Collecting duct-derived endothelin regulates arterial pressure and Na excretion via nitric oxide

Abstract

Mice with a collecting duct-specific deletion of endothelin-1 are hypertensive and have impaired Na excretion. Because endothelin-1 activates NO synthase (NOS) in the collecting duct, we hypothesized that impaired renal NO production in knockout mice exacerbates the hypertensive state. Control and knockout mice were treated chronically with N(G)-nitro-l-arginine methyl ester, and blood pressure (BP) and urinary nitrate/nitrite excretion were assessed. On a normal Na diet, knockout systolic BP was 18 mm Hg greater than in controls. N(G)-nitro-l-arginine methyl ester increased BP in control mice by 30 mm Hg and 10 mm Hg in collecting duct-specific deletion of endothelin-1 knockout mice, thereby abolishing the difference in systolic BP between the groups. A high-Na diet increased BP similarly in both groups. Urinary nitrate/nitrite excretion was lower in knockout mice than in controls on normal or high Na intake. In separate experiments, renal perfusion pressure was adjusted in anesthetized mice, and urinary nitrate/nitrite and Na excretion were determined. Similar elevations of BP increased urinary Na and nitrate/nitrite excretion in control mice but to a significantly lesser extent in knockout mice. Isoform-specific NOS activity and expression were determined in renal inner medulla homogenates from control and knockout mice. NOS1 and NOS3 activities were lower in knockout than in control mice given normal or high-Na diets. However, NOS1 or NOS3 protein expressions were similar in both groups on normal or high-Na intake. These data demonstrate that collecting duct-derived endothelin-1 is important in the following: (1) chronic N(G)-nitro-l-arginine methyl ester-induced hypertension; (2) full expression of pressure-dependent changes in sodium excretion; and (3) control of inner medullary NOS1 and NOS3 activity.

Figure 1

Effect of L-NAME (1 mg/ml in drinking water) on systolic arterial pressure in CD ET-1 KO and Flox control mice (n=6 each group) on a normal and high Na intake. Radiotelemetry devices were implanted in mice and arterial pressure assessed daily on the varying diets. *P<0.005 vs. flox control same day; †P<0.05 vs. flox control same day.

Figure 2

Urinary nitrate/nitrite excretion in Flox control and CD ET-1 KO mice (n=6 each group) on a normal and high Na diet. *P<0.05 vs. control on same diet; †P<0.05 vs. normal Na diet in same mouse genotype.

Figure 3

Panel A: Mean arterial blood pressure in Flox control (n=7) and CD ET-1 KO mice (n=6) during baseline (‘low’ pressure), after ligation of celiac and mesenteric arteries (‘medium’) and after ligation of the abdominal aorta below the renal arteries (‘high’). Panel B: Heart rate in Flox control and CD ET-1 KO mice during periods of low, medium, and high blood pressure. Panel C: Glomerular filtration rate (GFR) in Flox control and CD ET-1 KO mice during periods of low, medium, and high blood pressure.

Figure 4

Panel A: Urinary excretion volumes in Flox control (n=7) and CD ET-1 KO mice (n=6) during periods of low, medium, and high blood pressure. Panel B: Urinary Na excretion in Flox control mice and CD ET-1 KO mice during periods of low, medium, and high blood pressure. Panel C: Urinary ET-1 excretion in Flox control and CD ET-1 KO mice during periods of low, medium, and high blood pressure. Panel D: Urinary nitrate/nitrite (NOx) excretion in Flox control and CD ET-1 KO mice during periods of low, medium, and high blood pressure.

Figure 5

Panel A: Isoform-specific NOS activity in renal inner medullary homogenates from Flox control (n=8) and CD ET-1 KO mice (n=8) during normal salt (NS) and high salt (HS) diets. *P<0.05 vs. Flox control on the same diet; †P<0.05 vs. normal Na diet in same mouse genotype.