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Abstract

Dual action of acetazolamide and furosemide on proximal volume absorption in the rat kidney. Isotonic fluid absorption from the proximal convolution of the rat kidney was measured, using the Gertz shrinking droplet method, with simultaneous perfusion of the adjacent peritubular capillaries. The capillary perfusate consisted of a modified Ringers solution, containing either bicarbonate buffer or the sulfonamide buffer, glycodiazine. Different amounts of acetazolamide or furosemide were added to the perfusate. It was found that: 1) equimolar concentrations (30 mM) of glycodiazine are as effective as bicarbonate in promoting proximal isotonic reabsorption; 2) acetazolamide, at either 10^-5 or 10^-4 M, inhibited absorption to a greater extent when tested in the bicarbonate-containing solution, but the same level of inhibition was attained when the inhibitor was tested in the glycodiazine-buffered solution at a dose level of 10^-3 M; 3) The action of furosemide resembled that of acetazolamide except that, in either buffer, furosemide was a less potent inhibitor of reabsorption.
It is concluded that both acetazolamide and furosemide inhibit isotonic reabsorption by inhibiting carbonic anhydrase; at a slightly higher dose level, these agents also interfere with some other non-carbonic anhydrase-mediated process. Since neither acetazolamide nor furosemide in the tested doses exhibit an effect on cortical Na-K-ATPase, it is suggested that a direct inhibition of the H⁺ transporting system may occur.