Detection of a circulating inhibitor of the Na+-K+-Cl− cotransport system in plasma and urine after high salt intake

The aim of the study was to detect the presence of an endogenous Na+-K+-Cl− cotransport inhibitor factor in plasma and urine from salt-loaded subjects. Twenty-six essential hypertensive patients (13 men, 13 women) and 6 normotensive controls (2 men, 4 women) received a diet containing 260 mmollday of NaCl tablets for 7 days. Human erythrocytes from healthy blood donors (using bumetanide-stimulated Li+ efflux) were used to test the inhibition of Na+-K+-Cl− cotransport by different plasma and urine concentrations collected the last day of the salt-loaded period. The addition of plasma and urine from salt-loaded subjects significantly inhibited erythrocyte Na+-K+-Cl− cotransport (P< .001). No differences were observed between hypertensive patients and normotensive controls. These results provide evidence of an Na+-K+-Cl− cotransport inhibitor factor in plasma and urine from salt-loaded humans, in concordance with previous reports in salt-loaded rats.