Abstract P396: Blood Pressure Of Individuals With Salt Sensitivity But Not Salt Resistance Is Increased After Acute Na + Loading

Abstract

Kidney function is influenced by salt intake and may adapt rapidly to dietary salt variations by modulating pressure-natriuresis. In particular, salt-sensitive (SS) individuals respond to a high-salt diet with a large rise in blood pressure (BP), indicative of a blunted pressure-natriuresis relationship, while 7-12% of the normotensive population have reduced BP with Na + loading, a condition termed inverse salt sensitivity. We compared effects of acute intravenous Na + loading on renal function in normotensive salt-resistant (SR) (11) and SS (5) individuals, as described below. After subjects were prepared in metabolic balance at 100 mmol Na + /d, they underwent Phase I renal function studies (0700h-1100h); Phase II oral sodium citrate load (1100h) followed by a continuous intravenous infusion of 0.9% saline (1100h-1300h); Phase III post-control monitoring period (1300h-1500h). During the entire protocol, BP and heart rate were monitored every 10 min. Blood and urine samples were obtained every hour and analyzed for Na + , K + , creatinine, osmolality and pH. Renal function tests included GFR, filtered Na + load (F Na ), urinary Na + exretion (U Na V), fractional Na + reabsorption (FR Na ), and fractional Na + excretion (FE Na ). Mean BP was calculated using 6 measurements/hour. SS systolic (SBP) and diastolic BP (DBP) were significantly higher than in subjects with SR throughout the procedure (at 1100h SS 137±6.3 vs SR 114±2.6 mmHg, p<0.001 two-way ANOVA). Phase II changes in BP were calculated by subtracting BP at 1100h; there were no significant changes for SR BP. With Na + infusion, SS SBP and DBP increased and remained elevated through the end of the procedure. The increase of SS DBP at 1500h was significantly higher than that of SR (85.8±5.5 vs 65.9±1.6 mmHg, p<0.05 t-test). Both GFR and F Na were increased in SR, while there were no changes in SS after Na + infusion (GFR SR Y=2.9*X-28.37; SS Y=0.61*X-11.45). FR Na was increased in SR, but decreased in SS. The difference between slopes was significant (SS Y=-1.92*X+21.56; SR Y=0.64*X-6.8, P<0.01). After 1 h of Na + loading, FE Na decreased to 1.3 in SS but increased to 1.6 in SR (P=0.089 t-test). The results indicate that renal function of individuals with SS responds differently to acute intravenous Na + loading than those with SR.