Inhibition of inducible nitric oxide synthase during high dietary salt intake

Abstract

Background: Previous studies indicate that nitric oxide (NO) is involved in the regulation of blood pressure (BP) and natriuresis in response to high sodium intake. We investigated the role of inducible NO synthase (iNOS) in response to an increased salt intake. Methods: Conscious, chronically catheterized rats were exposed to a high-salt (6%) diet for 14 days while receiving vehicle or aminoguanidine ([AG]; 250 mg/kg/24 h), which selectively inhibits iNOS. A group of rats on normal salt intake + AG were also studied. Results: Aminoguanidine had no impact on BP (120 ± 2 v 116 ± 1 mm Hg, control v day14) or 24-h urinary nitrite and nitrate excretion (U NOxV), in rats on normal salt but prevented lipopolysaccharide-induced hypotension. High salt alone had no impact on BP (120 ± 1 v 121 ± 1 mm Hg), whereas U NaV (1.3 ± 0.2 v 3.5 ± 0.6 μeq/min, P < .001) and U NOXV increased with high salt intake. The natriuretic response persisted (1.5 ± 0.2 v 4.3 ± 0.8 μeq/min, P < .005), but the increase in U NOXV was prevented with chronic AG although BP fell slightly (121 ± 1 v 115 ± 1 mm Hg, P < .05). There was no change in plasma volume with high salt, and 24-h U NaV increased appropriately in the presence of AG. The in vitro NOS activity was not increased in kidney homogenates by high salt diet, nor was it affected by chronic AG treatment. Conclusion: We conclude that NO from an iNOS source is not essential for the regulation of sodium excretion and BP in the presence of a high-salt diet in a normal rat.