Nitric oxide, salt sensitivity, and cardiorenal injury in hypertension

A connection between salt sensitivity and hypertension seems certain, but a number of issues remain unresolved, e.g., the mechanisms involved in salt sensitivity, its role in pathogenesis and/or maintenance of hypertension, and its ability to predict cardiorenal risk. The role of nitric oxide (NO) has been studied extensively. Evidence shows that NO, along with the vasoactive substances angiotensin II and endothelin-1, is important in modulating vascular tone. In addition, imbalances among these substances may participate in the abnormal cardiovascular and renal remodeling that occurs in hypertension. What causes such imbalances remains unclear. Animal studies show that in salt-sensitive subjects, the activity of NO synthase (NOS) fails to upregulate in response to increases in blood pressure, but that such activity upregulates rapidly in similar circumstances in non-salt-sensitive subjects. Human studies of essential hypertensives have shown an association between salt sensitivity and a number of conditions, including impaired endothelium-dependent relaxation mediated by NO, insulin resistance, microalbuminuria, and ventricular hypertrophy and cardiovascular events. These findings have intriguing implications in regard to whether, in hypertension, salt sensitivity might be a marker of increased cardiovascular and renal risk that is linked to abnormalities in the bioactivity of NO.