INTRODUCTION: The present study was designed to examine whether methylene chloride (CH2Cl2) fraction extracted from Rubus coreanum affects the contractility of the isolated thoracic aortic strips and blood pressure of normotensive rats. METHODS: One of the common carotid arteries or of the femoral arteries was catheterized with a polyethylene tubing. The tubing was connected to a pressure transducer, and pulse of the mean arterial blood pressure was recorded on a biological polygraph continuously. RESULTS: The CH2Cl2 fraction (range, 200 to 800 microg/mL) significantly depressed both phenylephrine (PE, 10 microM)- and high K+ (56 mM)-induced contractile responses of the isolated thoracic aortic strips in a concentration-dependent fashion. In the simultaneous presence of N(omega)-nitro-L-arginine methyl ester hydrochloride (L-NAME) (an inhibitor of nitric oxide [NO] synthase, 300 microM) and the CH2Cl2 fraction (400 microg/mL), both PE- and high K+-induced contractile responses were recovered to the significant level of the corresponding control response in comparison with inhibition of CH2Cl2 fraction treatment alone. Moreover, in the simultaneous presence of the CH2Cl2 fraction after pretreatment with 0.4% CHAPS (3-[(3-cholamidopropyl) dimethylammonio]-1-propane sulfonate), both PE- and high K+-induced contractile responses were recovered to the significant level of the corresponding control response compared to the inhibitory response of CH2Cl2 fraction treatment alone. Also, in anesthetized rats, the CH2Cl2 fraction (range, 0.3 to 3.0 mg/kg) injected into a femoral vein dose-dependently produced depressor responses. This hypotensive action of the CH2Cl2 fraction was greatly inhibited after treatment with phentolamine (1 mg/kg), chlorisondamine (1 mg/kg), L-NAME (3 mg/kg/30 min), or sodium nitroprusside (30 microg/kg/30 min). Intravenous infusion of the CH2Cl2 fraction (range, 1.0 to 10.0 mg/kg/30 min) markedly inhibited norepinephrine-induced pressor responses. DISCUSSION: Taken together, these results demonstrate that the CH2Cl2 fraction causes vascular relaxation in the isolated rat thoracic aortic strips as well as hypotensive action in anesthetized rats. These vasorelaxation and hypotension of the CH2Cl2 fraction seem to be mediated at least by the increased NO production through the activation of NO synthase of the vascular endothelium and the inhibitory adrenergic modulation.