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  • 1
    Electronic Resource
    Electronic Resource
    Nucleation and aggregation of calcium oxalate in whole urine; spectrophotometric sedimentation analysis: a new approach to study the aggregation of calcium oxalate dihydrate (2000)
    Springer
    Urological research 28 (2000), S. 147-154 
    Details
    ISSN: 1434-0879
    Keywords: Key words Urolithiasis ; Calcium oxalate ; Crystallization ; Aggregation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Spectrophotometric and scanning electron microscopic (SEM) studies of oxalate-induced crystallization have been performed in whole urine with and without continuous magnetic stirring and before and after millipore filtration of urine. With continuous stirring, preferential nucleation was observed and this followed second order kinetics. Important crystal aggregation only occurred after an oxalate load above 1 mmol/l and without stirring. Under these conditions and at an ionic calcium concentration of 2 mmol/l, single crystals and aggregates of calcium oxalate dihydrate and monohydrate of well defined sizes were produced. Single dihydrates, their aggregates and the other particles could be distinguished by their significantly different sedimentation rates. From sedimentation curves an aggregation ratio for calcium oxalate dihydrate (aggregated/total dihydrate particles) was extrapolated. Millipore filtration removing important urinary macromolecules increased this aggregation ratio as well as the size of the aggregates on SEM pictures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002400000108
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Automated and computer-controlled method for the measurement of the crystallization of calcium oxalate monohydrate in urine (1995)
    Springer
    Urological research 23 (1995), S. 407-411 
    Details
    ISSN: 1434-0879
    Keywords: Urolithiasis ; calcium oxalate ; Crystal growth ; Ion-selective electrode ; Automated kinetic measurement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Monitoring of crystallization of calcium salts with ion-selective electrodes has turned out to be a very sensitive method. The difficulties of handling these electrodes in native whole urine and other biological fluids have been eliminated by new calcium analyzers, which clean and calibrate the electrodes after each measurement. To study crystallization kinetics, repeated calcium ion measurements have to be performed at regular intervals. For this purpose we have developed a special sampler and software. The sampler brings a thermostat-controlled crystallization chamber to the analyzer at preselected intervals. The computer directs and coordinates the sampler and the analyzer, stores the received results and prints out growth curves. Furthermore it calculates the half-time (h) and the maximum decrease of ionic calcium at infinite incubation time (ΔCa ∞ 2+ ). Both values are shown to characterize the growth of calcium oxalate monohydrate in urine. Results are obtained within 40 min.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00698744
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    The influence of hydroxyapatite and pyrophosphate on the formation product of calcium oxalate at different pHs (1989)
    Springer
    Urological research 17 (1989), S. 153-155 
    Details
    ISSN: 1434-0879
    Keywords: Calcium oxalate ; Heterogeneous nucleation and growth ; Inhibitors ; Pyrophosphate ; Hydroxyapatite
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The nucleating effect of hydroxyapatite (HAP) and the inhibitory effect of pyrophosphate (PPi) on calcium oxalate crystallization have been studied at different pH's in solution metastabely supersaturated with respect to calcium oxalate but saturated with respect to HAP. Crystallization was monitored by a decrease of calcium in the supernatant and formation products were calculated. At a pH above 6.0 already minimal HAP concentrations proved to be a suitable substrate for heterogeneous nucleation and growth of calcium oxalate. PPi showed a pronounced inhibitory effect on spontaneous as well as on HAP induced crystallization of calcium oxalate, this effect being highly pH dependent. HAP was found to neutralize the inhibitory effect of PPi in a molar ratio of 10:1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00256242
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Rapid method of measuring the inhibition of calcium-oxalate monohydrate growth in urine (1990)
    Springer
    Urological research 18 (1990), S. 219-222 
    Details
    ISSN: 1434-0879
    Keywords: Inhibitors ; Calcium-oxalate monohydrate growth ; Pyrophosphate ; Citrate ; Urine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In order to have a rapid method of measuring the inhibition of calcium-oxalate monohydrate growth in freshly voided whole urine, a test system by Meyer and Smith that has originally been developed for diluted urine was modified. The crystallization processes were monitored by an ion-selective calcium electrode, which allowed determination of the half-life value of the decrease in calcium within 25 min. Even given the high inhibitory activity of whole urine, the test gave reliable results when a high seed concentration was used. Inhibition was expressed as the ratio between the half-lives of the calcium decrease obtained in the presence and in the absence of inhibitors. This approach allowed kinetic studies of individual inhibitors in model solutions. Furthermore, the measurements of inhibitors in urine could be, performed before the chemical composition was determined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00295851
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    Paper (German National Licenses)
    Fulltext
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