Henle’s Loop (HL) Reabsorption Measured by Furosemide (F)
We have developed (1) and extensively applied (1,4) a new method to measure transport by each segment of the human nephron. We assumed that F, by abolishing NaCl transport of HL, wipes out the osmotic gradient between collecting duct (CD) urine and interstitium, and the abstraction of solute free water (SFW) that occurs in the absence of ADH: therefore, the urine flow during maximal water diuresis (MWD) plus F (Vf) represents a true measurement of delivery from proximal tubule (PT). In addition, the urine will be diluted by the distal tubule (DT) during F: therefore, the SFW excreted during F, CH20f, is that formed by the DT, CH20-DT. Thus, CH20f = CH20-DT (I). The difference between V during F (Vf) and that during MWD alone (V) measures the volume of SFW reabsorbed in the absence of ADH, indicated as CH20-BD. This being the part of SFW which is not excreted, the true SFW generated is that excreted (CH20) plus that reabsorbed (CH20-BD): hence, CH20-T = CH20-BD + CH20 (II), where CH20-T is the total SFW formed. The SFW generated by HL alone can be calculated as CH20-HL = CH20-T - CH20-DT (III). For these concepts to gain a wide acceptance, it is necessary to confirm the measurements by an independent method. We devised the present experiments to compare by an independent method the results obtained by previously published technique based on MWD.
KeywordsCatheter Beach Sorb Furosemide Inulin
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