How is mechanism of action of dopamine (a1 and b1)?

Dopamine can activate: 1- α1 and β1 adrenergic receptors - at higher doses, it can cause vasoconstriction by activating α1 receptors, - at lower doses, it stimulates β1 cardiac receptors 2- D1 and D2 dopaminergic receptors - occur in the peripheral mesenteric and renal vascular beds binding of dopamine produces vasodilation. Dopamine is rapidly metabolized to homovanillic acid by MAO or COMT These D1 and D2 receptors are not affected by α- or β-blocking drugs