Na+,K+,Cl- cotransport is a marker of distal tubular function in essential hypertension

To analyze the natriuretic and diuretic response to frusemide in 33 male essential hypertensive patients as a function of basal renal sodium handling and erythrocyte transport system.

The natriuretic and diuretic response to an oral dose of frusemide (25 mg) was assessed with a simplified method. Urinary sodium and water excretion were measured in the basal state and every 30 min after the frusemide dose for 240 min. Basal 24h urinary sodium and water excretion, Na+,K+,Cl- cotransport and Li+-Na+ countertransport were measured 24 h before the test.

There was a highly significant correlation between the natriuretic and diuretic response to frusemide and Na+,K+,Cl- cotransport and Li+-Na+ countertransport. After a multiple regression analysis the natriuretic and diuretic response to frusemide was not correlated with indices of proximal tubular function (Li+-Na+ countertransport, fractional uric acid excretion and the ratio of fractional sodium excretion to fractional uric acid excretion).

These results support the hypothesis that erythrocyte Na+,K+,Cl- cotransport is a marker of distal tubular function.