Studies on Glomerulotubular Balance During Aortic Constriction, Ureteral Obstruction and Venous Occlusion in Hydropenic and Saline-Loaded Rats

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A B S T R A C T Free-flow and stop-flow intratubular pressures were measured in rats with an improved Gertz technique using Landis micropipets or a Kulite microtransducer. In hydropenia, average single nephron glomerular filtration rate was 29.3 nl/min, glomerular hydrostatic pressure (stop-flow pressure + plasma colloid osmotic pressure) was 70 cm H20 and mean glomerular effective filtration pressure was 12.7-14.3 cm H20, approaching zero at the efferent end of the glomerulus. Thus, the glomerulus is extremely permeable, having a filtration coefficient four to five times greater than previously estimated. Mean effective filtration pressure and single nephron glomerular filtartion rate fell with elevated ureteral pressure and rose with volume expansion, more or less proportionately. Changes in effective filtration pressure were due primarily to increased intratubular pressure in ureteral obstruction and to reduced plasma colloid osmotic pressure in volume expansion; glomerular hydrostatic pressure remained constant in both conditions and thus played no role in regulation of filtration rate.

Section: Results Are Summarized Inmentioning

confidence: 99%

Effective glomerular filtration pressure and single nephron filtration rate during hydropenia, elevated ureteral pressure, and acute volume expansion with isotonic saline

Andreucci¹,

Herrera-Acosta²,

Rector³

et al. 1971

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“…It seems unlikely that this relationship could be due to an effect of tubular distension on reabsorption as suggested by Gertz et al (4). It has been shown that during obstruction of individual tubules (12,27), as well as during partial ureteral obstruction (6,7), reabsorption fell at a time when tubular diameter was increased. We have made similar observations in this laboratory.3 Also, it seems unlikely that the coupling of load and reabsorption is mediated by an effect of delivery out of the proximal tubule to activate a feedback mechanism such as suggested by Leyssac (2).…”

Section: Details Of This Experiments Are Given Inmentioning

confidence: 91%

“…However, this concept cannot account for the presence of glomerulotubular balance when filtration rate is lowered by ureteral or renal venous obstruction which produce tubular distension at a time when reabsorption is decreased (6,7). Each of the above explanations for glomerulotubular balance involves some intraluminal effect of changes in the delivery of filtrate to bring about concordant changes in the rate of reabsorption.…”

Section: Introductionmentioning

confidence: 99%

Effect of Intraluminal Flow on Proximal Tubular Reabsorption

Bartoli¹,

Conger²,

Earley³

1973

A B S T R A C T Micropuncture techniques in the rat were used to reinvestigate the possibility that intraluminal flow rate per se may influence net volume reabsorption by the proximal tubule. An experimental design was devised which lowered intraluminal flow without affecting filtration rate of the nephron under study or without directly affecting other renal hemodynamics. In 11 rats flow of tubular fluid between early and late proximal tubular sites was reduced by partially collecting tubular fluid at the early puncture site. In 42 nephrons the rate of flow of tubular fluid was reduced an average of 45% without changing nephron filtration rate and there was an associated reduction in reabsorption between the two sites which averaged 29%. This indicated 63% balance between delivery of tubular fluid and the rate of reabsorption between two sites along proximal tubules. The results of these studies indicate that a reduction in delivery of normal filtrate along the proximal tubule is associated with a concordant reduction in the absolute rate of reabsorption. Since this relationship occurred in the absence of changes in renal hemodynamics or even a change in filtration rate of the nephron under study it is concluded that changes in intraluminal load per se play an important role in the phenomenon of glomerulotubular balance.

“…In the normal rat, there is a considerable body of evidence which indicates that the proximal tubule is endowed with little intrinsic capacity for regulation of sodium and water reabsorption (34)(35)(36)(37)(38)(39)(40)(41)(42)(43) and that the control of APR is governed primarily by alterations in the peritubular transcapillary Starling forces (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)28). The data obtained in the present study indicate that APR in rats with a moderate degree of NSN is likewise governed largely by the peritubular environment, and in particular, by the extent to which 7rE is reduced.…”

Section: Control Glomerulonephrltismentioning

confidence: 99%

Control of proximal tubule fluid reabsorption in experimental glomerulonephritis.

Maddox¹,

Bennett²,

Deen³

et al. 1975

A B S T R A C r We have recently shown that in the early autologous phase of nephrotoxic serum nephritis (NSN) single nephron glomerular filtration rate is unchanged from values in normal hydropenic control rats, but that single nephron filtration fraction and efferent arteriolar oncotic pressure (7rE) are reduced because of a mi rked reduction in the glomerular capillary ultrafiltration coefficient. The present study was undertaken to examine the influence of this decline in 7rE as well as the other known determinants of peritubular capillary fluid exchange on absolute proximal fluid reabsorption (APR) in NSN. The findings indicate that APR and proximal fractional reabsorption are reduced significantly in NSN, relative to values in a separate group of age and weight-matched normal hydropenic control rats studied concurrently. In addition to the measured decline in 7rE, efferent arteriolar plasma flow (QE) and peritubular capillary hydraulic pressure (Pc) were found to increase significantly, while interstitial oncotic pressure. estimated from hilar lymph, was not significantly different from values in control rats. Using a mathematical model of peritubular capillary fluid uptake we found that, assuming that the capillary permeability-surface area product and interstitial hydraulic Portions of these studies were presented at the 7th Annual Meeting of the