Abstract
Objectives: We have examined the relaxational response to the water extract of Rheum palmatum L. (ERP), R undulatum L (ERU) and its components in isolated thoracic aorta from sprague dawley (SD) rat. Methods: Rat thoracic aorta was investigated in vessel segments suspended for isometric tension recording by polygraph. Responses to ERP and ERU were investigated in vessels precontracted with 5-hydroxytryptamine. We found that the thoracic aorta segments responded to the water extract of ERP and ERU with a dose-dependent vasorelaxation. Results: We found that 1. The thoracic aorta segments responded to ERP and ERU with a dose-dependent vasodilation. 2. The 5- HT induced contraction at $10^{-4}M$ were inhibited by $85.8\%\;and\;64.4\%$ after addition of the 0.1g/mL water extract of ERP and ERU. 3. The 5-HT induced contraction at $10^{-3}M$ were inhibited by $100\%\;after\;10^{-3)M$ emodin. 4. The amounts of emodin were $3.15\%\;and\;2.26\%$ in Rheum palmatum L. and R. undulatum L, respectable. Conclusion: In conclusion, ERP and ERU induced relaxation in the isolated rat thoracic aorta were composed of dose-dependent relaxation and it's major component, emodin, has potent vasodilation.