Kavain attenuates vascular contractility through inhibition of calcium channels

Kavain is a biologically active compound from the Oceanic plant Piper methysticum (kava). Traditional medicinal uses of the kava root are many. Kava is increasingly being utilized by Western societies for its anxiolytic effects. Recent reports indicate that kavain blocks ion channels in neural tissue, relaxes precontracted ileum, and relaxes precontracted airway. Thus, we investigated the potential ability of this plant-derived compound to alter vascular smooth muscle function. Thoracic aortae were isolated from Sprague-Dawley rat and cut into 4 mm rings. Rings were placed in tissue baths and suspended from force-displacement transducers for the measurement of isometric tension. In a dose-dependent manner, kavain (10(-6) M to 10(-3) M) was found to relax aortic rings precontracted with phenylephrine (PE). This response was not dependent on functional endothelium. In addition, kavain pretreatment (3 x 10(-5) M or 3 x 10(-4) M) attenuated vascular smooth muscle contraction evoked by PE. However, kavain failed to attenuate PE-mediated contraction in calcium (Ca(++))-free buffer, indicating that intracellular signaling processes were likely not affected. Also, kavain did attenuate the contraction elicited by administration of Ca(++) to depolarized tissue. Interestingly, in rings pre-treated with the selective L-type Ca(++) channel blocker nifedipine, kavain-mediated relaxation was inhibited. Lastly, in rings selectively contracted with an L-type calcium channel activator, kavain elicited dose-dependent (and ultimately complete) relaxation. These data strongly suggest that kavain impairs vascular smooth muscle contraction, likely through inhibition of Ca(++) channels.