PLANT-DERIVED DRUGS ACTING ON CELLULAR CA2+ MOBILIZATION IN VASCULAR SMOOTH-MUSCLE - TETRAMETHYLPYRAZINE AND TETRANDRINE

The pharmacological profiles of the active ingredients extracted and purified from two well-known Chinese traditional medicinal plants were reviewed. These herbal drugs include tetramethylpyrazine (TMP) and tetrandrine (TET); both have been clinically used in China for the treatment of cardiovascular diseases due to their vasodilatory actions. Studies from this laboratory have confirmed previously reported characteristics of TMP as a Ca2+ antagonist in vascular tissues. However, it also elicited inhibitory effects in response to a wide variety of receptor stimulations as indicated by functional studies and radioligand binding studies using isolated subcellular membranes. TET also inhibited the vascular contraction in response to depolarization by KCI and phenylephrine. It has been found to interact directly with the L-type Ca2+ channel and alpha-adrenoceptor subtypes. Recently, its action on T-type Ca2+ channels has also been demonstrated. These findings collectively suggest that studies of the vasodilatory and antihypertensive effects of these plant-derived drugs on the regulation of cytosolic Ca2+ in vascular smooth muscle are consistent with the current hypothesis of Ca2+ dysfunction as an important etiological factor for the pathogenesis of hypertension.