Abstract

The stop flow technique was used to investigate the effect of bendroflumethiazide (BHFT) on sodium, chloride and potassium transport in distal areas of the dog nephron. Distal sodium and chloride reabsorption was retarded. Increasing plasma sodium and chloride concentrations increased the magnitude of this effect, but increasing the length of ureteral occlusion decreased it. BHFT did not affect chloride reabsorption in the presence of exogenous sulfate but did affect sodium reabsorption. BHFT raised stop flow urine to plasma (U/P) potassium ratios and increased the apparent length of the nephron segment secreting potassium. Increasing the supply of exchangeable sodium enhanced the former response to the drug. We conclude that BHFT primarily inhibits sodium reabsorption in the distal tubule. The effect upon chloride reabsorption may be indirect, resulting from the inhibition of sodium transport. The effect of carbonic anhydrase inhibition by BHFT upon potassium excretion could not be completely assessed. The results suggest that BHFT may, in addition to other means, increase potassium excretion by increasing the supply of exchangeable sodium and by increasing the length of nephron segment secreting potassium. This latter effect does not seem to be related to carbonic anhydrase inhibition.