Changes in intrarenal sodium handling during saluretic treatment in patients with essential hypertension

The effect of 50 mg chlorthalidone on blood pressure, body fluid volumes and renal functional parameters was determined in 8 patients with essential hypertension. After 3 days there were signs of volume depletion with little change in mean arterial pressure (MAP). Maximal free water clearance (CH2O) was decreased and fractional proximal sodium reabsorption was increased, but no correlations between these parameters were found. After 3 months there was in inverse relationship between both changes in MAP and the indices of volume depletion and CH2O. It is concluded that when MAP decreases after prolonged saluretic treatment, there is a partial recovery of the initially induced volume depletion and less stimulation of proximal tubular sodium reabsorption. The continuing inhibitory action of chlorthalidone on "distal" sodium reabsorption is partially compensated for, probably by the stimulating effect at this site of the decrease in MAP.