Dopamine is preferred over dobutamine in treatment of shock with oliguria because:-

Dopamine is the drug of choice for cardiogenic shock with oliguric renal failure. It acts on D1 (at a dose of 1-2 mg/kg/ min.), b1 (at 2-10 mg/kg/min.) and a1 (at > 10 mg/kg/min.) receptors. It causes renal vasodilation by acting on D1 receptors and maintains renal perfusion and GFR. Other ionotropic agents like NA cause renal vasoconstriction and thus worsen renal failure.