A Study in Vivo of Peritubular Oncotic Pressure and Proximal Tubular Reabsorption in the Rat

1976 ◽  
Vol 51 (4) ◽  
pp. 379-392 ◽  
Author(s):  
J. D. Conger ◽  
E. Bartoli ◽  
L. E. Earley
Keyword(s):  
Tubular Reabsorption ◽  
Detectable Effect ◽  
Oncotic Pressure ◽  
Peritubular Capillary ◽  
Fluid Reabsorption ◽  
Proximal Tubular ◽  
Convoluted Tubules ◽  
Proximal Tubular Reabsorption ◽  
Tubule Fluid

1. Peritubular capillary microperfusion was used to examine the effects of protein-free and hyperoncotic homologous plasma on fluid reabsorption by proximal convoluted tubules in the hydropenic rat. 3H-labelled p-aminohippurate was added to perfusates for the purpose of estimating the extent to which tubules under study were bathed by the perfusates. [14C]Mannitol was added to perfusates in order to detect contamination of collected tubular fluid by perfusates. 2. Hydrostatic pressures were monitored in the peritubular microvasculature and adjacent proximal tubules during perfusion. Evidence for secretion of p-aminohippurate from perfusate into tubules under study was determined by collecting tubular fluid from both early and late puncture sites. Fractional and absolute reabsorption were not affected by either the protein-free or the hyperoncotic plasma. 3. When acetazolamide was added to the perfusate both fractional and absolute reabsorptive rates decreased by an average of 36%, indicating that the techniques were capable of detecting a decrease in proximal tubular reabsorption. 4. It is concluded that under the conditions of this study changes in peritubular capillary protein concentrations have no detectable effect on the rate of proximal convoluted tubule fluid reabsorption.

Determinants of proximal tubular reabsorption as mechanisms of glomerulotubular balance

1978 ◽  
Vol 235 (2) ◽  
pp. F142-F150 ◽  
Author(s):  
B. J. Tucker ◽  
R. C. Blantz
Keyword(s):  
Proximal Tubule ◽  
Filtration Rate ◽  
Oncotic Pressure ◽  
Peritubular Capillary ◽  
Nephron Filtration Rate ◽  
Vein Occlusion ◽  
Proximal Tubular ◽  
Range Of Values ◽  
Proximal Tubular Reabsorption ◽  
Glomerulotubular Balance

The determinants of absolute proximal reabsorption (APR) were studied in four groups of rats during hydropenia, partial renal vein occlusion (RVO), saline expansion, and RVO after saline expansion. Nephron filtration rate (SNGFR), nephron plasma flow (RPF), APR, and proximal tubule (Pt) peritubular capillary (HPc), and interstitial (HPi) hydrostatic pressures were measured by micropuncture techniques. Subcapsular space (pii) and star peritubular capillary (piE) oncotic pressures were also determined. The peritubular capillary permeability coefficiency (LpAR) and the corresponding effective reabsorptive pressure (ERP) were computed, where APR = LpAR . ERP, and ERP = net reabsorptive pressure across the peritubular capillary. The results indicate that APR correlates best with SNGFR (P less than 0.05), but not with (pii - HPi), RPF, or LpAR. There was a significant relationship between piE and LpAR, where LpAR fell with increases in piE (P less than 0.01). In conclusion, 1) changes in absolute proximal reabsorption correlate best with changes in nephron filtration rate but not with (pii - HPi) across this range of values, 2) changes in efferent oncotic pressure (piiE) correlated inversely with LpAR, and 3) glomerulotubular balance in the proximal tubule can be partially attributed to intraluminal factors.

Flash photolysis of caged nitric oxide inhibits proximal tubular fluid reabsorption in free-flow nephron

2005 ◽  
Vol 289 (2) ◽  
pp. R620-R626 ◽  
Author(s):  
Kay-Pong Yip
Keyword(s):  
Nitric Oxide ◽  
Proximal Tubule ◽  
Flash Photolysis ◽  
Tubular Reabsorption ◽  
Fluid Reabsorption ◽  
Proximal Tubular ◽  
Tubular Flow ◽  
Tubular Fluid Reabsorption ◽  
Reabsorption Rate ◽  
Proximal Tubular Reabsorption

A nonobstructing optical method was developed to measure proximal tubular fluid reabsorption in rat nephron at 0.25 Hz. The effects of uncaging luminal nitric oxide (NO) on proximal tubular reabsorption were investigated with this method. Proximal fluid reabsorption rate was calculated as the difference of tubular flow measured simultaneously at two locations (0.8–1.8 mm apart) along a convoluted proximal tubule. Tubular flow was estimated on the basis of the propagating velocity of fluorescent dextran pulses in the lumen. Changes in local tubular flow induced by intratubular perfusion were detected simultaneously along the proximal tubule, indicating that local tubular flow can be monitored in multiple sites along a tubule. The estimated tubular reabsorption rate was 5.52 ± 0.38 nl·min−1·mm−1 ( n = 20). Flash photolysis of luminal caged NO (potassium nitrosylpentachlororuthenate) was induced with a 30-Hz UV nitrogen-pulsed laser. Release of NO from caged NO into the proximal tubule was confirmed by monitoring intracellular NO concentration using a cell-permeant NO-sensitive fluorescent dye (DAF-FM). Emission of DAF-FM was proportional to the number of laser pulses used for uncaging. Photolysis of luminal caged NO induced a dose-dependent inhibition of proximal tubular reabsorption without activating tubuloglomerular feedback, whereas uncaging of intracellular cGMP in the proximal tubule decreased tubular flow. Coupling of this novel method to measure reabsorption with photolysis of caged signaling molecules provides a new paradigm to study tubular reabsorption with ambient tubular flow.

Superficial nephron responses to peritubular capillary infusions of angiotensins I and II

1987 ◽  
Vol 252 (5) ◽  
pp. F818-F824 ◽  
Author(s):  
K. D. Mitchell ◽  
L. G. Navar
Keyword(s):  
Enzyme Inhibitor ◽  
Isotonic Saline ◽  
Tubular Reabsorption ◽  
Ang Ii ◽  
Peritubular Capillary ◽  
Single Nephron ◽  
Proximal Tubular ◽  
Flow Pressure ◽  
Proximal Tubular Reabsorption ◽  
Stop Flow

Proximal tubular reabsorption, stop-flow pressure (SFP), and single nephron glomerular filtration rate (SNGFR) were measured in the absence of and during infusion of an isotonic saline solution containing either angiotensin I (ANG I; 10(-6) to 10(-5) M) or angiotensin II (ANG II; 10(-9) to 10(-7) M) into an adjacent peritubular capillary at a rate of 20 nl/min. Dilution of the infused ANG I and ANG II occurred in the peritubular capillary blood and as the peptides diffused into the interstitium. Infusion of either 10(-7) M ANG II or 10(-5) M ANG I increased proximal fractional fluid reabsorption (FRH2O) and decreased both SFP and SNGFR. There were no significant changes in FRH2O or SNGFR during infusion of 10(-5) M ANG I when the converting enzyme inhibitor enalaprilat (MK 422, 10(-3) M) was added to the infusate. Similarly, peritubular infusion at lower concentrations of either ANG II (10(-9) or 10(-8) M) or ANG I (10(-6) M) did not alter FRH2O, SFP, or SNGFR. These data indicate that conversion of ANG I to ANG II can occur in the peritubular capillary or interstitial environment and that increases above the normal endogenous levels in the postglomerular interstitial ANG II concentration can enhance proximal tubular reabsorption and increase preglomerular resistance and thereby reduce SNGFR.

A Micropuncture Study of Proximal Tubular Function after Acute Hydrochlorothiazide Administration to Brattleboro Rats with Diabetes Insipidus

1979 ◽  
Vol 57 (5) ◽  
pp. 427-434 ◽  
Author(s):  
S. J. Walter ◽  
J. F. Laycock ◽  
D. G. Shirley
Keyword(s):  
Glomerular Filtration Rate ◽  
Diabetes Insipidus ◽  
Glomerular Filtration ◽  
Filtration Rate ◽  
Inhibitory Effect ◽  
Tubular Reabsorption ◽  
Brattleboro Rats ◽  
Fluid Reabsorption ◽  
Proximal Tubular ◽  
Proximal Tubular Reabsorption

1. Renal function in anaesthetized Brattleboro rats with hereditary hypothalamic diabetes insipidus was studied with micropuncture techniques before, and 1–3 h after, a single injection of hydrochlorothiazide. 2. In rats given hydrochlorothiazide and kept in sodium and water balance, total glomerular filtration rate and superficial nephron filtration rate were similar to values in control animals, whereas fractional fluid reabsorption in the proximal tubule (as evidenced by tubular fluid/plasma inulin concentration ratios) was slightly, but significantly, reduced. This suggests that hydrochlorothiazide may have a small direct inhibitory effect on proximal tubular reabsorption. 3. When rats were given hydrochlorothiazide and the resultant extra urinary sodium losses were not replaced, there was a marked antidiuresis. In these animals total glomerular filtration rate was reduced by 23% and superficial nephron filtration rate by 27% when compared with values in control rats. Fractional proximal tubular fluid reabsorption increased significantly whereas absolute proximal fluid reabsorption was unaffected. 4. It is concluded that the reduction in body sodium which follows acute hydrochlorothiazide administration over-rides any inhibitory effect of the drug on proximal tubular reabsorption, and leads instead to an increase in fractional fluid reabsorption at this site. This effect, combined with the fall in glomerular filtration rate, results in a greatly reduced delivery of fluid to the more distal nephron segments, and is probably largely responsible for the observed antidiuresis.

Renal tubular uptake of protein: effect of molecular charge

1983 ◽  
Vol 244 (4) ◽  
pp. F436-F441 ◽  
Author(s):  
E. I. Christensen ◽  
H. G. Rennke ◽  
F. A. Carone
Keyword(s):  
Cytochrome C ◽  
Proximal Tubule ◽  
Isoelectric Point ◽  
Tubular Reabsorption ◽  
Molecular Configuration ◽  
Molecular Charge ◽  
Proximal Tubular ◽  
The Difference ◽  
Proximal Tubular Reabsorption

The effect of molecular charge of proteins on proximal tubular reabsorption was evaluated in the rat. Native and two cationized forms of albumin, native and anionized lysozyme, and native and anionized cytochrome c were iodinated with 125I. The different forms of each type of protein were alternately microinfused into the same site of proximal convoluted tubules in vivo. Tubular reabsorption was determined as the difference between the amounts of TCA-precipitable radioactivity infused and recovered in the urine. At low concentration of albumin 5 times more cationized than anionic albumin and 2.7 times more cationic than anionized lysozyme were reabsorbed by the proximal tubule. At two of four concentrations, proximal tubular uptake of cationic cytochrome c exceeded that of anionized cytochrome c. Uptake of cationic cytochrome c exceeded that of cationic lysozyme; however, the difference in uptake between native cationic and anionized species of the two proteins was much greater for lysozyme than for cytochrome c. The data reveal that a higher isoelectric point significantly enhances proximal tubular reabsorption of albumin, lysozyme, and cytochrome c and that proteins with similar molecular weight and isoelectric point are not necessarily reabsorbed to the same degree. This suggests that in addition to total molecular charge the molecular configuration and/or distribution of electrical charges on teh protein surface determine protein binding by the luminal membrane and subsequent endocytosis by the proximal tubule.

Can causality be determined from proximal tubular reabsorption and peritubular physical factors?

1986 ◽  
Vol 250 (1) ◽  
pp. F169-F175 ◽  
Author(s):  
B. J. Tucker ◽  
C. A. Mundy ◽  
R. C. Blantz
Keyword(s):  
Steady State ◽  
Epithelial Transport ◽  
Capillary Flow ◽  
Tubular Reabsorption ◽  
Physical Factors ◽  
Peritubular Capillary ◽  
Fluid Uptake ◽  
Before And After ◽  
Proximal Tubular ◽  
Proximal Tubular Reabsorption

Many studies in the literature have drawn conclusions regarding the mechanism of change in absolute proximal tubular reabsorption (APR) based on steady-state measurements of proximal reabsorptive rates and the peritubular capillary. The proximal reabsorptive rate, APR, is the product of the effective reabsorptive pressure (ERP) and the peritubular capillary reabsorptive coefficient (LpAR) (APR = ERP . LpAR). The ERP is defined by the net hydrostatic and oncotic pressure gradient acting across the capillary wall from interstitium to peritubular capillary flow. The relationship APR = ERP . LpAR is predefined, and steady-state measurements do not permit determination of causality because primary changes in any variable obligate a proportional change in a second variable. As an example of the difficulties in interpretation of this type of analysis, we have examined the APR and factors contributing to ERP and LpAR before and after the administration of benzolamide, a carbonic anhydrase inhibitor, to saline-expanded Munich-Wistar rats. Alterations in peritubular capillary fluid uptake cannot always be interpreted as casual mechanisms for changes in absolute fluid reabsorption but may result from primary alterations in epithelial transport.

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