Abstract
Objectives : We have examined the relaxational response to the water extract of Rheum palmatum L. in isolated thoracic aorta from sprague dawley (SD) rat in the presence and absence of endothelium. Methods : Rat thoracic aorta was investigated in vessel segments suspended for isometric tension recording by polygraph. Responses to Rhizoma Rhei were investigated in vessels precontracted with 5-hydroxytryptamine. We found that the thoracic aorta segments responded to the water extract of Rheum palmatum L. (ERP) with a dose-dependent vasorelaxation. Results : We found that 1. The thoracic aorta segments responded to ERP with a dose-dependent vasodilation. 2. The 5-HT induced contraction at 10^-4M were inhibited by 85.8% after addition of the 0.1 g/mL water extract of ERP. 3. The 5-HT induced contraction at 10^-4M with and without endothelium were inhibited by 86.4% and 85.8% after addition of the 0.1g/mL ERP. 4. After pre-treatment of the thoracic aorta with 10^-4M N^G-monomethyl-L-arginine (L-NMMA), inducible nitric oxide synthase inhibitor, the vessels has not response to the contraction. Conclusion : In conclusion, ERP induced relaxation in the isolated rat thoracic aorta were composed of dose-dependent relaxation and it has potent vasodilation.