The relation between noradrenaline content of rabbit heart muscle and the amount of k-strophanthin needed to produce arrhythmias

Possible relations between the sensitivity of the heart to the arrhythmia-inducing property of k-strophanthin and myocardial storage of noradrenaline were investigated. Sensitivity to the glycoside was increased in rabbits pretreated with reserpine in doses which depleted noradrenaline, but not in rabbits pretreated with tyramine in doses which are known to reduce noradrenaline content. Sensitivity to the glycoside was restored to normal by an infusion of noradrenaline not earlier than 72 hr after reserpine treatment, but not by an infusion given at 24 hr. Infusion of noradrenaline did not itself reduce the sensitivity to k-strophanthin in normal rabbits. The glycoside acutely reduced the myocardial store of adrenaline and noradrenaline in normal rabbits. The possibility that cardiac sensitivity to k-strophanthin is regulated by bound but not by unbound noradrenaline is discussed.