Factors that determine the response of people with mild hypertension to a reduced sodium intake.

One hundred and eighty-six males who had had 3 run-in visits entered the study with a supine diastolic BP 95-110 mm Hg. This was followed by 3 pretreatment and 3 post-treatment visits. One hundred and sixty patients were given advice to reduce sodium intake after visit 3, and twenty-six patients served as control. In the control group there were relatively insignificant changes between the pre and post visits. In the diet group blood pressure fell by 13/9 mm Hg; urine sodium from 168 to 85 mmol/day and plasma renin activity rose from .50 to .77 ng AI/ml/h. Regression analysis showed that the only cross-sectional correlations were PRA with age, urine sodium and plasma potassium. There were highly significant correlations between the change in urinary sodium and the change in blood pressure and between the changes in blood pressure and plasma renin activity. Multiple Regression Analysis indicated that the final diastolic blood pressure achieved depended upon the initial diastolic blood pressure, the fall in sodium intake, and was reduced by the rise in plasma renin activity. Patients who responded to sodium restriction had a lower initial renin value than other patients. This study emphasises the importance of the interaction between sodium, potassium and renin in the determination of blood pressure levels.