Effect of changes in renal perfusion pressure on the suppression of proximal tubular sodium reabsorption due to saline loading

A B S T R A C T The renal response to chronic depletion of extracellular volume was examined using the techniques of micropuncture. Depletion of salt and water was produced by administration of furosemide to rats maintained on a sodium-free diet. There was a marked fall in body weight, plasma volume, and glomerular filtration rate. The intrinsic reabsorptive capacity of the proximal tubule, measured by the split-droplet technique, was greatly enhanced. The acceleration of proximal fluid reabsorption could not be accounted for by changes in filtration rate, tubular geometry, or aldosterone secretion. The half-time of droplet reabsorption in the distal tubule was not altered by sodium depletion.An increase in the reabsorption of fluid in the proximal tubule, as demonstrated directly in the present experiments, provides an explanation for a variety of clinical phenomena associated with volume depletion. INTRODUCTIONIt is now well established that expansion of the extracellular fluid leads to renal excretion of salt and water in large part through the mechanism of decreased reabsorption in the proximal tubule. It is also well-known that depletion of extracellular volume regularly induces retention of salt and water, but the mechanism is not so precisely established. There is reason to think that, in addition to a fall in glomerular filtration rate, there is an accelerated reabsorption of sodium in the proximal tubules resulting in decreased delivery of filtrate to the distal nephron. Thus far, however, the evidence has been

Section: Discussioncontrasting

confidence: 49%

Accelerated reabsorption in the proximal tubule produced by volume depletion

Weiner¹,

Weinman²,

Kashgarian³

et al. 1971

“…Plasma volumes were determined in 10 BDL and 9 unoperated rats. After inulin and PAH clearances had been determined in the manner described earlier, carefully measured amounts (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) ACi) of radioiodinated ('I) human serum albumin (Abbott Laboratories, North Chicago, Ill.) were injected into the jugular vein. 60 min later, an arterial blood sample was drawn and the activity of 10 /Al of plasma was determined by liquid scintillation techniques, in an Iso/Cap 300 liquid scintillation system, with appropriate quenched standards and the scintillation solution described above.…”

Section: Methodsmentioning

confidence: 99%

“…Three phenomena thought to play a major role in altering the renal excretion of sodium are (a) changes in the glomerular filtration rate, (b) changes in the endogenous secretion of mineralocorticoids (3), and (c) renal hemodynamic adjustments, including disturbances in the intrarenal distribution of blood flow (5,6) and alterations of Starling forces within the peritubular circulation (12)(13)(14)(15). In the past, the possible interrelationship between the effects of these two hemodynamic adjustments has not been emphasized.…”

Section: Introductionmentioning

confidence: 99%

Intrarenal mechanisms of salt retention after bile duct ligation in rats.

Yarger¹,

Schrader²,

Boyd³

1976

A B S T R A C T In order to study renal salt-retaining mechanisms during the early stages of ascites formation, rats were subjected to bile duct ligation. After this procedure, plasma volumes were found to be reduced and hematocrits slightly increased. The whole-kidney glomerular filtration rate and plasma flows were reduced to 59 and 57% of control values, but the filtration fraction was unchanged. Absolute sodium excretion, as well as the fraction of the filtered sodium load excreted, was also significantly reduced.When micropuncture techniques were used to examine the function of single superficial nephrons, the glomerular filtration rate in these nephrons was found to be reduced to 70% of controlled values, and fractional reabsorption was found to be increased at all accessible sites along the nephron. Filtration by intermediate and juxtamedullary nephrons, determined by Hanssen's technique, was reduced to 55 and 48% of control values.By the use of radioactive microspheres, it was demonstrated that blood flow to superficial, intermediate, and juxtamedullary nephrons was reduced to 49, 59, and 73% of control values. Filtration by superficial nephrons decreased much more than plasma flow-a finding which suggests that the measured increase in fractional reabsorption was associated with an increase in the superficial nephron filtration fraction.From this study, it appears that two factors play an important part in the sodium retention observed in the initial stages of ascites formation following bile duct ligation in rats: (a) a decrease in the filtered sodium Several parts of this manuscript have previously appeared in abstract form (Clin. Res. 22: 52A and 551A) and were presented to the Southern Sectional Meeting of the Ameri-

“…The role of intrarenal hemodynamics or renal interstitial pressure or volume in the control of sodium excretion has received a great deal of attention recently (14)(15)(16)(17)(18). It would appear that even if there is a natriuretic hormone, other factors must be operative in the regulation of tubular sodium transport and that sodium transport in the proximal tubule is under different control than that in the distal tubule (15,16,19).…”

Section: Methodsmentioning

confidence: 99%

Increased sodium reabsorption in the proximal and distal tubule of caval dogs

Kaloyanides¹,

Cacciaguida²,

Pablo³

et al. 1969

A B S T R A C T The effects of water diuresis, hypotonic NaCi, and hypotonic mannitol diuresis on renal sodium and water excretion were examined in normal dogs and in dogs with chronic constriction of the thoracic inferior vena cava and ascites (caval dogs). During all three diuretic states, the capacity to excrete solute-free water relative to the supply of sodium to the water clearing segment of the nephron was significantly greater in the caval dog. This finding was most evident during hypotonic NaCl diuresis but was also striking during hypotonic mannitol diuresis despite the more unfavorable gradient for sodium reabsorption at the distal tubule produced by this agent in caval dogs. In addition, fractional distal sodium load was significantly smaller in caval dogs during water diuresis and could not be increased as readily as in normal dogs by hypotonic NaCl or mannitol infusion. The data indicate that fractional sodium reabsorption is increased at the water clearing segment and the proximal tubule in caval dogs.