FACTORS ASSOCIATED WITH ACUTE SALT-SENSITIVITY IN BORDERLINE HYPERTENSIVE PATIENTS

The acute sensitivity to sodium loading has been investigated in 26 borderline hypertensive patients (BHT) undergoing acute i.v. NaCl infusion. Measurements included blood pressure (BP), forearm vascular reistance (FVR) and venous distensibility (VV30), plasma renin activity (PRA), plasma aldosterone, plasma atrial natriuretic factor (ANF), and plasma levels of endogeneous Na+/K+ ATPase inhibitor. Sodium loading was associated with a greater than 8% increase in mean BP in 12 patients defined as salt-sensitive (NaCl-SENS) in comparison to salt-insensitive (NaCl-INSENS) subset. NaCl-SENS patients in comparison to NaCl-INSENS exhibited 1) a greater baseline VV30 (2.1 vs 1.4 ml/100 ml;p<.005), and a response to saline characterized by 2) increased FVR (21.4 vs -6.5 %;p<.005), 3) blunted PRA suppression (-42 vs -67 %;p<.05), 4) delayed ANF response and 5) release of a Na+/K+ ATPase inhibitor. Post-loading cumulative urinary sodium excretion was reduced in NaCl-SENS borderline hypertensives compared to NaCl-INSENS (2.6 vs 3.8 umol/min/Kg;p<.05). We conclude that acute salt-sensitivity in BHT is characterized by a blunted hormonal response to sodium loading which could be responsible of the activation of hemodynamic as well as humoral mechanisms leading to progressive blood pressure increase.