Cardiotonic flavonoids from Citrus plants (Rutaceae).

Two flavonoids, 3,5,6,7,8,3',4'-heptamethoxyflavone (HEPTA) and natsudaidain isolated from Citrus plants (Rutaceae), produced a positive inotropic effect (PIE) on guinea-pig papillary muscle. Natsudaidain (pD2 4.98 +/- 0.07) was more potent than HEPTA (pD2 4.33 +/- 0.08), but the maximum PIE of HEPTA was greater than that of natsudaidain. The PIE of HEPTA was completely inhibited by reserpinization of the guinea pig, and partially inhibited by metoprolol and carbachol. The carbachol inhibition was omitted by atropine. The mechanism of PIE of HEPTA is accounted for catecholamine release from cardiac tissue.