Selective ETA Receptor Antagonism with ABT-627 Attenuates All Renal Effects of Endothelin in Humans

Endothelin (ET-1) acts as a potent vasoconstrictor in the human kidney, and this vasoconstriction could contribute to the ischemia seen in acute renal failure. In animal studies, the vasoactive properties of ET-1 are known to be ETA receptor- and/or ETB receptor-mediated; however, the receptor subtype involved in the human kidney remains to be defined. In a phase I, single-center, double-blind, randomized, three-period, crossover design, the effects of orally administered ABT-627, a selective ETA receptor antagonist, on renal hemodynamics during ET-1 infusion were evaluated. Two doses of ABT-627 (5 and 20 mg) were compared with placebo and nifedipine. For each dose level of ABT-627, a cohort of nine subjects was studied. A para-aminohippuric acid/inulin clearance test was performed once at the end of each 7-d treatment period. Infusion of ET-1 significantly decreased effective renal plasma flow, GFR, sodium excretion, and urine flow. Pretreatment with 20 mg of ABT-627 significantly decreased mean arterial pressure. In contrast, 7 d of treatment with both doses of ABT-627 did not affect baseline renal parameters. However, because mean arterial pressure decreased, a tendency toward a reduction of renal vascular resistance could indeed be demonstrated. Compared with placebo, both doses of ABT-627 were equally effective in blocking all renal effects caused by ET-1 infusion. In the model of exogenous ET-1 infusion, ABT-627 had a tendency to prevent ET-1-induced renal changes more effectively compared with nifedipine. The contribution of endogenous ET-1 and the ETA receptor in maintaining basal renal vascular tone in the human kidney is small. In addition, compared with placebo, selective ETA receptor antagonism with both doses of ABT-627 completely prevented all renal changes caused by ET-1 infusion.