Catecholamines increase activation of Ca2+ via beta-adrenergic receptors and the adenyl cyclase system.
Dopamine has both alpha and beta and dopaminergic effects. Its beta effects in the heart occur largely through the release of endogenous norepinephrine, which may be largely depleted in a failing heart. As such, the benefits of dopamine administration, if any, occur at low doses (e.g., 0.02 mg/kg per minute), where it may induce renal arterial vasodilatation. In general, it is employed in association with more potent inotropic agents (e.g., dobutamine).
Dobutamine characterized by an increase in cardiac output and a decrease in ventricular filling pressure with little change in heart rate. There is modest rise in arterial pressure and decrease in peripheral vascular resistance. The positive inotropic activity of dobutamine is mediated by direct stimulation of beta-adrenergic receptors in the myocardium.
Dobutamine infusion generally is begun at 2 µg/kg per minute and titrated to optimize cardiac output while reducing LV filling pressure. The major side effects of dobutamine are an excessive increase in heart rate with high doses and ventricular arrhythmias.