Higher Salt Consumption, Digoxin-like Factor, and Nifedipine Response Are Associated With Salt Sensitivity in Essential Hypertension

In addition to demonstrating evidences of increased sympathetic nervous system activity and marked left ventricular hypertrophy in salt-sensitive hypertensives, our group has also reported increased weight gain with salt overload in these patients. The increased weight gain suggests volume expansion, a situation already shown to increase plasma levels of a Na, K-ATPase inhibitor. Therefore, in the present study, digoxin-like factor (DLF) serum levels, spontaneous salt ingestion, nifedipine hypotensive effect, and plasma renin activity were evaluated in essential hypertensive subjects. Thirteen essential hypertensive outpatients were studied sequentially on an ad lib diet, a low salt diet (LSD = 30 mEq Na/day), and a high salt diet (HSD = LSD + 171 mmol/L NaCl/day), 1 week each. On the seventh day of LSD and HSD, DLF levels, mean blood pressure (MBP) response to nifedipine (10 mg sublingual), and plasma renin activity were measured. The MBP percent change from the seventh day of LSD to the seventh day of HSD (salt sensitivity) ranged from −13.7 to 20.9%. A positive correlation (r = 0.64, P < .01) was observed between salt sensitivity and 24-h urinary sodium excretion with an ad lib diet. The DLF serum levels correlated with the salt sensitivity both on LSD (r = 0.50, P < .05) and on HSD (r = 0.53, P < .05). Salt sensitivity was positively correlated with the difference of response to nifedipine between HSD and LSD (r = 0.78, P < .001). Plasma renin activity correlated inversely with DLF on LSD (r = −0 . 5 1 , P < .05). In conclusion, salt sensitivity is associated with increased salt consumption, higher DLF serum levels, and increased nifedipine hypotensive effect during salt loading. Am J Hypertens 1992;5:707-712