No abstract

Various methods and techniques are aimed at modelling crystallisation processes of urinary stone formation in vitro. There are considerable differences between them in technical and physico-chemical principles, quantification of crystal nucleation, growth and agglomeration and the parameters measured. In this paper, some important in vitro systems are described as examples. They are compared with regard to some of their features and capabilities. Emphasis has been placed on evaluation of the physiological relevance of the methods. For that reason, the different in vitro models have been related to current views on intrarenal in vivo, mechanisms underlying stone formation and other independent experimental results. Crystallisation procedures carried out in aqueous solutions are likely to mimic crystalluria, corresponding to a free-particle mechanism. However, a specifically tailored flow technique of crystallisation in gels seems to be a reasonable model of stone formation, in accordance with the generally accepted fixed-particle theory.

In this study, an efficient microtechnique (gel crystallization method) was used to investigate the in-vivo effect of sodium-potassium citrate on the crystal growth rate of calcium oxalate (Vcr) in human urine samples of 6 healthy volunteers. With a daily dose of 3 X 11 mmol of alkali citrate, Vcr decreased by 70%. This could have been due to the decrease of calcium excretion, which caused 50-60% of the total change, and to the increase of citrate and pH, each contributing about 20-25% to the decline of Vcr. The findings explain the clinical advantages of alkali citrates in the prevention of recurrent calcium oxalate stone formation.

We developed an eleetronic control unit for the determination of oxalate in urine by isotachophoresis with the LKB 2127 Tachophor. It permits a considerable reduction of the time required for analysis. Measurements were carried out in samples of untreated urine using different leading electrolytes and standardization procedures. Determination of oxalate can be thus achieved within 25 min, whereof the manpower expenditure is about 5 min. In the ränge of 1.0-0.1 mmol/1 urinary oxalate can be determined with a coefficient of Variation of 4-6%. The detection limit of the method is about 0.04 mmol/1. * Bestimmung von Urinoxalat durch Isotachophorese -Praktische Verbesserungen und kritische BewertungZusammenfassung: Es wird ein Zusatzgerät zur Isotachophorese-Apparatur LKB 2127 Tachophor beschrieben, das eine Verkürzung der Analysenzeit zur Bestimmung von Oxalat im Harn ermöglicht. Oxalatbestimmungen wurden im nichtvorbehandelten Urin mit verschiedenen Leitelektrolyten durchgeführt und unterschiedlich ausgewertet. Der Messung bei pH 2.3 (Leitelektrolyt enthält HC1 und NaCl) ist wegen der größeren Effektivität und Richtigkeit der Vorrang zu geben. Eine Bestimmung erfordert 25 min bei einem tatsächlichen Arbeitszeitaufwand von etwa 5 min. Im Bereich l ,0-0,1 mmol/1 Oxalat liegt der Variationskoeffizient zwischen 4 und 6%. Die Nachweisgrenze ist etwa 0,04 mmol/1. Introducrion

Drinking therapy and lowering of urinary oxalate excretion can be concluded to be the most promising means of preventing CaOx urolithiasis. The new crystallization model demonstrated here should be suitable to new applications in the investigation of urinary stone formation.