Balance between tubular flow rate and net fluid reabsorption in the proximal convolution of the rat kidney

1968 ◽  
Vol 304 (1) ◽  
pp. 90-103 ◽  
Author(s):  
J. Schnermann ◽  
M. Wahl ◽  
G. Liebau ◽  
H. Fischbach
Keyword(s):  
Flow Rate ◽  
Rat Kidney ◽  
Fluid Reabsorption ◽  
Tubular Flow ◽  
Proximal Convolution

Role of luminal hydrostatic pressure in proximal tubular fluid reabsorption in the rat

1975 ◽  
Vol 229 (3) ◽  
pp. 813-819 ◽  
Author(s):  
A Grandchamp ◽  
Scherrer ◽  
D Scholer ◽  
J Bornand
Keyword(s):  
Hydrostatic Pressure ◽  
Proximal Tubule ◽  
Pressure Difference ◽  
Unit Area ◽  
Rat Kidney ◽  
Fluid Reabsorption ◽  
Proximal Tubular ◽  
Tubular Fluid Reabsorption ◽  
Selective Change

The effect of small changes in intraluminal hydrostatic pressure (P) on the tubular radius (r) and the net fluid reabsorption per unit of surface area of the tubular wall (Js) has been studied in the proximal tubule of the rat kidney. The split-drop method was used to simultaneously determine Js and r. Two standardized split-drop techniques A and B allow selective change in P. P was 31.6 +/- 1.3 mmHg in technique A and 15.5 +/- 1.5 in technique B. The pressure difference significantly affected the tubular radius; r was 21.9 +/- 0.4 and 18.6 +/- 0.5 mum in the split drop A and B, respectively. In contrast, net transepithelial fluid reabsorption Js was unchanged. Js amounted to 2.72 +/- 0.20, and 2.78 +/- 0.33 10(-5) cm3 cm-2 s-1 in split drop A and B. The absence of variations in Js could result from two opposite effects of pressure. P might enhance Js by increased ultrafiltration. However, the rise in r might decrease the density of the intraepithelial transport paths per unit area of tubular wall and therefore might decrease Js.

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.

Potassium transport in the distal tubule and collecting duct of the rat

1975 ◽  
Vol 229 (5) ◽  
pp. 1403-1409 ◽  
Author(s):  
HJ Reineck ◽  
RW Osgood ◽  
TF Ferris ◽  
JH Stein
Keyword(s):  
Flow Rate ◽  
Collecting Duct ◽  
Distal Tubule ◽  
Potassium Transport ◽  
Distal Convoluted Tubule ◽  
Potassium Excretion ◽  
Flow Rates ◽  
Urinary Potassium ◽  
Potassium Secretion ◽  
Tubular Flow

Because of recent conflicting results, micropuncture studies were performed to clarify the respective role of the distal convoluted tubule and collecting duct in the regulation of urinary potassium excretion. Five groups of Sprague-Dawley rats were studied: group I, hydropenia (n = 10); group II, Ringer loading (n = 7); group III, acute KC1 loading (n = 6); group IV, mannitol diuresis (n = 6); group V, KC1 infusion during mannitol diuresis (n = 7). Early and late distal tubules were identified with intravenous injections of lissamine green. In each animal net secretion of potassium occurred along the distal convoluted tubule, and a direct relationship between distal tubular flow rate and potassium secretion was observed. The magnitude of potassium secretion at high distal tubular flow rates was dependent on the model studied. Potassium transport beyond the distal tubule was evaluated by comparing end distal potassium delivery and fractional potassium excretion. At low urinary flow rates net reabsorption was observed, whereas at higher flow rates no net transport occurred. Thus, flow rate along the collecting duct may be a major determinant of urinary potassium excretion.

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.

Proximal tubular Na, Cl, and HCO3 reabsorption and renal oxygen consumption

1984 ◽  
Vol 247 (1) ◽  
pp. F151-F157 ◽  
Author(s):  
S. W. Weinstein ◽  
R. Klose ◽  
J. Szyjewicz
Keyword(s):  
Oxygen Consumption ◽  
Ion Transport ◽  
Rat Kidney ◽  
Fluid Reabsorption ◽  
Bicarbonate Reabsorption ◽  
Renal Oxygen Consumption ◽  
Proximal Tubular ◽  
Tubular Fluid Reabsorption ◽  
Renal Oxygen

The majority of the oxygen consumed by the rat kidney appears to occur in the proximal tubule. Therefore changes in metabolically linked ion transport in this segment of the nephron should result in changes in renal oxygen consumption. To study the role of bicarbonate reabsorption in metabolically linked proximal tubular ion transport a series of micropuncture-clearance-extraction experiments were performed comparing the effects of the carbonic anhydrase inhibitor benzolamide and of hypertonic sodium bicarbonate infusion with control conditions in the rat. End-proximal tubular fluid and chloride reabsorption were measured. From these, the rates of sodium and bicarbonate reabsorption were estimated. Simultaneously with the tubular fluids, extraction collections were obtained for determination of renal oxygen consumption. Both benzolamide and hypertonic bicarbonate reduced proximal tubular fluid reabsorption while concomitantly reducing the transepithelial gradient for chloride. The mean rate of renal oxygen consumption did not differ from the control rate in either experimental group and could be dissociated from the calculated net rates of proximal tubular sodium, chloride, and bicarbonate reabsorption. We interpret these data as evidence that proximal tubular hydrogen ion secretion supporting bicarbonate reabsorption requires at most small amounts of oxidative energy, less than detectable by these techniques. The data, in contrast, support the conclusion that the chloride-bicarbonate transepithelial gradient appears to be an important passive driving force in vivo for proximal tubular fluid reabsorption.

A closed-loop analysis of the tubuloglomerular feedback mechanism

1991 ◽  
Vol 261 (5) ◽  
pp. F880-F889 ◽  
Author(s):  
N. H. Holstein-Rathlou
Keyword(s):  
Flow Rate ◽  
Closed Loop ◽  
Feedback Mechanism ◽  
Open Loop ◽  
Tubuloglomerular Feedback ◽  
Operating Point ◽  
Sprague Dawley ◽  
Loop Analysis ◽  
Experimental Conditions ◽  
Tubular Flow

The tubuloglomerular feedback (TGF) mechanism is of importance in the regulation of glomerular filtration rate (GFR). A second mechanism of potential importance is the change in proximal pressure caused by a change, for example, in the rate of proximal fluid reabsorption. The quantitative contributions of these two mechanisms to the regulation of GFR and the late proximal flow rate are not known. To determine the regulatory efficiency of these two mechanisms, the late proximal flow rate was perturbed by microperfusion with artificial tubular fluid in halothane-anesthetized Sprague-Dawley rats. The resulting changes in late proximal flow rate were measured by pulse injection of rhodamine dextran. Fluorescence was excited by means of a He-Ne laser. Bolus velocity was measured by videomicroscopy. Tubular pressure was measured by the servonulling method. The microperfusion rate was varied from -15 to 20 nl/min in steps of 5 nl/min. The open-loop gain (OLG) was 3.1 (range 1.5-9.9, n = 13) at the unperturbed tubular flow rate, and decreased as the tubular flow rate was either increased or decreased. The proximal pressure increased by 0.21 +/- 0.03 mmHg per unit increase in late proximal flow rate (nl/min). By use of a mathematical model of the glomerulus, it is estimated that under the present experimental conditions the pressure increase contributes 8% (range 3-15%) of the OLG. It is concluded that, for small perturbations around the operating point, TGF accounts for most of the regulation of GFR and the late proximal flow rate, with changes in the proximal pressure of lesser importance. Furthermore, under closed-loop conditions the operating point for the TGF mechanism is at or close to the point of maximal sensitivity.

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