[Effects of extract from a herbal drug, cnidium rhizome (senkyu), on contraction, heart rates and membrane potentials of isolated guinea pig atria].

Effects of extract from a herb, Cnidium rhizome (Senkyu), on isolated guinea pig atria were investigated pharmacologically and electrophysiologically. The methanol extract from Cnidium rhizome decreased the contraction and slightly increased the heart rates of the isolated atria. Extracts from five other herbs, such as Japanese anglica root (Toki), Peony root (Shakuyaku), Moutan bark (Botanpi), Glycyrrhiza (Kanzo), Bupleurum (Saiko), affected neither the contraction nor the heart rates. The methanol extract from Cnidium rhizome was fractionated with chloroform and water fractions. The chloroform fraction exerted potent negative inotropic and chronotropic effects in isolated atria. The contraction was attenuated by two major components in the chloroform fraction, ligustilide and senkyunolide, but the heart rates were scarcely affected by these components. The chloroform fraction induced changes in resting potentials and configurations of normal action potentials recorded in the isolated left atria: the resting potentials were depolarized, and the upstroke velocity of the action potentials decreased. Neither ligustilide nor senkyunolide exerted such effects. The upstroke velocity of action potentials recorded in partially depolarized atria was reduced by the chloroform fraction as well as ligustilide and senkyunolide. The mechanisms underlying the effects of the extract from Cnidium rhizome were discussed.