The semi-synthetic kaurane ent-16α-methoxykauran-19-oic acid induces vascular relaxation and hypotension in rats

Abstract

The present work investigates the mechanisms involved in the vasorelaxant effect of ent-16α-methoxykauran-19-oic acid (KA–OCH3), a semi-synthetic derivative obtained from the kaurane-type diterpene ent-kaur-16-en-19-oic acid (kaurenoic acid). Vascular reactivity experiments were performed in aortic rings isolated from male Wistar rats using standard muscle bath procedures. The cytosolic calcium concentration ([Ca2+]c) was measured by confocal microscopy using the fluorescent probe Fluo-3 AM. Blood pressure measurements were performed in conscious rats. KA–OCH3 (10, 50 and 100μmol/l) inhibited phenylephrine-induced contraction in either endothelium-intact or endothelium-denuded rat aortic rings. KA–OCH3 also reduced CaCl2-induced contraction in a Ca2+-free solution containing KCl (30mmol/l) or phenylephrine (0.1μmol/l). KA–OCH3 (0.1–300μmol/l) concentration-dependently relaxed endothelium-intact and endothelium-denuded aortas pre-contracted with either phenylephrine or KCl, to a greater extent than kaurenoic acid. Moreover, a Ca2+ mobilisation study showed that KA–OCH3 (100μmol/l) inhibited the increase in Ca2+ concentration in smooth muscle and endothelial cells induced by phenylephrine or KCl. Pre-incubation of intact or denuded aortic rings with NG-nitro-l-arginine methyl ester (L-NAME, 100μmol/l), 7-nitroindazole (100μmol/l), wortmannin (0.5μmol/l) and 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 1μmol/l) produced a rightward displacement of the KA–OCH3 concentration–response curve. Intravenous administration of KA–OCH3 (1–10mg/kg) reduced mean arterial blood pressure in normotensive rats. Collectively, our results show that KA–OCH3 induces vascular relaxation and hypotension. The mechanisms underlying the cardiovascular actions of KA–OCH3 involve blockade of Ca2+ influx and activation of the NO-cGMP pathway.