Effects of higenamine on isolated heart adrenoceptor of rabbit

In the present study, effects of higenamine on various mechanical parameters of rabbit left atria as influenced by propranolol were investigated and compared to those of epinephrine. The following results are obtained: Higenamine, in a dose-dependent manner, increased the rate of tension development and shortened both the time to peak tension and the total duration of contraction. These effects of higenamine were competitively blocked by propranolol. The pA2 values of higenamine and epinephrine against propranolol were 8.58 +/- 0.14, 7.50 +/- 0.82 respectively, and the slopes by Schild plots were 0.97 and 0.99 with higenamine and epinephrine, respectively. The results indicate that the positive inotropic action of higenamine is likely due to stimulation of cardiac adrenoceptors.