Calcium influx inhibition is involved in the hypotensive and vasorelaxant effects induced by yangambin.

The pharmacological effects on the cardiovascular system of yangambin, a lignan isolated from Ocotea duckei Vattimo (Lauraceae), were studied in rats using combined functional and biochemical approaches. In non-anaesthetized rats, yangambin (1, 5, 10, 20, 30 mg/kg, i.v.) induced hypotension (-3.5 ± 0.2; -7.1 ± 0.8; -8.9 ± 1.3; -14 ± 2.3, -25.5% ± 2.6%, respectively) accompanied by tachycardia (5.9 ± 0.5; 5.9 ± 1.6; 8.8 ± 1.4; 11.6, 18.8% ± 3.4%, respectively). In isolated rat atria, yangambin (0.1 µM-1 mM) had very slight negative inotropic (Emax = 35.6% ± 6.4%) and chronotropic effects (Emax = 10.2% ± 2.9%). In endothelium-intact rat mesenteric artery, yangambin (0.1 µM-1 mM) induced concentration-dependent relaxation (pD2 = 4.5 ± 0.06) of contractions induced by phenylephrine and this effect was not affected by removal of the endothelium. Interestingly, like nifedipine, the relaxant effect induced by yangambin was more potent on the contractile response induced by KCl 80 mM (pD2 = 4.8 ± 0.05) when compared to that induced by phenylephrine. Furthermore, yangambin inhibited CaCl2-induced contractions in a concentration-dependent manner. This lignan also induced relaxation (pD2 = 4.0 ± 0.04) of isolated arteries pre-contracted with S(-)-Bay K 8644. In fura-2/AM-loaded myocytes of rat mesenteric arteries, yangambin inhibited the Ca2+ signal evoked by KCl 60 mM. In conclusion, these results suggest that the hypotensive effect of yangambin is probably due to a peripheral vasodilatation that involves, at least, the inhibition the Ca2+ influx through voltage-gated Ca2+ channels.

Endothelium-derived nitric oxide contributes to the vasorelaxant response induced by mesoionic 2-(4-chlorophenyl)-3-methyl-4-(4-methoxyphenyl)-1;3-thiazolium-5-thyolate (CMMTT) in rats.

This study was performed to investigate the mechanisms involved in the vasorelaxation induced by mesoionic 2-(4-chlorophenyl)-3-methyl-4-(4-methoxyphenyl)-1;3-thiazolium-5-thyolate (CMMTT), a newly synthesized mesoionic compound, in rat superior mesenteric arteries. In phenylephrine (10 microM)-pre-contracted mesenteric rings, CMMTT (10(-14) - 10(-6) M) induced a concentration-dependent relaxation [pD(2) = 10.26 +/- 0.05, E(max) = 80.8 +/- 5.8%], and this effect was almost abolished after either removal of the vascular endothelium [E(max) = 17.7 +/- 4.2%, P<0.001], removal of the vascular endothelium plus100 microM N(omega)-nitro-L-arginine methyl esther (L-NAME) [E(max) = 21.0 +/- 2.0 %, P<0.001], or after pre-treatment of the rings with 100 microM L-NAME [E(max) = 13.3 +/- 2.4%, P<0.001] or 10 microM 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ) [E(max) = 13.6 +/- 4.8%, P<0.001]. However, endothelium-dependent relaxation induced by CMMTT was not significantly modified after 1 microM indomethacin plus 1 nM atropine [pD(2) = 11.12 +/- 0.08, E(max) = 73.8 +/- 5.15%] or 100 nM charybdotoxin (ChTX) plus 100 nM apamin [pD(2) = 10.89 +/- 0.08, E(max) = 58.91 +/- 9.8%]. In mesenteric rings, CMMTT (10(-6) M) was able to increase nitric oxide (NO)(x) levels, and this effect was abolished after removal of the vascular endothelium. In conclusion, the present study, using combined functional and biochemical approaches, demonstrated that CMMTT induced a significant vasorelaxant effect, almost completely mediated by the endothelium, likely via NO release and activation of the NO-cGMP pathway.

Mechanisms involved in the vasodilator effect induced by diosgenin in rat superior mesenteric artery.

The aim of this study was to investigate the vasorelaxant effect induced by diosgenin in superior mesenteric rings. In rings pre-contracted with phenylephrine (10 microM), diosgenin caused concentration-dependent relaxations [EC(50) = (3.3 +/- 1.2) x 10(- 4)M, E(max) = 94.2 +/- 2.6 %]. Vascular relaxation induced by diosgenin was significantly inhibited after removal of the endothelium (E(max) = 46 +/- 8.8%, p < 0.001) or after pre-treatment of the rings with N-nitro-L-arginine methyl esther (l-NAME) 100 or 300 microM (E(max) = 35.3 +/- 4%; 28.1 +/- 3.3%, respectively, p < 0.001), atropine 1 microM (E(max) = 24.6 +/- 3.4%, p < 0.001), hydroxocobalamin 30 microM (E(max) = 54.0 +/- 9.6%, p < 0.001), 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ) 10 microM (E(max) = 46.0 +/- 8.0%, p < 0.001) or indomethacin 1 microM (E(max) = 22.6 +/- 11.8%, p < 0.001). Vasorelaxation evoked by diosgenin was significantly inhibited after pre-treatment of preparations with both selective and non-selective inhibitors of large conductance Ca(2+)-activated K(+) (BK(Ca)) channels, iberiotoxin 100 nM or tetraethylammonium (TEA) 1mM, respectively (E(max) = 62.5 +/- 9.1%; 65.7 +/- 1.1%, p < 0.001). Conversely, in endothelium-denuded vessels, none of BK(Ca) channel blockers modified the relaxant effect induced by diosgenin. In mesenteric endothelial cells loaded with FURA-2 diosgenin was able to increase intracellular calcium concentrations, which were significantly decreased by atropine 1 microM. In addition, in isolated mesenteric rings, diosgenin induced marked increase in nitric oxide (NO) levels, which was completely abolished after functional endothelium removal. The results obtained here demonstrated that diosgenin-induced relaxation appears to involve endothelial muscarinic receptor activation with increase in intracellular calcium concentrations and consequent release of endothelium-derived relaxing factors (EDRFs), mainly NO and cyclooxygenase derivatives, which activate BK(Ca) channels. Nevertheless, further studies are necessary to clearly elucidate residual endothelium-independent relaxation induced by diosgenin.