The Effect of Oncotic Pressure Changes in Peritubular Capillaries on Fluid Reabsorption by Proximal Tubules of Rat Kidneys1

2015 ◽  
pp. 17-25 ◽  
Author(s):  
E. E. Windhager ◽  
A. Spitzer
Keyword(s):  
Proximal Tubules ◽  
Oncotic Pressure ◽  
Fluid Reabsorption ◽  
Peritubular Capillaries ◽  
Pressure Changes

Passive driving forces of proximal tubular fluid and bicarbonate transport: gradient dependence of H+ secretion

1983 ◽  
Vol 245 (5) ◽  
pp. F622-F633 ◽  
Author(s):  
Y. L. Chan ◽  
G. Malnic ◽  
G. Giebisch
Keyword(s):  
Driving Forces ◽  
Potential Gradient ◽  
Glass Electrode ◽  
Bicarbonate Transport ◽  
Oncotic Pressure ◽  
Luminal Membrane ◽  
Peritubular Capillaries ◽  
Proximal Tubular ◽  
Luminal Flow ◽  
Pressure Changes

The effect of oncotic pressure changes on fluid (Jv) and net bicarbonate transport (JHCO-3) and the transepithelial bicarbonate permeability (PHCO-3) were measured by an improved luminal and capillary microperfusion method that allows paired experiments on the same tubule. Rat proximal tubules were pump-perfused and Jv and [HCO-3] measured with [14C]inulin and a pH glass electrode. Raising peritubular protein (0-8-15 g/100 ml bovine serum albumin) stimulated Jv and HCO-3 reabsorption. The response to oncotic pressure changes was asymmetrical since changes of the luminal protein concentration had no significant effects. Whereas transepithelial solvent drag effects on HCO-3 must be minimal, peritubular protein most likely stimulates translocation of fluid and bicarbonate from intercellular spaces into peritubular capillaries. PHCO-3 was measured from HCO-3 net flux along a lumen-to-capillary-directed electrochemical potential gradient. In these experiments active H+ transport and Jv were minimized by 10(-4) M acetazolamide and luminal raffinose. PHCO-3 was 1.77 X 10(-5) cm X s-1 and was unaffected by increasing luminal flow rate from 10 to 45 nl X min-1. Since bicarbonate backflux is only a small fraction of physiological rates of JHCO-3, net transport alterations at varying [HCO-3] in the lumen must be due to changes in active HCO-3 (H+) transport. Thus, active H+ ion secretion across the luminal membrane of the proximal tubule is gradient dependent.

Osmotic forces driving water reabsorption in the proximal tubule of the rat kidney

1989 ◽  
Vol 257 (4) ◽  
pp. F669-F675 ◽  
Author(s):  
R. Green ◽  
G. Giebisch
Keyword(s):  
Reflection Coefficient ◽  
Water Permeability ◽  
Rat Kidney ◽  
Proximal Tubules ◽  
Osmotic Gradient ◽  
Water Reabsorption ◽  
Fluid Flux ◽  
Fluid Reabsorption ◽  
Ionic Fluxes ◽  
Peritubular Capillaries

Simultaneous microperfusion of proximal tubules and peritubular capillaries in kidneys of rats anesthetized with Inactin was used to measure reabsorption of fluid in response to an imposed osmotic gradient. The tubular fluid was isotonic and the peritubular capillaries were made hypertonic with NaCl or NaHCO3. Mean gradients and ionic fluxes were measured. When no gradient was imposed tubular fluid became hypotonic and rate of fluid reabsorption was 0.700 nl.mm-1.min-1. Imposition of a 25 mM NaCl gradient increased fluid flux to 3.887 nl.mm-1.min-1, whereas 25 mM NaHCO3 stimulated 5.226 ml/mm fluid reabsorption. This gave a relative reflection coefficient of NaCl:NaHCO3 of 0.73. Apparent water permeability varied with highest values for the smallest gradients. This suggests the possibility of a compartment in the epithelium that is hypertonic to the peritubular capillaries. The hypertonicity required to account for fluid movement was 6-16 mosmol/kg.

Luminal hypotonicity: a driving force for fluid absorption from the proximal tubule

1984 ◽  
Vol 246 (2) ◽  
pp. F167-F174 ◽  
Author(s):  
R. Green ◽  
G. Giebisch
Keyword(s):  
Reflection Coefficient ◽  
Driving Force ◽  
Proximal Tubules ◽  
Tubular Epithelium ◽  
Fluid Absorption ◽  
Fluid Reabsorption ◽  
Hypotonic Fluid ◽  
Peritubular Capillaries ◽  
Proximal Tubular ◽  
Proximal Tubular Epithelium

The ability of rat proximal tubules to generate a hypotonic luminal fluid was investigated. Simultaneous perfusion of tubules and peritubular capillaries was performed with simple solutions. When tubules were perfused at 10 nl X min-1 and NaCl was the perfusate for tubules and capillaries, solute and fluid (0.41 nl X min-1 X mm-1) were transported and the luminal fluid became hypotonic (delta osmol = -1.7 mosmol X kg-1). When the same solutions were used but the tubule was perfused at 45 nl X min-1, more fluid (0.89 nl X min-1 X mm-1) was reabsorbed and the fluid became more hypotonic (delta osmol = -3.9 mosmol X kg-1). Bicarbonate in the peritubular capillaries increased the fluid reabsorption (1.21 nl X min-1 X mm-1) but did not generate cryoscopically hypotonic fluid. Cyanide abolished all net movement of fluid and solute. It is concluded that the tubule can generate a hypotonic fluid, that the hydraulic conductivity for proximal tubular epithelium is 3,200-3,400 microns X s-1, and that the reflection coefficient for NaHCO3 is slightly higher than for NaCl.

Colloid osmotic pressure changes in isolated isogravimetric cat hindlimb

1982 ◽  
Vol 242 (4) ◽  
pp. H512-H519 ◽  
Author(s):  
P. D. Watson
Keyword(s):  
Osmotic Pressure ◽  
Maximum Rate ◽  
Venous Pressure ◽  
Colloid Osmotic Pressure ◽  
Oncotic Pressure ◽  
Weight Changes ◽  
Constant Weight ◽  
Fluid Reabsorption ◽  
Capillary Filtration Coefficient ◽  
Pressure Changes

The development of osmotic pressure, following the addition of bovine serum albumin (BSA) to the perfusate, was measured in an isogravimetric cat hindlimb fully dilated with papaverine. The changes in colloid osmotic pressure were followed by recording the changes in venous pressure (PVI) necessary to maintain constant weight. Capillary filtration coefficient (CFC) and vascular compliances were calculated from weight changes following steps in venous pressure. Venous BSA levels reached arterial within 1 min, and PVI reached a new steady state 13.1 +/- 0.9 (SE) min (n = 9 in 6 limbs) after adding BSA. This apparent delay in the development of the osmotic pressure agrees with earlier reports. However, when the BSA was added under constant venous pressure conditions, the fluid reabsorption reached its maximum rate within 1.5 min. The data suggest that the BSA is osmotically fully effective after the capillary washin. The slowness of the rise of PVI in the isogravimetric state is probably caused by the time necessary to absorb sufficient fluid from the interstitium to raise the capillary pressure to a level that balances the increased oncotic pressure. A mathematical model supports this explanation.

Renal cortical interstitium and fluid absorption by peritubular capillaries

1994 ◽  
Vol 266 (2) ◽  
pp. F175-F184 ◽  
Author(s):  
K. Aukland ◽  
R. T. Bogusky ◽  
E. M. Renkin
Keyword(s):  
Rat Kidney ◽  
Colloid Osmotic Pressure ◽  
Capillary Wall ◽  
Peritubular Capillary ◽  
Fluid Reabsorption ◽  
Fluid Uptake ◽  
Peritubular Capillaries ◽  
Capillary Fluid ◽  
Renal Cortical Interstitium ◽  
Relative Retardation

Every minute, the cortical peritubular capillaries in a 1-g rat kidney take up more than 0.5 ml tubular reabsorbate. Studies of renal lymph and measurements of pressure in capillaries (Pc) and interstitium (Pi) indicate that normally the protein colloid osmotic pressure of peritubular capillary plasma (COPp) provides the necessary absorptive force, keeping Pi at 2-4 mmHg, i.e., 8-10 mmHg lower than Pc. At reduced COPp, continued delivery of fluid from the tubules automatically raises Pi to maintain capillary fluid uptake. The transient Pi response to sudden exposure of the kidney to subatmospheric pressure shows that such adjustment of forces may take place in only 5 s. Most remarkable, adjustment of forces may take place in only 5 s. Most remarkable, reabsorption continues during protein-free perfusion of the isolated rat kidney, apparently effected by a Pi exceeding Pc. A relative retardation of interstitial uptake of ferritin from plasma in this case suggests fluid reabsorption through both small and large pores in the capillary wall. Collapse of the capillaries is presumably prevented by tight tethering to the capillary wall, giving the narrow interstitium a very low compliance.

Return of the secretory kidney

2002 ◽  
Vol 282 (1) ◽  
pp. F1-F9 ◽  
Author(s):  
Jared J. Grantham ◽  
Darren P. Wallace
Keyword(s):  
Glomerular Filtration ◽  
Extracellular Fluid ◽  
Fluid Secretion ◽  
Proximal Tubules ◽  
Renal Tubules ◽  
Functional Elements ◽  
Dry Land ◽  
Fluid Reabsorption ◽  
Collecting Ducts ◽  
Urine Formation

The evolution of the kidney has had a major role in the emigration of vertebrates from the sea onto dry land. The mammalian kidney has conserved to a remarkable extent many of the molecular and functional elements of primordial apocrine kidneys that regulate fluid balance and eliminate potentially toxic endogenous and xenobiotic molecules in the urine entirely by transepithelial secretion. However, these occult secretory processes in the proximal tubules and collecting ducts of mammalian kidneys have remained underappreciated in the last half of the twentieth century as investigators focused, to a large extent, on the mechanisms of glomerular filtration and tubule sodium chloride and fluid reabsorption. On the basis of evidence reviewed in this paper, we propose that transepithelial salt and fluid secretion mechanisms enable mammalian renal tubules to finely regulate extracellular fluid volume and composition day to day and maintain urine formation during the cessation of glomerular filtration.

scholarly journals Influence of serum proteins on net fluid reabsorption of isolated proximal tubules

1972 ◽  
Vol 2 (2) ◽  
pp. 66-75 ◽  
Author(s):  
Jared J. Grantham ◽  
Patti B. Qualizza ◽  
Larry W. Welling
Keyword(s):  
Serum Proteins ◽  
Proximal Tubules ◽  
Fluid Reabsorption

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.

Sign in / Sign up

Export Citation Format

Share Document