THE RELATION OF ENDOGENOUS CATECHOLAMINE TO THE ACTION OF STROPHANTHIN-G ON ATRIAL CONTRACTIONS OF RABBITS AND GUINEA-PIGS

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Abstract
The positive inotropic and toxic effects of strophanthin-G were studied on atrial preparations from rabbits and guinea-pigs. Strophanthin-G augmented the action of available endogenous catecholamine released by nicotine, and the positive inotropic effect of strophanthin-G was strengthened by L-methionine which may accelerate the metabolism of endogenous catecholamine. The positive inotropic effect of strophanthin-G on atria was not syner-gistic with exogenous adrenaline. The rabbit atria arrested by reserpine 3 x 10-5 were resumed by the application of strophanthin-G after the reserpine had been washed out, while the same resumption did not occur with atria excised from animals pretreated with reserpine 1 mg/kg 24 hours before the experiment. The atria, in which the endogenous catecholamine may have been extremely decreased by the pretreatment with larger doses of reserpine, did not respond to strophar.thin-G but could respond to the same drug in the presence of endo- as well as exogenous catecholamine. In such cases of extremelyexhaustedendog-enous catecholamine content, however, the toxic effect of strophanthin-G was remarkably decreased. The toxic effects of strophanthin-G on normal atria were scarcely different from those on atria which were excised from rabbits or guinea-pigs pretreated with reserpine 1 mg/kg 24 hours before experiment, though they were potentiated by excessive exogenous catecholamine.