POTENTIATION OF BETA-ADRENERGIC FUNCTION BY SAIBOKU-TO AND BAKUMONDO-TO IN CANINE BRONCHIAL SMOOTH-MUSCLE

To determine the effects of the Kampo drugs Saiboku-to, Bakumondo-to a nd Orengedoku-to on beta-adrenergic function in airway smooth muscle, we studied isolated canine bronchial segments under isometric conditio ns in vitro. Incubation of tissues with these drugs did not alter the contractile responses to acetylcholine and histamine. The relaxation o f tissues precontracted with acetylcholine induced by isoproterenol wa s augmented by Saiboku-to and Bakumondo-to, so that the concentration of isoproterenol required to produce a half-maximal effect (IC50) was decreased from 4.6+/-0.5 x 10(-8) M to 1.9+/-1.0 x 10(-8) M (P<0.05) a nd to 1.0+/-0.8 X 10(-8) M (P<0.01), respectively, whereas Orengedoku- to had no effect. These effects were concentration-dependent with the threshold concentrations being 0.3 mg/ml for Saiboku-to and 0.1 mg/ml for Bakumondo-to. Saiboku-to and Bakumondo-to did not affect cyclic AM P levels in airway smooth muscle per se but potentiated the isoprotere nol-induced cyclic AMP accumulation. These results suggest that Saibok u-to and Bakumondo-to but not Orengedoku-to potentiate beta-adrenergic function in airway smooth muscle, which may reflect the efficacy of t hese drugs on airway hyperresponsiveness and asthma.