Micropuncture studies of the effects of acetazolamide on nephron function in the rat

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Abstract
Micropuncture experiments were performed on rats infused intravenously with acetazolamide in isotonic saline and compared with control experiments in rats infused at the same rate with isotonic saline. Fractional volume reabsorption increased 25% over control measurements in the surface proximal convoluted tubules concomitant with 25% fall in inulin clearance measured in final urine. The tubular fluid-to-plasma ratio (TF/P) for chloride averaged 1.15 [plus or minus] .019 SEM in the middle third of the proximal tubule in the saline infused rats and 0.92 [plus or minus] .017 SEM in rats infused with acetazolamide. TF/P for bicarbonate calculated from the chloride data increased to 1.5-2.0 at 60% of proximal tubular length, whereas 30-50% of filtered HCO3 was excreted in the bladder urine of the acetazolamide-treated rats. In these same animals the urine was virtually free of Cl ion. In the acetazolamide-infused animals, active Na transport in the proximal tubule continued with increased Cl reabsorption in the proximal tubule compensating for a decreased H ion secretion. Distal nephron reabsorption of Na with Cl continued apparently to the limits of Cl availability in tubular urine. No evidence for net bicarbonate reabsorption in the distal nephron was obtained.

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