Abstract
Although the fruit of Nandina domestica THUNBERG (ND) has been used to treat respiratory disorders such as coughing and breathing difficulty in Japan for many years, very little is known about mechanisms underlying its action. In the present study, we investigated effects of the crude extract from ND (NDE) and one of its constituents, nantenine, on contractile responses in isolated guinea pig tracheal ring preparations. In normal experimental condition, guinea pig trachea remained tonically contracted during the resting state, and addition of NDE (1 mg/ml) caused a relaxation of tracheal smooth muscles, but had little effect on the responsiveness of trachea to acetylcholine. The basal, tonic contraction was abolished by the presence of atropine and indomethacin. In this condition, NDE at 0.1-1 mg/ml inhibited histamine-induced contraction in both competitive and non-competitive manners. NDE at 0.01-1 mg/ml inhibited serotonin-induced contraction in a competitive manner. Nantenine (2-20 microM) did not affect histamine-induced contraction, and slightly inhibited serotonin-induced contraction. These results suggest that NDE has inhibitory effects on tracheal smooth muscle contraction, and nantenine cannot account solely for this effect of NDE.
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