Vascular effects of selected antihypertensive drugs derived from traditional medicinal herbs.
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1. The pharmacological actions of the active ingredients extracted or purified from two selected traditional Chinese medicinal plants on vascular smooth muscles are briefly reviewed. The active ingredients of these herbal drugs include tetrandrine (TET) and total ginseng saponins (TGS). These natural products have been clinically used in China for the treatment of cardiovascular diseases due to their vasodilatory and antihypertensive actions. 2. Studies from this laboratory have confirmed previously reported characteristics of these drugs as Ca2+ antagonists in vascular tissues. On the other hand, they also elicited inhibitory effects in response to a wide variety of receptor stimulations as indicated by contractility studies using isolated vascular tissues and radioligand binding studies using isolated subcellular membranes. 3. TET has been demonstrated as an effective but not very selective Ca2+ antagonist. Other than the vasodilatory action on arteries and veins, TET also shows a vasoconstrictive effect in veins. 4. TGS from panax notoginseng may be acting as a novel and selective Ca2+ antagonist that does not interact with the L-type Ca2+ channel (e.g. in KCl-induced contraction) but may interact with the putative receptor operated Ca2+ channel (e.g. in phenylephrine-induced contraction). TGS from panax quinquefolium, on the other hand, enhanced the vasoconstrictor effect produced by phenylephrine, but not KCl.
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