SODIUM SENSITIVITY OF BLOOD-PRESSURE IN HYPERTENSIVES IS NOT RELATED TO SODIUM, BUT RATHER TO RENIN

Objective: To investigate whether a certain degree of sodium-sensitivi ty of blood pressure (BP) in essential hypertensives during sodium res triction is related to cumulative sodium loss. Methods: One-hundred an d seventeen untreated essential hypertensives were admitted to a metab olic ward for 7 days and put on a sodium restricted diet of 55 mmol/da y, During these 7 days urinary excretions of sodium, potassium and cre atinine were determined daily along with mean arterial pressure (MAP) and weight, Active plasma renin concentration (APRC), aldosterone (ALD O), renal plasma flow (RPF) and plasma volume (PV) were assessed after 7 days under steady state condition. The population was divided into tertiles based on the final changes in BP after 7 days. Results: Terti le 1 displayed a median fall in MAP of -13 (-42 to -9) mm Hg, whereas in tertile 2 and 3 a fall of -6 (-9 to -4) mm Hg and a rise of +1 (-3 to +11) mm Hg respectively, was encountered, Baseline characteristics were comparable between the tertiles, When tertile 1 was compared to t ertile 3 no significant differences between these tertiles were found with respect to cumulative sodium and potassium balances and weight lo ss. Furthermore, APRC levels were significantly higher in tertile 3 as compared to tertile 1 (22 and 27 mU/l respectively). Renal vascular r esistance (RVR) tended to be higher in tertile 3, although this was no t statistically significant, Aldo, RPF and PV were comparable between the tertiles. Conclusions: In contrast with tertile 1, MAP in tertile 3 is maintained at its original level, despite comparable sodium losse s. In tertile 3, however, levels of renin are higher compared to the g roup that is more sodium-sensitive. Therefore, our data suggest that t he degree of sodium-sensitivity of BP in essential hypertensive subjec ts is not determined by sodium status, but rather by renin.