1964 Volume 16 Issue 4 Pages 262-270
When the rabbit atria arrested in vitro by reserpine 3×10-5 (g/ml) were kept in the reserpine containing Locke's solution for 60 to 90 minutes, the atrial contractions did not resume spontaneously even after bath fluid was repeatedly changed.
Thus reserpine treated atria could be resumed by l-, d- or ld-methionine 10-3, Catron 10-5, strophanthin-G 10-6, ephedrine 10-4 or tyramine10-4. However, in the case of the atria excised from rabbit pretreated with reserpine 1mg/kg these drugs could not resume the atrial contractions arrested by the above described reserpine (3×10-5) action.
The stimulant actions of nicotine 10-5 to 10-4 on the normal atria were potentiated in the presence of l-, d- or ld-methionine 10-4 or strophanthin-G 10-6 but depresseds in the presence of ephedrine 10-5 or tyramine 10-6. The atrial contractions were augmented by l-, d- or ld- meth ionine 10-3, strophanthin-G 10-6, ephedrine 10-6 or tyramine 10-6.
The atria excised from rabbits pretreated with reserpine 1 mg/kg did not respond to tyramine in any concentration, and the effects of ephedrine 10-5 on these atria were weaker than that on the normal atria.
l-Ethion ine 10-4 to 10-3, glutathione 10-4 as well as l-cysteine 10-4 showed no remarkable effect on the normal atrial contractions, while l-ethionine 10-4 antagonized to the stimulant action of l-methionine 10-4 to 10-3 on the normal atria.
From these experimental results, it was assumed that methionine, stro phanthin-G, ephedrine or tyramine may affect the active mobilization of endogenous catecholamine in atria and that ephedrine or tyramine may stand in catecholamine receptors to compete with endogenous catecholamine, and it was discussed that ephedrine tachyphylaxis may be developed from the endogenous catecholamine-blocking action of ephedrine binding to the catecholamine receptors.
