[Sympathetic modification of the relationship between salt intake and blood pressure in the general population]

Using pulse rate and urinary sodium as indices of sympathetic tone and salt intake, respectively, we investigated whether both an increased sympathetic activity and a high salt consumption are needed to increase blood pressure in the population at large. A random population sample of 2081 subjects with a minimum age of 18 years was stratified by tertiles of pulse rate. In subjects with a slow and in those with a fast pulse rate, a significant curvilinear relation between blood pressure and urinary sodium was found, while in the middle pulse rate third the correlation was not significant. A significant interaction between pulse rate and urinary sodium indicated that, when urinary sodium increased from 160 to 300 mmol/24 h, both systolic and diastolic pressure rose in subjects with a fast pulse rate, but declined in those with a slow pulse rate. In conclusion, our results suggest that a high salt intake is associated with an elevated blood pressure in subjects with a high sympathetic tone, but with a decreased pressure in individuals with a low sympathetic activity.