Ligustrazine is a vasodilator of human pulmonary and bronchial arteries

We have investigated the dilator effect of ligustrazine, the semisynthetic principle of a traditional Chinese herbal remedy, on human pulmonary and bronchial arteries in vitro. Ligustrazine caused a concentration-dependent relaxation of human small pulmonary arteries, which was independent of endothelium. Although ligustrazine was equally potent in inducing dilatation of pulmonary and bronchial arteries, it was about 10 times more potent in relaxing small pulmonary arteries (300-500 microns i.d.) compared with lobar pulmonary arteries (7-8 mm i.d.). By contrast, the relaxant responses of small and lobar pulmonary arteries to sodium nitroprusside was not significantly different. Ligustrazine was equally potent in relaxing prostaglandin F2 alpha- or 5-hydroxytryptamine-precontracted pulmonary arteries, suggesting that it is not a prostaglandin F2 alpha or 5-hydroxytryptamine antagonist. Preincubating the vessels with propranolol (1 microM) or indomethacin (10 microM) had no significant effect on the ligustrazine-induced vasodilatation. However, ligustrazine caused concentration-dependent inhibition of calcium-evoked contraction when applied to rat aorta in calcium-free K(+)-depolarizing medium. We conclude that ligustrazine is a dilator of human pulmonary and bronchial arteries, which is endothelium-independent and that ligustrazine preferentially relaxes pulmonary resistance vessels rather than large conduit pulmonary arteries.