Ethanol induces vascular relaxation via redox-sensitive and nitric oxide-dependent pathways

We investigated the role of reactive oxygen species (ROS) and nitric oxide (NO) in ethanol-induced relaxation. Vascular reactivity experiments showed that ethanol (0.03-200 mmol/L) induced relaxation in endothelium-intact and denuded rat aortic rings isolated from male Wistar rats. Pre-incubation of intact or denuded rings with l-NAME (non selective NOS inhibitor, 100 μmol/L), 7-nitroindazole (selective nNOS inhibitor, 100 μmol/L), ODQ (selective inhibitor of guanylyl cyclase enzyme, 1 μmol/L), glibenclamide (selective blocker of ATP-sensitive K(+) channels, 3 μmol/L) and 4-aminopyridine (selective blocker of voltage-dependent K(+) channels, 4-AP, 1 mmol/L) reduced ethanol-induced relaxation. Similarly, tiron (superoxide anion (O(2)(-)) scavenger, 1 mmol/L) and catalase (hydrogen peroxide (H(2)O(2)) scavenger, 300 U/mL) reduced ethanol-induced relaxation to a similar extent in both endothelium-intact and denuded rings. Finally, prodifen (non-selective cytochrome P450 enzymes inhibitor, 10 μmol/L) and 4-methylpyrazole (selective alcohol dehydrogenase inhibitor, 10 μmol/L) reduced ethanol-induced relaxation. In cultured aortic vascular smooth muscle cells (VSMCs), ethanol stimulated generation of NO, which was significantly inhibited by l-NAME. In endothelial cells, flow cytometry studies showed that ethanol increased cytosolic Ca(2+) concentration ([Ca(2+)]c), O(2)(-) and cytosolic NO concentration ([NO]c). Tiron inhibited ethanol-induced increase in [Ca(2+)]c and [NO]c. The major new finding of this work is that ethanol induces relaxation via redox-sensitive and NO-cGMP-dependent pathways through direct effects on ROS production and NO signaling. These findings identify putative molecular mechanisms whereby ethanol, at pharmacological concentrations, influences vascular reactivity.

Pimaradienoic acid inhibits vascular contraction and induces hypotension in normotensive rats

The present investigation was designed to investigate the effect of the diterpene ent-pimara-8(14),15-dien-19-oic acid (pimaradienoic acid, PA) on smooth muscle extracellular Ca2+ influx. To this end, the effect of PA on phenylephrine- and KCl-induced increases in cytosolic calcium concentration ([Ca2+]c), measured by the variation in the ratio of fluorescence intensities (R340/380 nm) of Fura-2, was analysed. Whether bolus injection of PA could induce hypotensive responses in conscious normotensive rats was also evaluated. PA inhibited the contraction induced by phenylephrine (0.03 or 10 μmol L−1) and KCl (30 or 90 μmol L−1) in endothelium-denuded rat aortic rings in a concentration dependent manner. Pre-treatment with PA (10, 100, 200 μmol L−1) attenuated the contraction induced by CaCl2 (0.5 nmol L−1 or 2.5 μmol L−1) in denuded rat aorta exposed to Ca2+-free medium containing phenylephrine (0.1 μmol L−1) or KCl (30 μmol L−1). Interestingly, the inhibitory effect displayed by PA on CaCl2-induced contraction was more pronounced when KCl was used as the stimulant. Phenylephrine- and KCl-induced increases in [Ca2+]c were inhibited by PA. Similarly, verapamil, a Ca2+-channel blocker, also inhibited the increase in [Ca2+]c induced by either phenylephrine or KCl. Finally, bolus injection of PA (1–15 mg kg−1) produced a dose-dependent decrease in mean arterial pressure in conscious normotensive rats. The results provide the first direct evidence that PA reduces vascular contractility by reducing extracellular Ca2+ influx through smooth muscle cellular membrane, a mechanism that could mediate the hypotensive response induced by this diterpene in normotensive rats.