Investigation of Mechanisms Involved in (-)-Borneol-Induced Vasorelaxant Response on Rat Thoracic Aorta

The monoterpene (-)-borneol is present in essential oils of several medicinal plants. The aim of this study was to evaluate (-)-borneol effects on rat thoracic aorta artery rings. The cumulative addition of (-)-borneol (10(-9)-3 x 10(-4) M) on a phenylephrine-induced pre-contraction (10(-6) M) promoted a vasorelaxant effect in a concentration-dependent manner and independent of vascular endothelium. A similar effect was obtained on KCl-induced pre-contractions (80 mM). (-)-Borneol (10(-5)-3 x 10(-4) M) inhibited contractions induced by cumulative addition of CaCl2 (10(-6)-3 x 10(-2) M) in depolarizing medium without Ca2+ in a concentration-dependent manner. On S-(-) Bay K 8644-induced pre-contractions (10(-7) M), (-)-borneol did not induce significant changes compared with KCl-induced pre-contractions. In a Ca2+-free medium, (-)-borneol (10(-5), 10(-4) or 10(-3) M) interfered in calcium mobilization from phenylephrine (10(-6) M)-or caffeine (20 mM)-sensitive intracellular stores. The involvement of K+ channels was evaluated by tetraethylammonium (3 mM), 4-aminopyridine (1 mM) and glibenclamide (10(-5) M) pre-treatment, and (-)-borneol-induced vasorelaxation was markedly attenuated. Thus, this vasorelaxant effect can probably be attributed to calcium influx blockade through voltage-operated calcium channels (CavL), calcium mobilization from intracellular stores and potassium channels activation.