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.

TRPM8 Channel Activation Induced by Monoterpenoid Rotundifolone Underlies Mesenteric Artery Relaxation.

In this study, our aims were to investigate transient receptor potential melastatin-8 channels (TRPM8) involvement in rotundifolone induced relaxation in the mesenteric artery and to increase the understanding of the role of these thermosensitive TRP channels in vascular tissue. Thus, message and protein levels of TRPM8 were measured by semi-quantitative PCR and western blotting in superior mesenteric arteries from 12 week-old Spague-Dawley (SD) rats. Isometric tension recordings evaluated the relaxant response in mesenteric rings were also performed. Additionally, the intracellular Ca2+ changes in mesenteric artery myocytes were measured using confocal microscopy. Using PCR and western blotting, both TRPM8 channel mRNA and protein expression was measured in SD rat mesenteric artery. Rotundifolone and menthol induced relaxation in the isolated superior mesenteric artery from SD rats and improved the relaxant response induced by cool temperatures. Also, this monoterpene induced an increase in transient intracellular Ca2+. These responses were significantly attenuated by pretreatment with capsazepine or BCTC, both TRPM8 channels blockers. The response induced by rotundifolone was not significantly attenuated by ruthenium red, a non-selective TRP channels blocker, or following capsaicin-mediated desensitization of TRPV1. Our findings suggest that rotundifolone induces relaxation by activating TRPM8 channels in rat superior mesenteric artery, more selectively than menthol, the classic TRPM8 agonist, and TRPM8 channels participates in vasodilatory pathways in isolated rat mesenteric arteries.

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.