Abstract
Reserpine pretreatment of cats abolished the action of ephedrine to induce spontaneous beating in papillary muscles obtained from these animals. This spontaneous beating was viewed as resulting solely from catechol amine release. The positive inotropic action of ephedrine was diminished but not abolished by reserpine pretreatment. Reserpine reduced the heart rate in vivo, but it did not affect the peak contraction height or the rate of failure of the isolated papillary muscle. The contractile response to adrenaline (0.1 mug/ml.) was not affected by reserpine pretreatment. However, in this concentration adrenaline induced spontaneous beating only after reserpine.