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During the past decade, it has become evident that dopamine plays an important role in the regulation of renal function and blood pressure. Dopamine exerts its actions via a class of cell-surface receptors coupled to G-proteins that belong to the rhodopsin family. Dopamine receptors have been classified into two families based on pharmacologic and molecular cloning studies. In mammals, two D₁-like receptors that have been cloned, the D₁ and D₅ receptors (known as D_1A and D_1B, respectively, in rodents), are linked to stimulation of adenylyl cyclase. Three D₂-like receptors that have been cloned (D₂, D₃, and D₄) are linked to inhibition of adenylyl cyclase and Ca²⁺ channels and stimulation of K⁺ channels. All the mammalian dopamine receptors, initially cloned from the brain, have been found to be expressed outside the central nervous system, in such sites as the adrenal gland, blood vessels, carotid body …