| Resumo: |
(+)-Rose oxide (OR), β-citronellol (BC) and geraniol (GE) are chemically related monoterpenes found naturally in several essential oils, such as in bulgarian rose and geranium oil. While the pharmacological actions of OR are still scarce, some reports show that BC and GE act potentially as inhibitors of Ca2+ channels in vascular smooth muscle. As chemically related molecules, the objective of this study was to compare the effects of OR, BC and GE on aortic contractility isolated from rats. Isometric records were obtained from aortic rings through a data acquisition system. In aortic rings with intact endothelium, OR, BC and GE (1 - 3000 μM) relaxed the contraction induced by phenylephrine with EC50 values [I.C. 95%] of 1715.9 [1386.6-2123.4], 342.6 [110.2-1065.8] and 930.8 [758.8-1141.7] μM, respectively. Already in KCl induced contraction (60 mM) the OR had EC50 of 550.6 [245.6-1234.4] μM, BC of 98.3 [42.8 - 225.7] μM and GE of 217,5 [156.4-302.5] μM. The vasorelaxant effects of monoterpenes on contractions induced by phenylephrine or KCl were not significantly (P> 0.05, Mann-Whitney) altered by endothelial removal, treatment with L-NAME or tetraethylammonium. The EC50 values of the monoterpenes in phorbol ester pre-contracted preparations (973.6 [389.7-2432.2] μM for OR, 77.8 [14.4-419.2] μM for BC and 151, 2 [46.21 - 494.6] μM for GE) and U46619 (533.6 [212.4-1340.8] μM for OR, 106.7 [53.6 - 212.1] μM for BC and 386,8 [207.1 - 722.4] μM for GE), were significantly lower (p <0.01, Mann-Whitney) than the values obtained in pre-contraction induced by phenylephrine in the aorta. In Ca2+-free medium in the presence of KCl (60 mM), contractions caused by the addition of Ca2+ were significantly reduced by OR, BC and GE (from 600μM), but when phenylephrine was added instead of K+, there was no decrease in the magnitude of the contractile response. The present study suggests that the vasorelaxant activity of these monoterpenes in rat aorta involves inhibition of voltage-operated calcium channels in the following order of pharmacological potency: BC > GE > OR. |
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