RENAL SODIUM HANDLING AND SODIUM-TRANSPORT INHIBITOR IN SALT-SENSITIVE ESSENTIAL-HYPERTENSION

To investigate the mechanism whereby blood pressure rises with NaCl loading in salt-sensitive essential hypertension, salt-sensitivity index was determined along with sodium and lithium clearances, plasma Na+,K+-ATPase inhibitor and intra-erythrocyte sodium and potassium concentrations. Salt-sensitivity index was defined as the percentage of change in mean blood pressure when NaCl intake was changed from low (34 mmol/day) to high (342 mmol/day). Salt-sensitivity index was inversely correlated with fractional excretion of lithium both on the low and high NaCl diets (r = -0.721, P < 0.01 and r = -0.591, P < 0.02, respectively; n = 16), but not with fractional excretion of sodium. The change of plasma Na+,K+-ATPase inhibition with NaCl loading had a direct correlation with salt-sensitivity index (r = 0.704, P < 0.01; n = 16). Either intra-erythrocyte sodium and potassium concentrations or the ratio of these two values did not change significantly with an increase of dietary NaCl intake. These results suggest that an enhancement of proximal tubular sodium reabsorption stimulates secretion of plasma Na+,K+-ATPase inhibitor which may be involved in a rise in blood pressure with sodium loading. They also suggest that lithium clearance is a determinant which can predict salt sensitivity without actual NaCl loading.