Cardiac Effects of Tyramine

The cardiac effects of tyramine ( p -hydroxyphenylethylamine) were studied in 22 dog heart-lung preparations. In six uncontrolled rate preparations, tyramine 250 to 500 µg. increased the heart rate an average of 21 per cent. In controlled rate preparations, tyramine 100 to 250 µg. consistently increased ventricular contractile force, cardiac output, and blood pressure; there was a consistent decrease of right and left atrial pressures. Comparable hemodynamic effects were produced by 1 to 2.5 µg. of levarterenol, except that the effects of tyramine tended to be of longer duration and were less likely to be followed by cardiac depression. It is concluded that tyramine has significant positive inotropic and chronotropic effects in the dog heart-lung preparation. In three animals pretreated with reserpine, tyramine had little effect. Its action appears to depend to a large extent upon the presence of myocardial catecholamines.