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  • 1
    Electronic Resource
    Electronic Resource
    Handling of uric acid by the rat kidney (1972)
    Springer
    Pflügers Archiv 335 (1972), S. 257-265 
    Details
    ISSN: 1432-2013
    Keywords: Uric Acid Reabsorption ; Uric Acid Secretion ; Microperfusion ; Proximal Tubule of the Rat Kidney
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Under free flow conditions there is a net transport of uric acid in the rat proximal tubule. This net transport is the result of two unidirectional fluxes which in the range of normal plasma concentrations of uric acid follow a first order kinetic, i.e. the unidirectional fluxes are in linear proportion to uric acid concentration in tubular fluid or in plasma, respectively. The transport coefficient of the influx (in secretion direction) exceeds that of the outflux (in reabsorption direction) by a factor of 2.5.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00586216
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  • 2
    Electronic Resource
    Electronic Resource
    In vivo studies on uricase activity in the rat (1974)
    Springer
    Pflügers Archiv 351 (1974), S. 323-330 
    Details
    ISSN: 1432-2013
    Keywords: Uricase ; Urate ; Allantoin ; Liver ; Kidney ; Microperfusion ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 1. In vivo uricase activity was tested in rats by injection of 2-C14 urate and measurement of the total C14 activity and the fractional activities of allantoin, allantoic acid and urea in samples of blood and urine. In control animals, 5 min after the injection, 70% of the plasma tracer was already present in the form of allantoin. No allantoic acid and urea were produced. Intestinectomy had no measurable influence on uricase activity. On the other hand, hepatectomy or ligation of the hepatic artery combined with subtotal viscerectomy did abolish uricase activity almost completely. 2. Following microinjections into proximal tubules of Ringer solution containing 2-C14 urate, urine samples during early recovery mainly contained labelled urate, whereas in later samples the fraction of labelled allantoin increased. About 12 min after the microinjection the urine of both kidneys contained equal amounts of tracer mainly in the form of allantoin. 3. When segments of proximal tubules were perfused with an equilibrium solution containing tracer amounts of C 14 urate, no urate was metabolized during its passage through the proximal tubule. 4. C 14 urate was offered from the peritubular capillaries and samples of tubular fluid were analyzed, Again, all the tracer in the tubular fluid was in the form of urate, indicating that urate is not oxidized when it is transported across the tubular cell. It is concluded from these results that: 1. The rat kidney has no significant uricase activity. 2. Urate transport in the kidney is not influenced by this enzyme. 3. The degradation of urate to allantoin takes place at extrarenal sites, mainly in the liver.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00593318
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  • 3
    Electronic Resource
    Electronic Resource
    Micropuncture evaluation of the importance of perivascular pH for the arteriolar diameter on the brain surface (1970)
    Springer
    Pflügers Archiv 316 (1970), S. 152-163 
    Details
    ISSN: 1432-2013
    Keywords: Cerebral Circulation ; Cerebral Arteriolar Resistance ; Local Arteriolar Reactions ; Smooth Muscles ; Hydrogen Ions ; Gehirndurchblutung ; Widerstand der Gehirnateriolen ; Lokale arterioläre Gefäßreaktion ; Glatte Muskelzelle ; Wasserstoffionen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A micropipette technique was used to induce local changes of the bicarbonate concentration of the cerebro-spinal fluid surrounding arterioles on the exposed cerebral cortex of anaesthetized rats and cats. Injection volumes of a few nanoliters caused circumscribed and pronounced changes of the diameter of the arterioles under study: mock spinal fluid without bicarbonate dilated, while a solution containing 25 meq/l of bicarbonate constricted the vessels. In such experiments the localpCO2 of the arteriolar wall remains practically constant, since it is set by thepCO2 of the arterial blood and of the cerebral tissue. Hence the microinjections essentially consisted in a local change of the pH of the fluid surrounding a small segment of a cerebral arteriole. Since metabolic changes of the nervous tissue changes the periarteriolar pH, it is probable that local pH induced vasomotor changes of the type reported here participate in the so called metabolic regulation of the cerebral blood flow which underlies the local adaptation of the cerebral blood flow to changing functional demands.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00586483
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  • 4
    Electronic Resource
    Electronic Resource
    Handling of uric acid by the rat kidney (1971)
    Springer
    Pflügers Archiv 324 (1971), S. 279-287 
    Details
    ISSN: 1432-2013
    Keywords: Uric Acid Secretion ; Micropuncture ; Renal Tubule ; Ultramicro Analysis ; Harnsäuresekretion ; Mikropunktion ; Nierentubulus ; Ultramikroanalyse
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Mit Hilfe der Mikropunktionstechnik und einer neu entwickelten Methode der Ultramikroanalyse wurde der Harnsäuretransport am proximalen Tubulus der Rattenniere untersucht. Unter normalen Bedingungen ohne Harnsäureinfusion und ohne osmotische Diurese konnte eine Harnsäure-Netto-Sekretion im proximalen Tubulus nachgewiesen werden. Dabei war in diesen Experimenten die Inulinclearance etwa doppelt so groß wie die Harnsäureclearance. In der Bilanz wurde also mehr Harnsäure resorbiert als sezerniert, aber nicht, wie früher angenommen, im proximalen Tubulus.
    Notes: Summary Uric acid transport in the rat proximal tubule was studied by micropuncture and a new method of chemical ultramicro analysis. Under normal free-flow conditions at physiological levels of uric acid plasma concentrations a net secretion of uric acid in the proximal tubule was demonstrated. In these experiments the clearance ratio of uric acid to inulin was in the range of 0.4 which is normal in antidiuretic rats. Net reabsorption of uric acid, therefore, took place in the kidney, but certainly not in the proximal tubule as previously suggested.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00592456
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  • 5
    Electronic Resource
    Electronic Resource
    Buchbesprechungen (1971)
    Springer
    Journal of molecular medicine 49 (1971), S. 170-176 
    Details
    ISSN: 1432-1440
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01496816
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  • 6
    Electronic Resource
    Electronic Resource
    Handling of uric acid by the rat kidney (1973)
    Springer
    Pflügers Archiv 338 (1973), S. 295-302 
    Details
    ISSN: 1432-2013
    Keywords: Uric Acid Reabsorption ; Uric Acid Secretion ; Microperfusion ; Proximal Tubule of the Rat Kidney
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In volume constant microperfusion experiments a steady state ratio of uric acid concentration in tubular fluid and plasma of aproximately 2.5 is found. An extrapolation to free flow conditions shows agreement with previous micropuncture results. This finding supports the view that uric acid undergoes net secretion in the proximal tubule of the rat kidney. It is discussed that the low uric acid clearance of the intact kidney is mainly caused by uric acid reabsorption in the loop of Henle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00586071
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  • 7
    Electronic Resource
    Electronic Resource
    Urate handling by the rat kidney (1974)
    Springer
    Pflügers Archiv 352 (1974), S. 115-120 
    Details
    ISSN: 1432-2013
    Keywords: Urate ; Reabsorption ; Loop of Henle ; Micropuncture ; Microperfusion ; Microinjection ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Reabsorption rates for urate in the loops of Henle were measured in superficial nephrons in the rat 1. under conditions of free flow, 2. using microperfusion and 3. by a microinjection technique. 1. Under conditions of free flow distally measured TF/PUA/TF/PIn-values varied between 0.51 and 0.38 in antidiuretic rats, depending on TF/PIn (UA = both uric acid and urate, In = inulin, TF/P = concentration in tubular fluid to plasma concentration). The corresponding values in samples from end-proximal tubules were 1.06 and in urine 0.19 (U/PUA/U/PIn). 2. In microperfusion experiments of Henle loops early distal recoveries of 2-C14 urate varied between 57 and 86%, depending on the flow rates (10–40 nl/min). 3. In microinjection experiments C14 recovery in urine was about 85% when tracer solution was microinjected into endproximal tubules. From these results we conclude: 1. The main site of urate reabsorption is located in the loops of Henle. 2. This reabsorption is highly dependent on flow rates. Increase of flow rate through Henle's loop decreases urate reabsorption.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00587510
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  • 8
    Electronic Resource
    Electronic Resource
    Urate interaction with plasma proteins and erythrocytes (1974)
    Springer
    Pflügers Archiv 352 (1974), S. 121-133 
    Details
    ISSN: 1432-2013
    Keywords: Urate ; Protein Interaction ; Uptake by Erythrocytes ; Renal Reabsorption ; Man ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Interaction of urate with human and rat plasma was studied by a dialysis technique at different temperatures. At 4° C a certain fraction of urate is bound to proteins. However, this fraction diminishes with increasing temperature and at 37° C only some 7–8% (in man) and 2% (in rat) interact with proteins. The finding that urate is almost completely filtered in the glomerulus is discussed. In body areas exposed to low temperatures protein binding of urate may be of importance. Urate uptake by erythrocytes is characterized by two components: a fast component equilibrating almost immediately at about 7% in man and 17% in rat and a slow component reaching equilibrium after 60 min, at 28% and 36%, respectively. The process is described by a mathematical formula. Lowering of the temperature mainly diminishes uptake by the slow component withQ 10-values ranging between 1.5 and 4.0. In the observed range of concentrations the uptake process does not saturate. The results at lower pH-values suggest that it is unionized uric acid which is transported by the slow component. Application of the data to kidney medulla supports the hypothesis that erythrocytes and, probably, to a lesser extent plasma proteins serve as vehicles for urate reabsorption in the countercurrent system. Such a temporary interaction enables uric acid to escape recirculation and to leave the kidney medulla.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00587511
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