones, and other constituents. A great deal of pharmacological research has been done, which mainly focuses on cardiovascular and cerebrovascular effects, antioxidation, neuroprotection, antifibrosis, antinociception, antiinflammation, and antineoplastic activity.

CONCLUSION

A large number of pharmacological and chemical studies during the last 10 years have demonstrated the vast medicinal potential of LC. It is still very clear that LC is a plant with widespread use now and also with extraordinary potential for the future. The documents strongly support the view that LC has beneficial therapeutic properties and indicates its potential as an effective adaptogenic herbal remedy.

Ligustrazine inhibits lipopolysaccharide-induced proliferation by affecting P27, Bcl-2 expression in rat mesangial cells

Ligustrazine has a renoprotective effect against nephritis. In the present study, we investigated the roles of ligustrazine on lipopolysaccharide-induced changes of proliferation, cell cycle in cultured rat mesangial cells. 3-(4,5-dimethyltiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay revealed that rat mesangial cells treated with lipopolysaccharide (10mg/l) underwent significant proliferation compared with control group. This effect was significantly inhibited by ligustrazine (400 to 2500 mg/l). Flow cytometric analysis revealed that cells treated with lipopolysaccharide showed significant reduction in the ratio of G0/G1 phase and significant elevation in the ratio of S+G2/M phase. The changes of cell cycle induced by lipopolysaccharide were reversed by ligustrazine. In addition, lipopolysaccharide suppressed P27 protein expression was significantly increased by ligustrazine (100, 500, 2500 mg/l). Moreover, rat mesangial cells treated with lipopolysaccharide showed scanty apoptosis with up-regulation of Bcl-2expression, while Bax protein expression was not changed. Ligustrazine (100, 500, 2500 mg/l) significantly reversed lipopolysaccharide-induced up-regulation of Bcl-2 protein and increased apoptotic cell death. In summary, ligustrazine displayed a significant inhibiting effect on lipopolysaccharide-induced proliferation through increasing P27 and decreasing Bcl-2 protein expression in rat mesangial cells.

Activation of peripheral opioid µ-receptors in blood vessel may lower blood pressure in spontaneously hypertensive rats

BACKGROUND/AIMS

The role of opioid receptors in the regulation of vascular function remains unclear. In the current study, we evaluated the ability of loperamide, a peripheral opioid receptor agonist, to regulate blood pressure in spontaneously hypertensive rats (SHRs) and examined the mechanism(s) by which loperamide exerts its effects.

METHODS

In male SHRs, mean arterial pressure (MAP) was measured and hemodynamic analysis was recorded. Additionally, the isometric tension of aortic rings isolated from SHRs was determined.

RESULTS

Loperamide dose-dependently decreased MAP in SHRs but not in the normal group of Wistar-Kyoto rats. This reduction of MAP in conscious SHRs was abolished by the selective opioid μ-receptor antagonist cyprodime, but not by naloxonazine, the μ(1)-opioid receptor antagonist. However, cardiac output was not altered by loperamide in anesthetized SHRs. Moreover, loperamide-induced relaxation in isolated aortic rings precontracted with phenylephrine or vasopressin. This relaxation was abolished by cyprodime, but not by naloxonazine. Loperamide-induced relaxation was also attenuated by glibenclamide, an ATP-sensitive potassium (K(ATP)) channel blocker. Additionally, vasodilatation by loperamide was reduced by an inhibitor of protein kinase A (PKA) and enhanced by an inhibitor of phosphodiesterases.

CONCLUSION

We suggest that loperamide can lower MAP in SHRs via μ(2)-opioid receptor-dependent cAMP-PKA pathway that induces vascular relaxation by opening K(ATP) channels.

Prostatic relaxation induced by loperamide is mediated through activation of opioid μ-2 receptors in vitro

The merit of opioid μ-receptor activation in the improvement of benign prostatic hyperplasia (BPH) remains obscure. In the present study, we used loperamide to identify the subtype of opioid μ-receptors involved in prostatic relaxation and investigate the possible mechanism of this relaxation. Prostate strips were isolated from 12-week-old male Wistar rats for identification of isometric tension. The prostate strips were precontracted with either 1 μmol/l phenylephrine or 50 mmol/l KCl. The decrease in muscle tone (relaxation) was then characterized after cumulative administration of loperamide (0.1 to 10 μmol/l) into the organ bath for the concentration-dependent study. Pretreatment with specific blockers or antagonists was carried out to compare the changes in loperamide-induced relaxation. Loperamide produced a marked relaxation in the isolated prostates precontracted with phenylephrine or KCl in a dose-dependent manner. This relaxation was abolished by cyprodime, a selective opioid μ-receptor antagonist, but was not modified by naloxonazine at a dose sufficient to block the opioid μ-1 receptors. Treatment with an agonist for opioid μ-1 receptors also failed to modify the muscle tone. Moreover, the relaxation by loperamide was attenuated by glibenclamide at a dose sufficient to block ATP-sensitive K(+) channels. In addition, this action of loperamide was abolished by protein kinase A (PKA) inhibitor and enhanced by the inhibitor of phosphodiesterase for cyclic AMP (cAMP). Our results suggest that loperamide induces prostatic relaxation through activation of opioid μ-2 receptors via the cAMP-PKA pathway to open ATP-sensitive K(+) channels.

Antihypertension Induced by Tanshinone IIA Isolated from the Roots of Salvia miltiorrhiza

Tanshinone IIA is one of the active principles in danshen (Salvia miltiorrhiza Bge) widely used in treatment of cardiovascular disorders. We investigated the effect of danshen or tanshinone IIA on blood pressure and its possible mechanisms. An i.p. injection of danshen at 10 mg kg(-1) significantly lowered systolic blood pressure (SBP) of spontaneously hypertensive rats (SHRs) but failed to modify the SBP in normotensive Wistar-Kyoto rats (WKY). Oral administration of tanshinone IIA also decreased SBP in SHR but not in WKY. Tanshinone IIA produced a concentration-dependent relaxation in isolated SHR aortic rings precontracted with phenylephrine (10 nmol l(-1)) or potassium chloride (KCl) (40 mmol l(-1)). The relaxing effect of tanshinone IIA on tonic contraction of phenylephrine in isolated aortic rings without endothelium remained produced. Glibenclamide at concentration sufficient to block adenosine triphosphatase (ATP)-sensitive potassium (K(+)) channel attenuated this tanshinone IIA-induced relaxation that was not influenced by other inhibitors. We further investigated the effect of tanshinone IIA on the changes of intracellular calcium concentration ([Ca(2+)](i)) in cultured aortic smooth muscle (A7r5) cells using fura-2 as indicator. Tanshinone IIA decreased [Ca(2+)](i) elicited by phenylephrine (10 nmol l(-1)) or KCl (40 mmol l(-1)) in a concentration-dependent manner; glibenclamide, but not other inhibitors for K(+) channel, abated this effect. Our results suggest that tanshinone IIA acts as an active principle of danshen showing vasodilation through ATP-sensitive K(+) channel to lower [Ca(2+)](i).

Endothelium-independent vasorelaxation by Ligusticum wallichii in isolated rat aorta: comparison of a butanolic fraction and tetramethylpyrazine, the main active component of Ligusticum wallichii

Ligusticum wallichii is an herb widely used to treat vascular disorders in Asian countries, and tetramethylpyrazine (TMP) has been identified as one of its vasorelaxant active components. This study was performed to examine the endothelium-independent relaxation produced by the butanol-soluble fraction of L. wallichii extract (LwBt) and its possible mechanisms of action in isolated rat aortic rings. The effects were compared with those of TMP. LwBt produced vasorelaxation that increased gradually after 2-3 min of LwBt administration and reached a maximum within 30 min. LwBt-induced relaxation was significantly attenuated by pretreatment with 4-aminopyridine and apamin. Additionally, LwBt attenuated CaCl(2)-induced vasoconstriction in high-potassium depolarized medium. Thus, LwBt-induced vasorelaxation apparently involved inhibition of calcium influx, mediated by the opening of voltage-dependent and/or Ca(2+)-activated potassium channels. On the other hand, the effect of TMP was significantly attenuated by pretreatment with glibenclamide, and 4-aminopyridine had no effect. In conclusion, LwBt-induced endothelium-independent vasorelaxation was mediated by the opening of voltage-dependent potassium channels, while TMP-induced relaxation was mediated by the opening of ATP-dependent potassium channels. These effects of LwBt may be due to a substance other than TMP.

Synergistic vasorelaxant and antihypertensive effects of Ligusticum wallichii and Angelica gigas

AIM OF THE STUDY

The synergistic vasorelaxant and antihypertensive effects of Ligusticum wallichii and Angelica gigas were examined in isolated rat aorta rings and spontaneously hypertensive rats (SHRs).

MATERIALS AND METHODS

The ethanol extract of Ligusticum wallichii (LwEx) or Angelica gigas (AgEx) or their combinations at ratios Ligusticum wallichii:Angelica gigas = 1:1 (MxEx11), 1:3 (MxEx13), and 3:1 (and MxEx31), and their successive water soluble (LwDw, AgDw, MxDw11, MxDw13 and MxDw31) or n-butanol soluble fractions (LwBt, AgBt, MxBt11, MxBt13, and MxBt31) were examined for their vasorelaxant effects. In an antihypertensive study, LwEx, AgEx, or MxEx11 (100 mg/kg) was orally administered to SHRs, and the systolic, diastolic, and mean blood pressure were measured using the tail-cuff method before and 1, 3, 5, 7, and 24 h after oral administration.

RESULTS

Each of the ethanol extracts caused long-term relaxation in endothelium-intact or endothelium-denuded rat aorta preconstricted with norepinephrine (NE, 300 nM). All of the water phases of the ethanol extracts elicited an endothelium-dependent acute relaxation, and the water phase of MxDw11 (EC50 values: 1.08 mg/mL, P < 0.05) had the highest activity. MxDw11-induced acute relaxation was abolished by pretreatment with N(G)-nitro-L-arginine (10 microM), methylene blue (1.0 microM), or atropine (0.1 microM), indicating that the response to MxDw involves the enhancement of the nitric oxide-cGMP system. On the other hand, all of the butanol phases showed an endothelium-independent long-term relaxation, and MxBt11 (85 +/- 7% relaxation of NE-preconstricted active tone at 20 min after the addition, P < 0.05) displayed the highest activity. MxBt11-induced gradual relaxation was significantly attenuated by an inward rectifier potassium-channel inhibitor, but not by an ATP-sensitive or a large conductance Ca2+-activated potassium-channel blocker. Calcium concentration-dependent contraction curves in high-potassium, depolarizing medium were shifted significantly to the right and downward after incubation with MxBt11 (0.03, 0.1, and 0.3 mg/mL), implying that MxBt11 is also involved in the inhibition of extracellular calcium influx to vascular smooth muscle. MxEx11 (100 mg/kg) significantly reduced systolic blood pressure of SHRs at 3, 5, and 7 h after oral administration, but this effect was not induced by Ligusticum wallichii or Angelica gigas alone.

CONCLUSIONS

The combination of Ligusticum wallichii and Angelica gigas elicits a synergistic effect on vasorelaxation in isolated rat aortas and antihypertension in SHRs. The ratio of Ligusticum wallichii: Angelica gigas = 1:1 was the most effective of all combinations tested.

Protective effects of ligustrazine on cisplatin-induced oxidative stress, apoptosis and nephrotoxicity in rats

Cisplatin is an effective agent against various solid tumors. However, its nephrotoxicity been reported to be a dose-limiting factor for treating various types of tumors. The aim of this study was to determine the protective effects of ligustrazine on cisplatin-induced nephrotoxicity through tissue oxidant/antioxidant parameters, light microscopic evaluation, and tubular apoptosis in rats. Ligustrazine was administered in doses of 50 and 100mg/kg/day intraperitoneally (i.p.), for 7 consecutive days, starting 2 days before a single intraveneous dose of cisplatin (8mg/kg). Results revealed that treatment with cisplatin alone caused significant changes in the levels of urinary protein, urinary N-acetyl-beta-d-glucosaminidase, serum creatinine, blood urea nitrogen, and kidneys histopathological damages. All the aforementioned changes were effectively attenuated by ligustrazine. In addition, cisplatin caused increases in the levels of malondialdehyde, nitric oxide, nitric oxide synthase and decreases in the levels of reduced glutathione, glutathione-S-transferase, superoxide dismutase. These changes were restored to near normal levels by ligustrazine at 100mg/kg. In conclusion, ligustrazine has dose dependent protective effects against cisplatin-induced renal tubular toxicity.

Tetramethylpyrazine inhibits angiotensin II-increased NAD(P)H oxidase activity and subsequent proliferation in rat aortic smooth muscle cells

Tetramethylpyrazine (TMP) is the major component extracted from the Chinese herb, Chuanxiong, which is widely used in China for the treatment of cardiovascular problems. The aims of this study were to examine whether TMP may alter angiotenisn II (Ang II)-induced proliferation and to identify the putative underlying signaling pathways in rat aortic smooth muscle cells. Cultured rat aortic smooth muscle cells were preincubated with TMP and then stimulated with Ang II, [3H]-thymidine incorporation and the ET-1 expression was examined. Ang II increased DNA synthesis which was inhibited by TMP (1-100 microM). TMP inhibited the Ang II-induced ET-1 mRNA levels and ET-1 secretion. TMP also inhibited Ang II-increased NAD(P)H oxidase activity, intracellular reactive oxygen species (ROS) levels, and the ERK phosphorylation. Furthermore, TMP and antioxidants such as Trolox and diphenylene iodonium decreased Ang II-induced ERK phosphorylation, and activator protein-1 reporter activity. In summary, we demonstrate for the first time that TMP inhibits Ang II-induced proliferation and ET-1, partially by interfering with the ERK pathway via attenuation of Ang II-increased NAD(P)H oxidase and ROS generation. Thus, this study delivers important new insight in the molecular pathways that may contribute to the proposed beneficial effects of TMP in cardiovascular disease.

VASODILATATION INDUCED BY SINOMENINE LOWERS BLOOD PRESSURE IN SPONTANEOUSLY HYPERTENSIVE RATS

1. Sinomenine is an alkaloid with a wide range of pharmacological actions. In the present study, we investigated the effect of sinomenine on blood pressure and its possible mechanisms of action. 2. Spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats were given intraperitoneal injections of sinomenine. At 30 min, 2.5-10 mg/kg sinomenine decreased systolic blood pressure (SBP) in a dose-dependent manner in SHR, but had no effect on the SBP in WKY rats. 3. The vascular effect of sinomenine was then examined in aortic rings isolated from Wistar rats. Sinomenine (0.1-10 micromol/L) produced concentration-dependent relaxation in aortic rings precontracted with phenylephrine (10 nmol/L) or KCl (40 mmol/L). Glibenclamide (1-100 micromol/L), a specific inhibitor of ATP-sensitive K(+) channels attenuated the sinomenine-induced relaxation, but this effect was not observed when inhibitors of other types of K(+) channels were used. 4. We further investigated the effects of sinomenine on changes in intracellular Ca(2+) concentrations ([Ca(2+)](i)) in cultured aortic smooth muscle (A7r5) cells by using the Ca(2+)-sensitive dye fura-2 as an indicator. Sinomenine, over the concentration range 0.1-10 micromol/L, decreased the increases in [Ca(2+)](i) elicited by phenylephrine (1 micromol/L) or KCl (40 mmol/L) in a concentration-dependent manner. Glibenclamide (1-100 micromol/L) abolished the effects of sinomenine. 5. In conclusion, sinomenine causes vascular relaxation by opening ATP-sensitive K(+) channels, thus decreasing [Ca(2+)](i).

A systematic review of mechanisms by which natural products of plant origin evoke vasodilatation

This article reviews the body of work aimed at elucidating the mechanisms of action by which natural products of plant origin exert a vasodilatory effect at the level of the vasculature. The search was restricted to 4 mechanisms: the nitric oxide system and (or) reactive oxygen species, the eicosanoid system, potassium channel function, and calcium channel function. The National Library of Medicine database was searched using "PubMed" without restriction to language. The search generated 266 references on 15 November 2005. Most studies were in vitro in nature and of these, most involved studies in the rat aorta. Many of the natural products evoked vasodilatation through an endothelium-dependent mechanism. The vasodilatation was attenuated or abolished by a nitric oxide synthase inhibitor and, in some of these studies, by an inhibitor of guanylate cyclase. A few studies reported a cyclooxygenase component, but most found no effect of the cyclooxygenase inhibitor, indomethacin. The vasorelaxation evoked by several natural products was attenuated by various potassium channel blocking agents, suggesting that some natural products exerted their effect either directly or indirectly through activation of potassium channels. Finally, a significant number of natural products evoked vasodilatation either through blockade of calcium channels or by inhibiting the release of calcium from intracellular stores. Many natural products evoked vasodilatation through multiple mechanisms. The information in this review on mechanisms of action should facilitate good clinical practice by increasing the predictive capabilities of the practitioner, notably the ability to predict adverse effects and interactions among medications. The knowledge should also help to provide leads to the ultimate goal of developing new therapeutic medications.

Protective effect of ligustrazine on accelerated anti-glomerular basement membrane antibody nephritis in rats is based on its antioxidant properties

Ligustrazine has a renoprotective effect against nephritis. In this study, we further characterized the renoprotective properties of ligustrazine in an experimental model using accelerated anti-glomerular basement membrane antibody (AGBM-Ab). Ligustrazine was given i.p. once daily at 50, 100 mg/kg for 15 days after singly giving i.v. of rabbit anti-rat glomerular basement membrane serum, and showed dose-dependent inhibition the elevation of urinary protein, serum creatinine and blood urea nitrogen as well as the development of glomerular histological changes. Ligustrazine (50 mg/kg) had no affect on glutathione (GSH) content, glutathione peroxidase and catalase activities, but decreased the malondialdehyde (MDA) content and increased superoxide dismutase (SOD) activity in nephritis induced by AGBM-Ab. Ligustrazine (100 mg/kg) significantly decreased MDA content while significantly increased GSH content and SOD, glutathione peroxidase, catalase activities of kidney tissues in the rats treated with AGBM-Ab alone. In conclusion, our results show that ligustrazine has protective activity against accelerated AGBM-Ab nephritis, and its renoprotective effect may be due to its antioxidant properties and inhibition reactive oxygen species (ROS).

Ligustilide induces vasodilatation via inhibiting voltage dependent calcium channel and receptor-mediated Ca2+ influx and release

The purpose of the present study was to investigate the effect of ligustilide on vasodilatation in rat mesenteric artery and the mechanisms responsible for it. Isometric tension of rat mesenteric artery rings was recorded by a sensitive myograph system in vitro. The results showed that ligustilide at concentrations more than 10 microM relaxed potassium chloride (KCl)-preconstricted rat mesenteric artery in a concentration-dependent manner. The vasodilatation effect of ligustilide was not dependent on endothelium. Ligustilide rightwards shifted concentration-response curves induced by KCl, calcium chloride (CaCl(2)), noradrenaline (NA) or 5-hydroxytryptamine (5-HT) in a non-parallel manner. This suggests that the vasodilatation effects were most likely via voltage-dependent calcium channel (VDCC) and receptor-operated calcium channel (ROCC). Propranolol, glibenclamide, tetraethylammonium and barium chloride did not affect the vasodilation induced by ligustilide, showing that beta-adrenoceptor, ATP sensitive potassium channel, calcium-activated potassium channel and inwardly rectifying potassium channel were not involved in the vasodilatation. Ligustilide concentration-dependently inhibited the vasoconstriction induced by NA or CaCl(2) in Ca(2+)-free medium, indicating that the vasodilatation relates to inhibition of extracellular Ca(2+) influx through VDCC and ROCC, and intracellular Ca(2+) release from Ca(2+) store. Since caffeine-induced contraction was inhibited by ligustilide, inhibition of intracellular Ca(2+) released by ligustilide occurred via the ryanodine receptors. Our results suggest that ligustilide induces vasodilatation in rat mesenteric artery by inhibiting the VDCC and ROCC, and receptor-mediated Ca(2+) influx and release.

Screening and analysis of an antineoplastic compound in Rhizoma Chuanxiong by means of in vitro metabolism and HPLC-MS

A new screening and analysis method that combines in vitro metabolism with high-performance liquid chromatography-mass spectrometry (HPLC-MS) was developed for the screening and analysis of an antineoplastic compound, coniferyl ferulate, which is present in the rhizome of Rhizoma Chuanxiong. Infrared (IR), ultraviolet visible spectroscopy (UV-Vis), nuclear magnetic resonance (NMR) and element analysis were used to identify the molecular structure of coniferyl ferulate. The quantitative analysis of coniferyl ferulate in different extracts of Rhizoma Chuanxiong was carried out, and the metabolism of coniferyl ferulate was investigated by in vitro incubation with rat liver homogenate. The metabolite of coniferyl ferulate, ferulic acid ethyl ester, was identified by HPLC-MS, UV-Vis and IR. In addition, antineoplastic activities of coniferyl ferulate and ferulic acid ethyl ester were detected by the MTT assay. The observed inhibition rate of coniferyl ferulate on the activity of HeLa cells was over 80% at 5.4 ng microl(-1). However, its metabolite, ferulic acid ethyl ester, showed no antineoplastic activity in vitro.

Screening, analysis and in vitro vasodilatation of effective components from Ligusticum Chuanxiong

Effective components, ligustilide and butylidenephthalide, from Ligusticum Chuanxiong (Ligusticum wallichii Franchat, Umbelliferae) were screened and identified by using a cell membrane chromatography (CMC) and a gas chromatography/mass spectrometry (GC/MS). The components showed the effects of inhibiting vasoconstriction in vitro on rat abdominal aorta segments. The screening procedure was performed in a rat artery CMC column (50 mm x 2.0 mm I.D.) with a sodium phosphate buffer (pH 7.4) as mobile phase at 37 degrees C. The identification was accomplished by a DB-5MS 30 m capillary column (0.25 mm I.D., 0.25 microm film thickness) with helium as carrier gas operating under program control temperature and electron impact ionization mass spectrometer in a scan mode. Results demonstrated that ligustilide and butylidenephthalide can act on rat artery cell membrane similar to verapamil in CMC system. They significantly inhibited the vasoconstrictions induced by norepinephrine bitartrate (NE) and calcium chloride (CaCl2). The relaxing effect of ligustilide on the NE- and CaCl2-induced constrictions is more potent than that of butylidenephthalide. Ligustilide and butylidenephthalide seem to be the two main effective components of Ligusticum Chuanxiong as a traditional Chinese medicine for treating blood vessel diseases.

A NOVEL IN VITRO ENDOTHELIUM-DEPENDENT VASCULAR RELAXANT EFFECT OF APOCYNUM VENETUM LEAF EXTRACT

1. In the present study, a novel in vitro vascular relaxant effect of Apocynum venetum leaf extract (AVLE; also called 'Luobuma'), obtained from a traditional Chinese medicinal herb with known antihypertensive effects, is reported in isometric contraction studies of rat aorta and superior mesenteric artery. At low concentrations (0.3-10 microg/mL), AVLE had no effect on the resting tension of either blood vessel and caused relaxation in agonist-precontracted vessels with functionally intact endothelium. 2. We demonstrated pharmacologically that the AVLE-induced vasorelaxation was mediated selectively by the endothelial cells in both blood vessels. Using NG-nitro-L-arginine methyl ester (L-NAME) and a low concentration of KCl (15 mmol/L), we also demonstrated that AVLE acted by releasing endothelium-derived relaxation factors; nitric oxide (NO) in the rat aorta and NO plus endothelium-derived hyperpolarizing factor in the rat mesenteric artery. 3. The vascular relaxation following brief exposure to AVLE appeared to persist even after subsequent prolonged washout; this was manifested as an attenuated contraction to subsequent application of phenylephrine (PE) compared with the PE-induced contraction after exposure to carbachol (CCh) and subsequent similar washout. The addition of L-NAME at this point in the absence of AVLE totally restored the contraction to PE, suggesting that enzymatic generation of endothelial NO persisted even after brief exposure to AVLE. 4. Unlike the endothelium-dependent NO-mediated relaxation induced by CCh, which is mediated by endothelial muscarinic receptors (and inhibited by atropine), the relaxation induced by AVLE was not inhibited by atropine and, thus, was not mediated by muscarinic receptors. However, similar to CCh-induced relaxation, AVLE-induced relaxation was associated with the activation of K+ channels. 5. These results provide a strong scientific basis for the folk use of AVLE decoction for antihypertensive therapy in traditional Chinese medicine.

Role of cGMP signals in tetramethylpyrazine induced relaxation of the isolated rat aortic strip

In the present study, role of guanosine-3',5'-cyclic monophosphate (cGMP) in the vasodilatation of tetramethylpyrazine (TMP), one of the active ingredients of the Chinese herb Chuang-xion, was investigated. We found that the TMP could decrease the vascular tone of isolated rat aorta precontracted with phenylephrine (10(-8) M) in a concentration-dependent manner from 10(-5) M to 10(-3) M. Also, the TMP-induced relaxation was reduced by 1H-(1,2,4)-oxadiazol-(4,3-a)-quinoxalin-1-one (ODQ) or methylene blue, the inhibitor of soluble guanylyl cyclase. Moreover, the vasodilative response to TMP was enhanced significantly in the presence of sildenafil, a well-known inhibitor of phosphodiestrase type 5 that is sensitive to cGMP. In addition, TMP could increase the cGMP level in the isolated aortic rings and TMP-induced vasodilatation was deleted by cGMP-dependent protein kinases (PKG) blockade. These results suggest that relaxation of rat aortic strip by TMP is induced in the cGMP-dependent manner.

Chemical Profiles of Methylpyrazines Contained in Commercially Available Natto

Structures and amounts of methylpyrazines contained in commercial natto, a fermented soybean food in Japan, were determined using HPLC equipped with an acid-resistant reversed phase column, Capcell Pak C18 ACR (Shiseido). Mobile phase solvent mixtures consisted of acidic phosphate buffer solution (pH 2.0) containing 2% acetonitrile gave satisfactory results with baseline separation of the authentic specimens, such as naked pyrazine, monomethylpyrazine, 2,3-, 2,5-, and 2,6-dimethylpyrazine, trimethylpyrazine, and tetramethylpyrazine. We used the mobile-phase solvent with a flow rate of 1 ml/min at 15.0 degrees C. Before HPLC, commercial natto samples were treated with water to prepare diluted suspensions of surface mucous materials. The suspensions were treated on Sep-Pac C18 Cartridges (Waters) with phosphate buffer solutions containing 2-7% acetonitrile. The extracts were then injected into the analytical column to obtain chromatograms that were used to determine the structures and amounts of methylpyrazines. The results showed that a commercialiy packed natto contains a considerable amount of 2,5-dimethylpyrazine instead of the tetrametyl- and trimethylpyrazines in the traditional products. This may be a result of recent efforts of natto makers whose interests have been focused on new methods for preparing odorless products.

Effect of tetramethylpyrazine on potassium channels to lower calcium concentration in cultured aortic smooth muscle cells

1. Tetramethylpyrazine (TMP) is one of the active principles contained in Ligusticum chuanxiong Hort. (Umbelliferae), a herb that has been used widely in China to treat vascular disorders. 2. In an attempt to elucidate the possible mechanisms of action of TMP, the effect of TMP on intracellular calcium concentrations ([Ca2+]i) was investigated in cultured vascular smooth muscle (A7r5) cells using the Ca(2+)-sensitive dye Fura-2 as an indicator. 3. The increase in [Ca2+]i in A7r5 cells produced by vasopressin (1 micromol/L) or phenylephrine (1 micromol/L) was attenuated by TMP in a concentration-dependent manner. Only inhibitors specific to ATP-sensitive potassium (KATP) channels or small conductance calcium-activated potassium (SKCa) channels attenuated the action of TMP (10 micromol/L) on [Ca2+]i. However, blockers of other K+ channels failed to modify the inhibitory action of TMP (10 micromol/L) on [Ca2+]i. 4. The action of TMP on membrane potential in A7r5 cells was monitored by the fluorescence of bisoxonol. Tetramethylpyrazine caused a concentration-dependent inhibition of changes in membrane potential elicited by KCl (20 mmol/L) or phenylephrine (1 micro mol/L), an effect that was totally reversed by glibenclamide (100 micromol/L) and apamin (100 nmol/L) in combination. 5. The results obtained indicate that the decrease in [Ca2+]i in A7r5 cells produced by TMP is mediated mainly by opening of KATP and/or SKCa channels.

Mechanisms responsible for the in vitro relaxation of ligustrazine on porcine left anterior descending coronary artery

In this study, we have evaluated the underlying mechanisms responsible for the relaxation response of ligustrazine (2,3,5,6-tetra-methyl-pyrazine; 2,3,5,6-MP) and its structural analogues (2-methyl-pyrazine (2-MP); ethyl-pyrazine (EP); 2,3-di-methyl-pyrazine (2,3-MP); 2,5-di-methyl-pyrazine (2,5-MP); 2,6-di-methyl-pyrazine (2,6-MP) and 2,3,5-tri-methyl-pyrazine (2,3,5-MP)) in porcine left anterior descending coronary artery (tertiary branch, O.D. </=1 mm). In 5-hydroxytryptamine (3 microM) precontracted preparations, cumulative administration (0.1-300 microM) of all pyrazine analogues caused an endothelium-independent, concentration-dependent relaxation. The relative inhibitory potency, as compared at concentration with which 50% relaxation occurred, was 2,3,5,6-MP>2,3,5-MP>EP>2,5-MP>/=2,6-MP>/=2,3-MP>2-MP. Besides, salbutamol and forskolin caused an endothelium-independent relaxation. The relaxation response of ligustrazine, salbutamol and forskolin was blunted in the presence of cis-N-(2-phenylcyclopentyl) azacyclotridec-1-en-2-amine (MDL 12330A) (10 microM, an adenylate cyclase inhibitor) and N-[2-((bromocinnamyl)amino)ethyl]-5-isoquinoline-sulphonamide (H-89, a protein kinase A inhibitor, 3 microM). Patch-clamp, whole-cell electrophysiological studies using single smooth muscle cells of the left anterior descending coronary artery revealed that ligustrazine (300 microM), salbutamol (30 microM) and forskolin (1 microM) inhibited the nifedipine-sensitive L-type Ca(2+) channels, and the inhibitory effect was eradicated by MDL 12330A (10 microM) and H-89 (1 microM). However, neither the Ca(2+)-dependent K(+) channel nor the ATP-dependent K(+) channel was modified by ligustrazine (300 microM). In conclusion, our results indicate that ligustrazine-mediated left anterior descending coronary artery relaxation is due to the activation of adenylate cyclase/protein kinase A cascade and the subsequent inhibition of nifedipine-sensitive, voltage-dependent L-type Ca(2+) channels. However, opening of K(+) channels seems to play no role in mediating the relaxation effect of ligustrazine.