Background: Nitric oxide deficiency is involved in the development of hypertension, but the mechanisms are currently unclear. This study was conducted to further elucidate the role of neuronal nitric oxide synthase (nNOS) in blood pressure regulation and renin release in relation to different sodium loads.
Methods: Blood pressure and heart rate were measured telemetrically and assessed during periods of physical activity and inactivity. Urinary solute excretion was measured by metabolism cages and plasma renin concentration (PRC) was determined by radioimmunoassay; all in nNOS knockout (nNOS(-/-)) and wild-type (nNOS(+/+)) mice after 10 days of low (0.01% NaCl) and high (4% NaCl) sodium diets.
Results: The resting heart rate was reduced in nNOS(-/-) mice, but the two genotypes had similar blood pressure during the low (nNOS(+/+) 104 +/- 2 mm Hg; nNOS(-/-) 103 +/- 2 mm Hg) and high (nNOS(+/+) 107 +/- 3 mm Hg; nNOS(-/-) 108 +/- 2 mm Hg) sodium diets. During the high sodium diet, PRC did not differ between the genotypes (nNOS(+/+) 743 +/- 115 10(-5) Goldblatt units; nNOS(-/-) 822 +/- 63 10(-5) Goldblatt units), but during the low sodium diet, nNOS(-/-) mice failed to increase PRC (nNOS(+/+) 2164 +/- 220 10(-5) Goldblatt units; nNOS(-/-) 907 +/- 101 10(-5) Goldblatt units) and renal renin mRNA. On the low sodium diet, nNOS(-/-) mice also showed increased urine flow rate and osmolar excretion, observations not made during a high sodium diet.
Conclusions: Our results show that nNOS is necessary for stimulation of renin in response to sodium restriction. Furthermore, nNOS(-/-) mice are normotensive, and their blood pressure responds normally to an increased dietary sodium intake, indicating that nNOS deficiency does not cause salt-sensitive hypertension.