Plasma-renin response to isotonic volume contraction in young salt-sensitive normotensive men

Salt-sensitive persons have lower plasma renin activity than salt-resistant persons and their plasma renin activity increases less with a low sodium diet or volume depletion, compared to salt-resistant individuals. However, the time course of the renin response to acute volume contraction has not been studied in humans. Therefore, we designed an acute study in salt-sensitive and salt-resistant normotensive volunteers, in which we examined the renin response to isotonic volume contraction. Twenty-four previously characterized salt-resistant (n = 13) and salt-sensitive (n = 11) persons were placed on a high salt diet containing 280 mmol NaCl/day for 3 days. After an overnight stay, volume depletion (total, 300 mmol Na) was induced by furosemide infusion. Free water deficits were replaced by 5% isotonic glucose infusion. Blood was obtained for electrolytes, plasma renin activity, and plasma aldosterone concentration. Blood pressure (BP) and heart rate were monitored during the experiment. Intravascular volume depletion resulted in a progressive increase in plasma renin activity that was both steeper and higher in salt-resistant than in the salt-sensitive subjects (P < .001). There was a slight increase in BP in response to volume contraction in both groups. Although heart rate did not change in salt-sensitive persons, it increased significantly (P < .001) in the salt-resistant group. These findings point to an intrinsic difference in the regulation of renin release between salt-sensitive and salt-resistant subjects that may account for the different BP responses to changes in dietary sodium intake.