The Relation of Endogenous Catecholamine to the Actions of Strophanthin-G on Rabbits and Guinea-pigs
1964 Volume 16 Issue 1 Pages 58-67
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1964 Volume 16 Issue 1 Pages 58-67
The actions of therapeutic and toxic doses of strophanthin-G on the rhythmiccontractions of isolated atria were examined on rabbits and guinea-pigs.
The atrial contractions of rabbits were arrested when reserpine 3×10-5g/ml was. added to the bath. These arrested atria did not resume spontaneously, even when the bathfluid was repeatedly changed. But a small concentration of strophanthin-G 10-6g/ml caused the resumption of atrial movement. When rabbit atria excised from animals pretreated with reserpine 1 mg/kg subcutaneosly injected were arrested byreserpine 3×10-5g/ml, the beating caused by strophanthin-G was not seen after large concentration 2×10-6g/ml was applied to the bath.
A small concentration of strophanthin-G 10-6g/ml caused a gradual increase of the amplitude of atrial movement of guinea-pigs. But a large concentration of strophanthin-G 1.5×10-6 to 1.75×10-6g/ml caused atrial arrest after a marked positive inotropic effect was seen for 15 minutes to one hour. These toxic doses of strophanthin-G were decreased in the presence of exogenous adrenaline 10-6g/ml. The same result was observed in the case of rabbit atria excised from animals pretreated with reserpine 1mg/kg subcutaneously injected. In some cases the rabbit atria which were pretreated with larger dose of reserpine, did not contract in Locke's solution. Strophanthin-G could not resume the arrest of beating of these atria, but adrenaline could. The atrial contractions resumed by added adrenaline continued even after the added adrenaline was washed out, probably by the utilization of a small amount of adrenaline uptake into the atrial tissue. When strophanthin-G was added to the bath containing these atria, strophanthin-G showed a positive inotropic effect. The atria which continued to contract by a small amounts of adrenaline uptake, were stopped by more doses of strophanthin-G than in the cases of normal atria.
The positive inotropic effect of strophanthin-G on guinea-pig atria was notmutually synergistic with added adrenaline, while the effect of nicotine was markedly augmented in the presence of strophanthin-G, and in the presence of l-methionine the positive inotropic effect of strophanthin-G was strengthened.
From the above results, it was concluded that the positive inotropic effect of strophanthin-G was developed in the presence of the small amount of endogenous available catecholamine, and the toxic effect of strophanthin-G on the atria was decreased in the cases of exhaustion of endogenous as well as exogenous catecholamine.
