Micropuncture study of effects of urea infusion in tubular reabsorption in the rat

A B S T R A C T Proximal and distal tubule micropuncture studies were performed to examine the response to graded extracellular volume (ECV) expansion in 10 normal dogs (stage I), 11 dogs with a unilateral remnant kidney (stage II), and 7 dogs with a remnant kidney after removal of the contralateral kidney (stage III). Before ECV expansion in stage III, there was a suggestive reduction in proximal tubule as well as loop fractional reabsorption of sodium. After ECV expansion to 3% body weight proximal tubule reabsorption was depressed in all groups of animals, while little further inhibition was observed in this segment with additional expansion to 10% body weight. In contrast, the fraction of filtered sodium remaining in the distal tubule rose progressively in all three groups after graded ECV expansion, suggesting that the graded natriuretic response found in the final urine was largely due to a similar response in the loop of Henle rather than that in the proximal tubule. The distal tubule response of the remnant kidney in both stages II and III was greater than that in stage I. These data indicate that although enhanced sodium excretion per nephron in chronic renal failure may be related to uremia, its exaggerated response to ECV expansion is due, at least in part, to cer-

Section: Discussionmentioning

confidence: 96%

Micropuncture Studies of Sodium Tranport in the Remnant Kidney of the Dog THE EFFECT OF GRADED VOLUME EXPANSION

Wen¹,

Wong²,

Evanson³

et al. 1973

“…In contrast to the result with Ringer perfusion, increases in loop perfusion rate were not followed by decreases in SFP when the perfusion fluid contained either the diuretic agents furosemide and triflocin or cyanide or poly-L-lysine. The ascending limb of Henle's loop is considered to be the major site of action of furosemide (14-16) and of triflocin (17)(18)(19). An action in the ascending limb has also been attributed to cyanide (20)(21), however, its action and that of poly-L-lysine are probably not limited to this nephron segment.…”

Section: Methodsmentioning

confidence: 99%

Interference with Feedback Control of Glomerular Filtration Rate by Furosemide, Triflocin, and Cyanide

Wright¹,

Schnermann²

1974

240

110

“…urea load (300 mg/ml at 0.1 ml/min for 20 min) was administered in order to elevate the plasma urea level without expanding body fluids by more than 1% (13). Two additional 30-45 min urine collections were then obtained.…”

Section: Methodsmentioning

confidence: 99%

A Micropuncture Study of Postobstructive Diuresis in the Rat

Yarger¹,

Aynedjian²,

Bank³

1972

100

A B S T R A C T In order to investigate the syndrome of postobstructive diuresis, clearance and micropuncture studies were carried out in rats after relief of 24 hr of bilateral (BUL) or unilateral (UUL) ureteral ligation. In rats with BUL, a striking diuresis and natriuresis occurred when the obstruction to one kidney (the experimental kidney) was relieved. The results were not influenced by administration of vasopressin or d-aldosterone. Whole kidney clearances of inulin and p-aminohippuric acid (PAH) in the experimental kidney were reduced to 10% and 20% of normal, respectively. Superficial nephron inulin and PAH clearances were also reduced, but only to 40% and 45%, respectively. These findings suggest a heterogeneity of nephron function in which deep nephrons were functioning poorly or not at all. To investigate the site of impaired tubular reabsorption in the surface nephrons, absolute and fractional water reabsorption was measured. Absolute reabsorption was found to be decreased all along the nephron. Fractional reabsorption in proximal tubules was normal, as indicated *by an average endproximal tubular fluid per plasma inulin (TF/Pi.) of 2.16 vs. 2.30 in controls. TF/Pri was markedly decreased in distal tubules (2.91 vs. 8.02) and final urine (5.56 vs. 263). These observations indicate that the major sites of impaired sodium reabsorption leading to the diuresis were beyond the proximal tubule.