Pharmacological and biochemical evidence for the existence of two categories of dopamine receptor.

Evidence supporting the validity of the 'two dopamine receptor' hypothesis is presented. The availability of the 'first generation' of selective agonists and antagonists of the D-1 and the D-2 dopamine receptors provides pharmacological support for the hypothesis. The demonstration that stimulation of the D-2 receptor either inhibits or has no effect upon adenylate cyclase activity while stimulation of the D-1 receptor enhances cAMP formation provides biochemical support for the hypothesis. Finally, binding assays demonstrating two affinity states for the D-1 and the D-2 receptors are briefly discussed.