Characteristics of Sodium and Water Transport in the Diluting Segment of the Dog Nephrons after Nephrectomy and Ureteroperitoneostomy

Abstract

In 4 dogs, free water clearance (C_H2O) increased with solute excretion during loading with hypotonic saline until an osmolal clearance of 5–6 ml per 100 ml filtrate. C_H2O was similar after ureteroperitoneostomy of one kidney and 3–4 weeks after nephrectomy of the peritoneostomized kidney. C_H2O from a single excreting kidney was significantly higher than C_H2O of each kidney in the control period, in spite of higher osmolal clearances in control experiments. The increase in C_H2O probably reflects an increase in sodium reabsorption in the distal nephron, as two other indices of distal sodium reabsorption—the natriuretic effect of chlorothiazide and maximal reabsorption of solute-free water (T^cC_H2O)—increased per kidney after nephrectomy in studies on 4 other dogs. It is concluded that sodium reabsorption in the diluting segment (including the medullary part of the ascending limb of Henle's loop), and thereby the capacity to excrete free water and reabsorb solute-free water, are increased after nephrectomy and ureteroperitoneostomy. This increased capacity is not simply a consequence of increased delivery of solutes from the proximal tubules and is not dependent on tubular hypertrophy and hyperplasia.

Key Words:

• Chlorothiazide
• diuresis
• glomerular filtration rate
• natriuresis
• nephrectomy
• sodium
• ureteroperitoneostomy
• urine
• water-electrolyte balance