Inhibition of Vasoconstriction by Tetramethylpyrazine

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Abstract
Using dog mesenteric arterial ring preparations, we studied the in vitro vascular effects of tetraethylpyrazine (TMP, also known as Ligustrazine), a vaoactive component derived from Ligustium Wollichii ranchat; a widely used ingredient in Chinese herbal edicine for the treatment of cardiovascular diseases. MP had no effect on the resting force of the vascular uscle, but it caused a dose-dependent inhibition of vasular contractile responses to KCl and phenylephrine PHE). These inhibitory effects of TMP were reversible and more prominent at lower agonist concentrations. TMP also inhibited the responses to PHE in Ca-free medium containing 50 μM EGTA suggesting the action on the release of intracellular Ca2+. Therefore, TMP is not a specific Ca-channel blocker as claimed previously. Its vasodilatory effect is mediated by the inhibition of Ca influx, as well as the release of intracellular Ca2+.

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