Dopamine (3, 4-dihydroxyphenylethylamine)
Dopamine (3, 4-dihydroxyphenylethylamine) is an endogenous catecholamine and immediate precursor of nor adrenaline.
Dopamine is a unique catecholamine which has both direct (α and β actions) and indirect (release of nor adrenaline) actions. In addition it also has dopaminergic (D1and D2 receptor actions.
The cardiovascular effects of dopamine are mediated by different receptors that vary in either affinity for the dopamine.
At very low IV doses (0.5-2µg/kg/min) dopamine acs predominantly on vascular D1, dopaminergic receptors and dilates the renal, mesenteric and coronary vascular beds. This results in increase in renal blood flow, glomerular filtration rate and Sodium excretion.
At somewhat higher IV doses (2-10µg/kg/min) dopamine also stimulates β1 receptors on heart and releases noradrenaline from sympathetic nerve terminals. This exerts a positive inotropic but little chronotropic effects on heart. It increases the blood pressure, but the vascular resistance is unaffected.
At high dose (10µg/kg/min) dopamine activate vascular α1 effects leading to vasoconstriction, which counters the useful effects of dopamine.
Dopamine has no effect on non vascular α and β receptors. Exogenous dopamine has no central effects as it cannot cross the BBB.
Dopamine is useful in the treatment of cardiogenic or septic shock, oliguria and severe congestive heart failure.