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  • 1
    Electronic Resource
    Electronic Resource
    Excretion of non-protein-bound cortisol in the rat kidney (1982)
    Springer
    Research in experimental medicine 181 (1982), S. 211-219 
    Details
    ISSN: 1433-8580
    Keywords: Isolated perfused rat kidney ; Micropuncture studies ; Cortisol reabsorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary It is still not clear whether a specific transport system for cortisol exists in the mammalian kidney. These experiments were carried out to analyze the cortisol reabsorption by the rat kidney using micropuncture techniques in situ as well as the isolated kidney preparation. During isolated kidney perfusion at a constant GFR of 1.01∓0.16 ml·g−1·min−1 35.3∓2.3% of the filtered cortisol was reabsorbed, when the load was varied by different cortisol concentrations in the perfusate. Variation of the GFR resulted in a fractional cortisol reabsorption of 42.7% at a tubular cortisol load of 20 ng·g−1·min−1 and of 25.3% at a load of 100 ng·g−1·min−1. Since in the isolated perfused rat kidney the fractional Na-reabsorption is dependent on the GFR, a linear correlation between fractional Na-reabsorption and fractional cortisol reabsorption could be shown. Similar results were obtained in the micropuncture studies. During microperfusion of proximal tubules 36∓4% of the intratubular cortisol were reabsorbed at a perfusion rate of 20 nl·min−1 (cortisol concentration of perfusate 39.5µg·1−1). Increase in perfusion rate to 40 nl·min−1 resulted in a decrease of fractional reabsorption to 18∓3%. Similar changes were obtained at a cortisol concentration of 375µg·1−1. Loop of Henle cortisol reabsorption showed a comparable dependency on flow rate, however, fractional cortisol reabsorption was significantly higher than in the proximal tubule. The total nephron including the collecting duct seems to be able to compensate for changes of cortisol reabsorption in the foregoing parts of the nephron. Neither in the isolated perfused kidney nor in the micropuncture studies a saturable transport maximum was obtained. Thus, the present results give no evidence for a specific transport system for cortisol in the rat kidney.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01851192
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  • 2
    Electronic Resource
    Electronic Resource
    Tubuloglomerular feedback control in kidneys of adrenalectomized rats (1980)
    Springer
    Pflügers Archiv 386 (1980), S. 11-19 
    Details
    ISSN: 1432-2013
    Keywords: Adrenalectomy ; Tubuloglomerular feedback ; Intratubular stop flow pressure ; Loop of Henle ; Diluting capacity ; Renal renin content ; Dexamethasone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The technique of orthograde tubular microperfusion has been used to test the functional integrity of tubuloglomerular feedback control in adrenalectomized rats. Kidneys of these animals display high renin contents, as well as an impairment of electrolyte transport in the loop of Henle, which was demonstrated by monitoring the electrical conductivity of fluid entering the distal tubule over a perfusion range of 10–50 nl/min. The calculated electrolyte concentration of the perfusion fluid leaving the loop of Henle was significantly higher in adrenalectomized rats than in controls. Intratubular stop flow pressure (SFP) during perfusion with a modified “endproximal” Ringer's solution was recorded continuously in early proximal segments at rates of 0–40 nl/min. Direct pressure transmission from perfused endproximal tubular segments to the pressure recording capillary was prevented by paraffin blockade of the intermediate proximal segment. An intact feedback response in each of the 32 tubules of the adrenalectomized rats studied was observed, which was reversible and could be demonstrated repetitively in individual tubules. Thus ΔSFP at 40 nl/min was −11.2±1.3 mm Hg in adx rats as compared to −8.1±1.3 in control rats. An increased freedback sensitivity was observed in dexamethasone treated adrenalectomized rats despite normal renal renin content. Here ΔSFP at 40 nl/min was −15±1.1. Thus, the feedback signal can be mediated in the apparent absence of adrenal steroid hormones and a high sensitivity of tubuloglomerular feedback control is not necessarily paralleled by high renin content of renal tissue.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00584181
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  • 3
    Electronic Resource
    Electronic Resource
    A new method for intratubular blockade in micropuncture experiments (1975)
    Springer
    Pflügers Archiv 354 (1975), S. 197-202 
    Details
    ISSN: 1432-2013
    Keywords: Micropuncture ; Intratubular Blockade ; Paraffin ; Petroleum Jelly
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Criteria for a reliable blockade of tubular flow are generally discussed and experimental evidence is presented that solid paraffin meets all the necessary criteria in rat kidney tubules when an immobile and tight sealing intratubular blockade is requested. A special microinjection apparatus for the application of paraffin is described. Furthermore, several alternative methods and materials have been tested and have been found to be inferior to solid paraffin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00579949
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  • 4
    Electronic Resource
    Electronic Resource
    Influence of aldosterone on epithelial leakiness of rat proximal tubules (1980)
    Springer
    Pflügers Archiv 385 (1980), S. 29-36 
    Details
    ISSN: 1432-2013
    Keywords: Adrenalectomy ; Proximal tubule ; Microconductivity probe ; Paracellular pathway ; Rat kidney
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Oil blocked superficial segments of late proximal tubules were perfused with salt free isosmolal mannitol solution. Time course of total net ion influx into the lumen after sudden stop of perfusion was monitored by continuous measurement of the conductivity of tubular fluid inside the lumen. Double barreled microelectrodes with high coupling resistance (R c=350–450 kOhm) were used as microconductivity probes. The observed time course was interpreted in terms of a two compartment system. Time constants for equilibration were 5.9±2.8 (SD) s in control rats, 14.4±8.0 s in adrenalectomized rats and 5.5±2.3 s in adrenalectomized rats substituted with 100 μg·kg−1 · d−1 aldosterone for 3 days. The observed effect of aldosterone on the equilibration time constant indicates that this hormone increases the leakiness of proximal tubular epithelium for passive ion influx into the lumen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00583912
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  • 5
    Electronic Resource
    Electronic Resource
    Electrical conductivity of tubular fluid of the rat nephron (1980)
    Springer
    Pflügers Archiv 383 (1980), S. 113-121 
    Details
    ISSN: 1432-2013
    Keywords: Conductivity measurements ; Diluting segment ; Furosemide ; Rat kidney ; Micropuncture experiments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Micropuncture experiments were performed to evaluate the electrolyte concentration of the tubular fluid (TF) in different segments of the rat nephron using the continuous, in situ measurement of electrical conductivity (ϰ) with a recently developed conductivity microprobe. In mid to late portions of proximal convoluted tubules (PCT) and in superficial distal tubules (DT) under free flow conditions the conductivities were 18.3±0.3 and 7.7±0.4 mS · cm−1 at 37°C, respectively. These values correspond to the conductivities of 137 and 58 mmol · l−1 sodium chloride solutions. The conductivity of the fluid in the inaccessible loop of Henle was examined by rapidly propelling its contents towards the conductivity pipette situated in the first accessible distal loop by a perfusion burst from the late proximal tubule. Thus, the free flow concentration profile existing along the ascending and descending limbs could be monitored with little distorsion. The transport functions of the different segments of Henle's loop, particularly of the diluting segment, were recorded using a “stop/pulse flow” method. Following blockade of a PCT the corresponding loop of Henle was perfused with a proximal equilibrium solution. Subsequently perfusion was interrupted for intervals of increasing duration to allow equilibration. The fluid collumn was then rapidly propelled into the distal tubule by suddenly re-establishing perfusion. Dilution of TF was found to proceed exponentially as a function of equilibration time. Minimal conductivity of TF in the thick ascending limb was reached after 25–30 s, the steady-state conductivity minimum being 3.9±0.24 mS · cm−1. This corresponds to the conductivity of a 27 mmol · l−1 NaCl solution. Addition of furosemide to the perfusion fluid (10−4 mol · l−1) resulted in a significant decrease of the dilution capacity, an effect which was enhanced by saline expansion of the animals. TF in contact with more proximal segments of Henle's loop i.e. the descending limb revealed a steady state conductivity of 17.7±0.3 mS · cm−1, which after correction for dilution in the ascending limb is equivalent to a 133 mmol · l−1 NaCl solution. The present technique provides a means to examine some of the transport properties of Henle's loop in vivo, particularly the dilution capacity of the ascending limb, which normally is not accessible to micropuncture.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00581871
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  • 6
    Electronic Resource
    Electronic Resource
    Tubuloglomerular feedback in rat kidneys of different renin contents (1975)
    Springer
    Pflügers Archiv 359 (1975), S. 33-56 
    Details
    ISSN: 1432-2013
    Keywords: Feedback-Control ; SN GFR ; Early proximal Flow Rate ; Stop Flow Pressure ; Flow Rate through Loop of Henle ; Kidney Renin Content ; Rat Kidney ; Micropuncture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Variations in flow rate through the loop of Henle in the range of 0–50 nl/min were induced using pressure controlled microperfusion. Simultaneously, with the aid of a second pressure-microperfusionsystem, the glomerular function of the same nephron was studied by continuous measurement of two parameters, early proximal flow rate (EPFR) and/or stop flow pressure (SFP). Elevation of loop perfusion above physiological values (40 nl/min) resulted in a drop of EPFR and SFP, whereas lowering perfusion rates had no effect. This feedback behaviour was studied in kidneys with different renin contents to test the role of the renin-angiotensin system in the mediation of the macula densa signal to the adjacent glomerular vessels. Renal renin content, measured after micropuncture experiments by incubation with substrate followed by radioimmunoassay of angiotensin I, was unaltered in control (Ia) and heminephrectomized rats (Ib), lowered in contralateral kidneys of 2 kidneys Goldblatt hypertensive rats (IIa), in DOCA- and salt-loaded rats (IIb), and in DOCA-, salt-loaded and heminephrectomized rats (IIc), and it was elevated in clipped kidneys of Goldblatt hypertension rats (IIIa). Micropuncture evaluation of the tubuloglomerular feedback behaviour in these experimental groups revealed the following results: 1. a feedback response under all conditions independent of the widely varying renin contents (1000-fold), 2. an asymmetrical behaviour of the feedback response in all kidneys as demonstrated by suppression of EPFR and SFP at elevated loop flow rates, but no change of these parameters when loop flow was interrupted, 3. compared to controls the decrease of each GFR parameter between 0 and 40 nl/min loop perfusion was lower in DOCA- and salt-loaded rats (IIb, IIc). Additional heminephrectomy (IIc) had no further influence on the reduced feedback response in DOCA- and salt-loaded rats, whereas this manoeuvre reduced the renal renin content drastically. A somewhat higher response than in controls was found in heminephrectomized rats (IIb) and in clipped kidneys of Goldblatt hypertensive rats (IIIa). These different magnitudes of feedback responses do not correlate with the renal renin content. It has been concluded, therefore, that renal renin activity is not the sole determinant of the effectiveness of the tubuloglomerular feedback response.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00581276
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  • 7
    Electronic Resource
    Electronic Resource
    Filtration in surface glomeruli as regulated by flow rate through the loop of henle (1974)
    Springer
    Pflügers Archiv 352 (1974), S. 315-337 
    Details
    ISSN: 1432-2013
    Keywords: SN GFR ; Feedback Control ; Flow Rate through Loop of Henle ; Proximal Free Flow- and Stop Flow Pressure ; Rat Kidney ; Micropuncture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A new pressure transducer microperfusion system has been used to measure quantitatively SN GFR, early proximal free flow pressure and stop flow pressure of varying flow rates through the loop of Henle in the range of 0 to 50 nl/min. Perfusing the loop with an isoosmolal artificial tubular fluid at physiological flow rates SN GFR was 19.9±1.1 and 27.7±1.0 nl/min in two different strains of antidiuretic rats. SN GFR increased when loop perfusion was interrupted. The question whether a feedback control mechanism of SN GFR is operative in the rat kidney was evaluated in further experiments in which early proximal tubular pressure was measured in functionally isolated proximal convolutions in vivo under conditions of constant flow as well as stopped flow. Experiments in which perfusion rate through the loop of Henle was varied demonstrated the existence of a feedback signal which originates downstream of the late proximal convolution and which affects filtration into individual early proximal segments. This feedback mechanism exhibited an asymmetrical behaviour: Elevation of loop perfusion above the control value resulted in an early proximal pressure drop, under simulated free flow conditions as well as under stop flow conditions. In contrast lowering of perfusion rate below the predetermined physiological value had no significant effect on early proximal pressures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00585685
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