VPT 321: Veterinary Neuropharmacology (2+1)

Catecholamine - Dopamine

DOPAMINE

Dopamine: (3, 4-dihydroxyphenylethylamine)

• It 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.