Role of endothelin in mediating the attenuated renal hemodynamics in Dahl salt-sensitive hypertension.

The aim of this study was to evaluate the role of endothelin (ET) in the hypertension associated with giving a high sodium diet in Dahl salt-sensitive (DS) rats. To achieve this goal, we examined the effects of intravenous infusion of the nonspecific ET(A)-ET(B) antagonist on arterial pressure and renal function in conscious, chronically instrumented DS and Dahl salt-resistant (DR) rats. After 3 weeks on a high sodium (8%) diet, mean arterial pressure (MAP) in DS rats (166+/-3 mm Hg) was significantly higher than in DR rats (124+/-3 mm Hg). Baseline glomerular filtration rate (GFR) and renal plasma flow (RPF) in DS rats (1.92+/-0.25 mL/min and 7.07+/-0.80 mL/min) were lower than in DR rats (2.52+/-0.21 mL/min and 7.98+/-0.85 mL/min), respectively. Renal vascular resistance was significantly higher in DS rats (32.78+/-5.88 mm Hg x mL(-1) x min(-1)) than in DR rats (24.60+/-5.04 mm Hg x mL(-1) x min(-1)). Intravenous infusion of the ET antagonist SB 209670 at a dose of 30 microg x kg(-1) x min(-1) for 75 minutes caused a significant decrease in MAP in DS rats (from 166+/-3 to 144+/-4 mm Hg). In contrast, the effect of the ET antagonism on MAP in DR rats was not significant. ET-antagonist infusion tended to improve GFR and RPF in DS but not in DR rats. To determine the renal effects of ET antagonism independent of the systemic hemodynamic responses, we examined the effects of the same ET antagonist in rats chronically implanted with a renal interstitial catheter. Arterial pressure in DS rats (181+/-5 mm Hg) was significantly higher than in DR rats (135+/-3 mm Hg). Renal interstitial infusion of SB 209670 at a dose of 200 ng x kg(-1) x min(-1) for 60 minutes caused no change in MAP in DS or DR rats. Intrarenal ET antagonism significantly increased GFR (25%), RPF (30%), urine flow (32%), and urinary sodium excretion (25%) in DS rats, while it had no significant effect in DR rats. Fractional excretion of sodium was not significantly changed by renal interstitial infusion of the ET antagonist in DS rats, indicating that improved renal excretory function in DS rats is most likely due to the associated improvement in renal hemodynamics. We conclude that ET may play a role in the attenuated renal hemodynamics and possibly the development of Dahl salt-sensitive hypertension.