The candidates responsible for vasorelaxation action of rutin-free tartary buckwheat extract (TBSP) were examined in this study. As a result of reversed-phase high-performance liquid chromatography (HPLC) separations, five prominent peaks in the acidic fraction of TBSP were obtained at 260 nm. Among the five collected peaks, we successfully identified four compounds by nuclear magnetic resonance (NMR) and mass spectrometry (MS) measurements: (+)-osbeckic acid as a dimer ([M - H](-) m/z: 371.2 > 184.9 > 140.9), 5-hydroxymethyl-2-furoic acid, protocatechuic acid, and p-hydroxybenzoic acid. A vascular contractive measurement in 1.0 μM phenylephrine-contracted Sprague-Dawley rat thoracic aorta rings revealed that (+)-osbeckic acid dimer evoked a potent vasorelaxant effect with an EC50 value of 887 μM compared to other isolates (EC50: 5-hydroxymethyl-2-furoic acid, 3610 μM; protocatechuic acid, 2160 μM; p-hydroxybenzoic acid, no inhibition). Dimeric (+)-osbeckic acid was stable in solutions and at high temperatures, while its degraded peak on the HPLC chromatogram was observed when it was dissolved in dimethyl sulfoxide.

Adenine had a concentration-dependent relaxation action on the phenylephrine-contracted aorta ring, with an EC 50 value of 0:40 AE 0:12 mM. This effect was also observed in the endothelium-denuded aorta. Among the adenine analogues, N-methyladenine and benzimidazole still evoked an apparent relaxation effect, while 1-, 3-or 7-methyladenine and imidazole were no longer vasodilators. These findings demonstrate that the imino group from the uncharged imidazolium moiety in adenine played a key role in the relaxation of the contracted aorta.

Fourteen standard rice varieties with high temperature tolerance at the ripening stage in Kyushu region were selected based on apparent by an evaluation of grain quality after ripening under high temperature condition at eight breeding stations,

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