Cajaninstilbene acid (CSA) is a major active component present in the leaves of Cajanus cajan (L.) Millsp. The present study explores the underlying cellular mechanisms for CSA-induced relaxation in rat renal arteries. Vascular reactivity was examined in arterial rings that were suspended in a Multi Myograph System and the expression of signaling proteins was assessed by Western blotting method. CSA (0.1–10 µM) produced relaxations in rings pre-contracted by phenylephrine, serotonin, 9, 11-dideoxy-9α, 11α-epoxymethanoprostaglandin F2α (U46619), and 60 mM KCl. CSA-induced relaxations did not show difference between genders and were unaffected by endothelium denudation, nor by treatment with NG-nitro-L-arginine methyl ester, indomethacin, ICI-182780, tetraethylammonium ion, BaCl2, glibenclamide, 4-aminopyridine or propranolol. CSA reduced contraction induced by CaCl2 (0.01–5 mM) in Ca2+-free 60 mM KCl solution and by 30 nM (−)-Bay K8644 in 15 mM KCl solution. CSA inhibited 60 mM KCl-induced Ca2+ influx in smooth muscle of renal arteries. In addition, CSA inhibited contraction evoked by phorbol 12-myristate 13-acetate (PMA, protein kinase C agonist) in Ca2+-free Krebs solution. Moreover, CSA reduced the U46619- and PMA-induced phosphorylation of myosin light chain (MLC) at Ser19 and myosin phosphatase target subunit 1 (MYPT1) at Thr853 which was associated with vasoconstriction. CSA also lowered the phosphorylation of protein kinase C (PKCδ) at Thr505. In summary, the present results suggest that CSA relaxes renal arteries in vitro via multiple cellular mechanisms involving partial inhibition of calcium entry via nifedipine-sensitive calcium channels, protein kinase C and Rho kinase.

Anemoside A(3), a lupane-type triterpenoid saponin, exists in the roots of Pulsatilla chinensis, but its pharmacological properties are largely unknown. The present study aimed to investigate the mechanisms underlying anemoside A(3)-induced relaxation in rat renal arteries. Changes of isometric force were determined on arteries with a myograph. Anemoside A(3) caused concentration-dependent relaxation in precontracted aortas, mesenteric, left coronary, and renal arteries. Removal of endothelium or treatment with charybdotoxin plus apamin slightly but significantly attenuated the relaxation in renal arteries. TEA(+) inhibited the relaxation caused by anemoside A(3) in renal arteries with and without endothelium while glibenclamide, BaCl(2), or capsaicin had no effect on it. Anemoside A(3) produced less relaxation in rings contracted by 60 mM KCl compared with rings contracted by receptor-dependent constrictors. It further inhibited contractions induced by Ca(2+) influx through nifedipine-sensitive voltage-gated Ca(2+) channels, nifedipine-insensitive receptor-operated Ca(2+) channels, and by intracellular Ca(2+) release. Pretreatment with nifedipine attenuated anemoside A(3)-induced relaxation. Taken together, the present results indicate that anemoside A(3) produces relaxation in rat renal arteries through multiple mechanisms. The release of CTX/apamin-sensitive endothelium-derived hyperpolarizing factor, stimulation of TEA(+)-sensitive K(+) channel, and inhibition of Ca(2+) influx jointly contribute to the relaxation.