Estimation of Free Water Back Diffusion during Water Diuresis in Man Using Lithium Clearance and Furosemide Effect: Some Unresolved Questions
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The only way to localize tubular action of diuretics in man is by clearance techniques. The clearance of solute-free water (CH2O) is used to estimate NaCl reabsorption in the Loop of Henle and distal tubule. It is however well known that maximal CH2O underestimates distal NaCl reabsorption because a substantial fraction of generated free water disappears by back diffusion (BD), even in the absence of ADH (1). Bartoli cs (2) have proposed to analyze tubular functions and BD using the effects of furosemide (F) based on the assumption that F: a) completely blocks NaCl reabsorption in the Loop of Henle, but not elsewhere, b) completely abolishes osmotic gradients in the medulla, and thus eliminates BD. Consequently, maximal urine flow during F measures distal delivery, and the fact that without F less urine is produced is due to BD. The proximal reabsorption (Rprox) can be calculated from distal delivery and filtration rate
KeywordsProximal Tubule Distal Tubule Back Diffusion Maximal Urine Flow Lithium Clearance
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- 1.Roy, D.R., and Jamison, R.J. Ch. 38 The Kidney. Raven press N.Y. 1985.Google Scholar