Renal effects of bumetanide

Upon administration of bumetanide in normal human subjects, both glomerular filtration rate and effective renal plasma flow were increased, in approximately proportional amounts. Sodium excretion rose to 16 per cent of filtered load, whereas there was a chloriuresis of 23 per cent. During maximal water diuresis, the drug caused an increase in urine flow rate associated with a rise in osmolal clearance and no change in solute-free water clearance. Intravenous injection of the drug during hypertonic saline infusion into hydropenic subjects resulted in the virtual abolition of water abstraction from the collecting duct. The drug caused a modest increase in phosphate excretion but no change in the percentage of filtered bicarbonate excreted. Furthermore, neither urinary pH nor net hydrogen ion excretion was altered by the drug. The data suggest that bumetanide has its major action in the loop of Henle but that it also inhibits sodium transport in the proximal tubule. In addition, the nature of the proximal action does not appear to be related to a carbonic anhydrase inhibitory effect. These latter observations regarding the proximal action of the drug were verified by micropuncture studies performed in the dog.
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