Pharmacological analysis of positive chronotropic and inotropic responses to etilefrine in isolated dog heart preparations.

Positive chronotropic and inotropic responses to etilefrine (alpha-[(ethylamino)methyl]-m-hydroxybenzyl alcohol), an orally active cardiovascular agent, were investigated in isolated dog right atrial and left ventricular preparations. Intravenous administration of etilefrine to a support dog increased heart rate and mean systemic blood pressure, and increased sinus rate and atrial contractile force in the isolated right atrium perfused with blood from the support dog. Etilefrine injected intra-arterially to isolated atria and ventricles induced dose-dependent positive chronotropic and inotropic effects. Etilefrine was about 100 times less potent than isoproterenol. The effects of etilefrine in isolated atria were significantly inhibited by treatment with atenolol, but were not significantly inhibited by ICI 118,551. The effects of etilefrine were partially inhibited by imipramine. These results indicate that etilefrine is a highly selective beta-1 adrenoceptor agonist and suggest a moderate catecholamine-releasing activity by tyramine-like action in the blood-perfused dog heart.