Correlation of antioxidative properties and vaso-relaxation effects of major active constituents of traditional Chinese medicines

Scutellaria baicalensis Georgi (Labiatae) ("huang qin"), Ligusticum chuanxiong Hort. (Umbelliferae) ("chuang xiong"), Panax notoginseng (Burk.) F.H. Chen (Araliaceae) ("san qi"), Uncaria rhynchophylla (Miq.) Jackson. (Rubiaceae) ("gou teng"), Rhokiola rosea L. (Crassulaceae) ("hong jing tian") and Stephania tetrandra S. Moore (Menispermaceae) ("fang ji") are commonly used traditional Chinese medicine (TCM) for hypertensive patients. The pharmacologically active compounds found in these TCMs are baicalin, ligustrazine, notoginsenoside R1, rhynchophylline, salidroside and tetrandrine, respectively, which possess antihypertensive properties with diverse cellular mechanisms. In this study, we attempted to evaluate a possible correlation of the antioxidative activities (using the DPPH assay) and the vaso-relaxation effects (using rat isolated thoracic aorta) of these compounds. In the antioxidative study, a relative order of free radical scavenging capacity (SR%) of baicalin ≥ tetradrine >> salidroside ≥ ligustrazine ≥ rhynchophylline ≈ notoginsenoside R1 was demonstrated. In the vaso-relaxing study, a relative order of the maximum relaxation response (at 3mM) of tetradrine > baicalin ≫ ligustrazine > notoginsenoside R1 ≈ rhynchophylline > salidroside was recorded. A positive correlation (R²=0.7741) between the antioxidative activity and the vascular relaxation effect of the compounds evaluated was illustrated. In contrast, ascorbic acid only elicited a free radical scavenging activity with no apparent relaxation effect, whereas nifedipine (a Ca²⁺ channel blocker) caused a marked vascular relaxation with no obvious free radical scavenging activity. Hence, our results suggest, for the first time, that the therapeutic effect (e.g., antihypertensive) of these TCM-oriented drugs, unlike western medicine, are probably correlated with the unique antioxidative potential of these compounds.