Evidence for participation of catecholamines in cardiac action of ouabain. Release of catecholamines

Ouabain induces an increase in loss of radioactive material from guinea pig atria loaded either in vitro or in vivo with radioactive noradrenaline. The increased loss of radioactivity is paralleled by an increase in pacemaker activity. This effect of ouabain is similar to the effect of tyramine studied under comparable conditions. Arteficial pacing does not increase the rate of loss of radioactivity. It is concluded that ouabain releases catecholamines and/or inhibits reuptake of catecholamines, and that the positive chronotropic effect is linked to an increase in catecholamine concentration in the vicinity of the pacemaker.