The effect of loop diuretics on fluid reabsorption from the rat proximal convoluted tubule

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Abstract
The effects of the ''loop diuretics'' bumetanide, furosemide and piretanide on fluid reabsorption from the rat proximal convoluted tubule have been tested to assess whether a Na+-Cl- co-transport mechanism can support fluid reabsorption from this nephron segment. Proximal convoluted tubules were perfused in vivo at 25 nl min-1 with chloride Ringer solutions containing [3H]inulin. Fluid reabsorptive rate (Jv) was 2.05 .+-. 0.07 nl mm-1 (n = 115) from control chloride Ringer. Bumetanide at 10-6 and 10-5 M reduced Jv by about 40%. Bumetanide at 10-7 M, furosemide (10-4 and 10-5 M) and piretanide (10-4 and 10-5 M) had no effect on Jv. At 10-3 M, furosemide and piretanide reduced Jv by about 45%. The results show that luminal application of loop diuretics lowers fluid reabsorption from the proximal convoluted tubule and the order of potency for inhibiting reabsorption is bumetanide > furosemide .tbd. piretanide. The specificity of the loop diuretics at their effective concentrations needs to be confirmed, however, before attribution of a role for Na+-Cl- co-transport in the support of proximal tubule fluid reabsorption.