Nitric oxide inhibition as a mechanism for blood pressure increase during salt loading in normotensive postmenopausal women

Objectives: Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide (NO), which plays an important role in natriuresis. We determined whether changes in endothelium-dependent vasodilation (EDD) and plasma ADMA predict changes in blood pressure (BP) after salt loading in normotensive postmenopausal women (PMW). Methods: In 15 normotensive PMW (age 50-60 years), not receiving estrogen, ambulatory 24-h BP, plasma lipids, and ADMA were measured after 4 days of a low-salt diet (70 mEq/day) and following 7 days of high-salt intake (260 mEq/day). Brachial artery diameter at rest, during reactive hyperemia, i.e. EDD, and after sublingual nitroglycerin, i.e. non-EDD, were measured by ultrasound. The 24-h urinary NO metabolite (NOx) was measured by Griess reaction. Plasma ADMA was measured by high-pressure liquid chromatography. Results: During low-salt, 24-h BP levels averaged 121 ± 11 and 69 ± 7 mmHg for systolic BP (SBP) and diastolic BP (DBP), respectively. After salt loading, average 24-h BP increases were: 7.6 mmHg for SBP, 2.2 mmHg for DBP, and 5.5 mmHg for pulse pressure (PP). Increases of 24-h SBP and 24-h PP after salt loading correlated directly with changes in ADMA (partial R² = 0.16 for 24-h SBP and 0.17 for 24-h PP, P < 0.05 for both) and inversely with changes in EDD (partial R² = 0.13, P = 0.09 for 24 h SBP and partial R² = 0.15, P = 0.07 for 24-h PP), after adjustment for age and cholesterol. Conclusions: Inhibition of NO bioavailability by ADMA and a subsequent reduction in EDD contribute to the increase in BP during high-salt intake in normotensive PMW not receiving estrogen.