All of the components of a complete dopamine system are present within the kidney, where dopamine acts as a paracrine substance in the control of sodium excretion. Dopamine receptors can be divided into D 1 -like (D 1 and D 5 ) receptors that stimulate adenylyl cyclase and D 2 -like (D 2 , D 3 , and D 4 ) receptors that inhibit adenylyl cyclase. All 5 receptor subtypes are expressed in the kidney, albeit in low copy. Dopamine is synthesized extraneuronally in proximal tubule cells, exported

more »

... these cells largely into the tubule lumen, and interacts with D 1 -like receptors to inhibit the Na ϩ -H ϩ exchanger and Na ϩ ,K ϩ -ATPase, decreasing tubule sodium reabsorption. During moderate sodium surfeit, dopamine tone at D 1 -like receptors accounts for Ϸ50% of sodium excretion. In experimental and human hypertension, 2 renal dopaminergic defects have been described: (1) decreased renal generation of dopamine and (2) a D 1 receptor-G protein coupling defect. Both defects lead to renal sodium retention, and each may play an important role in the pathophysiology of essential hypertension. (Hypertension. 2001;38:297-302.)