Vasorelaxant and antihypertensive effects of Tianshu Capsule on rats: An in vitro and in vivo approach

Background: Both Chuanxiong (Ligusticum chuanxiong Hort) and Tianma (Gastrodia elata Blume) have the effects of vasorelaxation and antihypertension. However, the effects of Tianshu Capsule (TSC, composed of Chuanxiong and Tianma in the mass ratio of 4:1) on antihypertensive activity have not been explored. This study aimed to investigate the eff ;ects of TSC on vascular tension and blood pressure in rats and to explore the underlying mechanisms. Methods: The vasorelaxant effect of TSC was explored on thoracic aortic rings (both intact endothelium and denuded) preincubated with phenylephrine (Phe) or potassium chloride (KCL). The mechanism was investigated in the presence of antagonists or blockers on aorta isolated from normotensive rats. The in vivo antihypertensive effect was assessed using a tail-cuff method on spontaneously hypertensive rats (SHRs). Results: TSC (0.125-4 mg/mL) produced a concentration-dependent vasorelaxation on aortic rings preincubated with Phe (1 mu M) or KCL (60 mM). Removal of aorta endothelium markedly attenuated the TSC activity. Pretreatment of aortic rings with beta-adrenoceptor blocker propranolol (1 mu M), muscarinic receptor antagonist atropine (1 mu M), cyclooxygenase inhibitor indomethacin (IDO, 1 mu M), adenylyl cyclase inhibitor 9-(tetrahydro-2-furanyl)-9H-purine-6-amine (SQ22536, 100 mu M), K(+)channel blockers 4-aminopyridine(4-AP, 1 mM) or barium chloride(BaCl2, 1 mM) followed by addition of Phe (1 mu M) prior to TSC did not influence the TSC-induced relaxation. In contrast, the vasorelaxant effects of TSC were markedly inhibited by the NO synthase inhibitor L-NG-nitroarginine methyl ester (L-NAME, 10 mu M), guanylyl cyclase inhibitor 1H- [1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ, 10 mu M), K+ channel blockers, glibenclamide (100 mu M) and clotrimazole (5 mM). Moreover, TSC (2 mg/mL, 4 mg/mL) inhibited CaCl2-induced contractions and caused a concentration-dependent rightward shift of the response curves. Additionally, TSC (2 mg/mL, 4 mg/mL) depressed the constriction caused by Phe (1 mu M) in the absence of extracellular Ca2+. Furthermore, TSC (2.15 g/kg) lowered the systolic blood pressure (SBP), with no alteration in heart rate (HR) in SHRs. Conclusions: These findings demonstrated that TSC induced vasorelaxant effects via both endothelium-dependent and endothelium-independent pathways. The NO/sGC/cGMP pathway, ATP-sensitive K+ channels, Ca2+- activated K+ channels, inhibition of extracellular Ca2+ influx and intracellular Ca2+ release were probably involved in this relaxation. The vasorelaxant effects of TSC may make the greatest contribution to the reduction in high blood pressure.