Effect of dopamine on NaCl transport in the medullary thick ascending limb of the rat

The aim of the present study was to determine whether dopamine affects NaCl reabsorption in the medullary thick ascending limb of the loop of Henle. Basolateral dopamine (10(-6) M) significantly inhibited Cl- reabsorption in the in vitro microperfused rat medullary thick ascending limb by 21 +/- 2% (P < 0.01). The response to 10(-6) M dopamine was completely blocked by pretreatment with the dopamine D-1 receptor antagonist R(+)-SCH-23390 (5 x 10(-5) M), and was mimicked by the dopamine D-1 receptor agonist A-77636 (10(-6) M; Delta-36 +/- 2%; P < 0.05). In contrast, basolateral administration of the dopamine D-2 receptor agonist (+)-bromocriptine (10(-6) M) transiently increased Cl- reabsorption by 49 +/- 18% (P < 0.05). Neither the D-1 nor the D-2 agonist affected Cl- reabsorption when selectively administered to the luminal membrane. These data suggest that the predominant effect of dopamine on the medullary thick ascending limb of the rat is to inhibit the reabsorption of NaCl, a response which is mediated by dopamine D-1 receptors. (C) 1998 Elsevier Science B.V.