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

The aim of the present study was to determine whether vasopressin affects NaCl reabsorption in the medullary thick ascending limb of the loop of Henle when administered selectively to the luminal membrane. At 5 x 10(-6) M and 10(-8) M, luminal [Arg(8)]vasopressin significantly inhibited Cl- transport in the in vitro microperfused rat medullary thick ascending limb by 46.4 +/- 5.9% (P < 0.01) and 32.4 +/- 2.0% (P < 0.05) respectively. The response to 10(-8) M luminal [Arg(8)]vasopressin was completely blocked by the vasopressin V-1 receptor antagonist [beta-mercapto-beta,beta-cyclopenta-methylenepropionyl(1),O-Me-Tyr(2),Arg(8)]vasopressin (10(-6) M), and was mimicked by the vasopressin V-1 receptor agonist [Phe(1),Ile(5),Om(8)]vasopressin (10(-8) M; Delta - 35.0 +/- 4.5%; P < 0.05). Luminal administration of the vasopressin V-2 receptor agonist [deamino-Cys(1),D-Arg(8)]vasopressin (5 x 10(-6) M) had no effect on transport. These data suggest that luminal vasopressin can inhibit NaCl transport in the medullary thick ascending limb of the rat via vasopressin V-1 receptors.