We previously detected compounds with vasorelaxant effects, such as methyl brevifolincarboxylate, from the leaves of Phyllanthus niruri, 2) ebricoic acid from the extract of Phellinus givus, 3) and forsythiaside from the fruit of Forsythia suspensa. 4) In our attempts to search for compounds with vasorelaxant effects from various plants, in the present study we isolated three constituents from the heartwood of Acer nikoense (Aceraceae): A. nikoense is a Japanese folk medicine used as a remedy primarily for hepatic disorders. Constituents previously isolated from the bark and leaves are diarylheptanoids, phenolic compounds, and tannin, 5) and their bioactivities such as antiinflammatory effects 6) and protective effects against hepatic injury 7) were also reported. First, we found that the organic extract from the heartwood of A. nikoense showed vasorelaxant effects on rat aorta with or without endothelium. Second, scopoletin (1), cleomiscosin A (2), and aquillochin (3) were isolated as major constituents using SiO 2 chromatography. 8) Moreover, the results of our literature search revealed that 1 had vasorelaxant effects by inhibiting intracellular calcium mobilization from norepinephrine (NE)-sensitive stores.9) Consequently, we focused on the vasorelaxant effects of 2 and 3 isolated from the organic extract of the heartwood of A. nikoense and investigated their effects in comparison with that of 1, which was used as a positive control in the present study. MATERIALS AND METHODSPlant Material Dried A. nikoense heartwood was obtained from the Medicinal Plant Garden of Hoshi University, and identified by one of the authors (S.N.).Chemicals NE, nicardipine, ethyleneglycol-bis-(b-aminoethyl ether)-tetraacetic acid (EGTA), and acetylcholine chloride (Ach) were purchased from Sigma Chemical (St. Louis, MO, U.S.A.). Authentic samples of 1-3 were obtained from one of the authors (S.N.) (Fig. 1).Extraction and Isolation Dried A. nikoense heartwood (62.5 g) was extracted with MeOH, and the extract solution was evaporated in vacuo. The residual extract (5.0 g) was further extracted successively with diethyl ether, ethyl acetate, and water. Then the extracts were evaporated in vacuo to obtain extracts of 0.51 g, 0.82 g, and 2.07 g from the successivesolvents. Among the extracts tested for vasorelaxant effects on rat aorta, the ether extract exhibited the most potent relaxant effects on NE-induced aortic contraction. Compounds 1, 2, and 3 of A. nikoense were found in the diethyl ether fraction. 8)Assay for Vasorelaxation Experimental studies using animals were conducted in accordance with the Guiding Principles for the Care and Use of Laboratory Animals, Hoshi University, and under the supervision of the Committee on Animal Research of Hoshi University, which is accredited by the Ministry of Education, Science, Sports Culture and Technology of Japan. Isolation of Rat Aortic StripsThe preparation of aortic rings and measurement of tension were performed as previously described.2-4) In brief, male Wistar rats weighing 240-340...
Aim: The bark of Acer nikoense (Aceraceae) is used in Japanese folk medicine as a remedy for hepatic disorders and eye diseases. The aim of this study was to investigate the vasorelaxant effects of A. nikoense extracts and further clarify the active constituents and mechanisms of action. Methods: Dried A. nikoense bark was extracted with methanol. The extract was further extracted with diethyl ether, ethyl acetate, and 1-butanol, successively. The major constituents of the extracts were isolated using chromatography. Vasorelaxant effects of the extracts and isolated constituents were assessed using isolated rat aorta. The aorta was placed in a welloxygenated bath of modified Krebs-Henseleit solution and the mechanical tension measured isometrically. Results: The extracts had a vasorelaxant effect on aorta precontracted with 3 × 10 −7 mol/L norepinephrine (NE). Isolated major constituents of A. nikoense bark, diarylheptanoids, such as acerogenin A (compound 1), B (compound 2), (−)-centrolobol (compound 3), aceroside I (compound 5), B1 (compound 6), VII (compound 7) III (compound 8), and phenolic compound, (+)-rhododendrol (compound 4) were examined. Compounds 1 and 3 had vasorelaxant effects on rat aorta with or without endothelium in the NE-induced preparation. Furthermore, compounds 1 and 3 inhibited contraction induced by a high concentration (60 mmol/L) of K + and also had a moderate inhibitory effect on NE-induced vasoconstriction in the presence of nicardipine. Conclusion: The inhibition of NE-induced vasoconstriction by compounds 1 and 3 may be attributed to factors such as endothelial independency by blocking of Ca 2+ influx via voltage-dependent Ca 2+ channels and receptor-operated Ca 2+ channels.
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