Crystallization in the nephron.
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Animals↗
Biomedical subjects
I Højgaard
Publications and source records attributed to I Højgaard.
The effect of pH changes on the crystallization of calcium salts in solutions with an ion composition corresponding to that in the distal tubule.
The effect of pH changes on the crystallization in solutions with an ion composition assumed to correspond to that of urine in the distal part of the distal tubule was examined by recording the number and volume of crystals with a Coulter Multisizer and by studying the crystal morphology with scanning electron microscopy at different degrees of volume reduction. The experiments were carried out with 100 ml samples at different starting pH values without and with 20% of dialysed urine (dU). The number of crystals increased in response to the volume reduction. In solutions without dU, 100 or more crystals with a diameter in the range 2.4-45 microm were observed already at a volume reduction of 40% when the initial pH was 7.28. For solutions with a pH of 5.80 and 6.45 the corresponding values were 60% and 80%, respectively. In the presence of dU, an appearance of crystals was recorded at volume reductions of less than 20%. In solutions with an initial pH of 5.80 and 6.45, the crystal number was greater with dU than without; such a difference was not recorded at pH 7.28. In samples containing dU, the mean crystal volume (MCV) varied very little when the sample volume was reduced. The same was found in solutions without dU when the initial pH was 5.80 and 7.28, whereas the MCV was greater in the samples with pH 6.45. Scanning electron microscopy of solutions reduced to 30-40% of the original volume showed that calcium phosphate had formed in solutions with a starting pH of 7.28 and 6.45. In solutions with pH 5.80 calcium oxalate crystals were observed with calcium phosphate.
Calcium Oxalate↗
Crystallization during volume reduction of solutions with a composition corresponding to that in the collecting duct: the influence of hydroxyapatite seed crystals and urinary macromolecules.
To examine the effect of hydroxyapatite (HAP) seed crystals and urinary macromolecules on the crystallization under conditions similar to those in the collecting duct, we evaporated 100 ml samples of salt solutions with an ion composition assumed to correspond to that in the collecting duct without and with HAP seed crystals. The crystallization in seeded solutions was assessed both with and without dialysed urine (dU). After evaporation the number and volume of crystals were recorded in a Coulter Multisizer and the crystal morphology examined with scanning electron microscopy (SEM) and X-ray crystallography. Addition of HAP crystals was apparently followed by an approximately 15-20% increase in heterogeneous nucleation of calcium oxalate (CaOx). In these experiments SEM and X-ray crystallography showed a high percentage of CaOx in the precipitate. In samples reduced to 40-69 ml, addition of dU to the collecting duct solution containing HAP seed resulted in a greater mean (SD) number of crystals; 3895 (1841) in samples with dU and 1785 (583) in samples without. This was mainly explained by an increased mean (SD) number of small crystals. The mean crystal volume was 17.8 (1.1) and 34.3 (9.1) in samples reduced to 40 69 ml with and without dU, respectively. This might reflect the inhibitory effect of dU on the growth and/or aggregation of the CaOx-CaP precipitate or a promoted nucleation resulting in a large number of small crystals. It is concluded that calcium phosphate formed above the collecting duct might induce heterogeneous nucleation of CaOx at lower levels of the renal collecting system, and that urinary macromolecules are powerful modifiers of these processes.
Calcium Oxalate↗
Some aspects of the intratubular precipitation of calcium salts.
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Calcium Oxalate↗
The effects of citrate and urinary macromolecules on the aggregation of hydroxyapatite crystals in solutions with a composition similar to that in the distal tubule.
The effects of citrate and dialysed urine (dU) on the aggregation of hydroxyapatite (HAP) crystals in solutions with different pH and otherwise with an ion composition assumed to correspond to that in the distal part of the distal tubule were studied by spectrophotometric assessment of the rate of crystal sedimentation. When the concentration of dU was increased from 1% to 20% we recorded an increased inhibition of HAP crystal aggregation at pH 6.5. There were no differences in the inhibition accomplished by 10% dU when the pH was varied between 5.5 and 7.0, but a lower inhibition was recorded at pH 7.5. Citrate in the range 0.05-4 mmol/l had a concentration-dependent inhibitory effect on HAP crystal aggregation. In the presence of 10% dU the net inhibitory effect of citrate was reduced at all pH levels. In the pH interval 5.5-7.0 a higher inhibition was recorded with 0.5 mmol/l citrate than with 10% dU, but in the presence of dU there was only a minor additional effect of citrate at concentrations below 0.5 mmol/l. These findings indicate that urinary macromolecules present in dU strongly inhibit HAP crystal aggregation under solution conditions corresponding to those in distal tubular urine. At the same nephron level citrate might have a direct inhibitory influence on the aggregation of HAP crystals, but in the presence of normal urinary macromolecules the additive inhibitory effect of citrate is probably only marginal.
Citric Acid↗
The influence of hydroxyapatite seed on the crystallization induced by volume reduction of solutions with an ion composition corresponding to that in the distal tubule at different pH levels.
OBJECTIVE: To simulate the crystallization process that might occur in the nephron segment from the distal part of the distal tubule (DTd) to the end of the collecting duct (CD), we evaporated salt solutions with an ion composition assumed to correspond to that in the DTd. MATERIAL AND METHODS: 100-mL samples of DTd solutions with and without dialysed urine (dU) and with hydroxyapatite (HAP) seed crystals were evaporated to a final volume of 10-20 mL at different starting pH levels. After evaporation, the number and volume of crystals were recorded in a Coulter Multisizer and the crystal morphology examined by scanning electron microscopy and x-ray crystallography. RESULTS AND CONCLUSIONS: Volume reduction of solutions with a pH of 6.5 resulted in a crystallization of calcium phosphate (CaP) and calcium oxalate (CaOx). An increased fraction of CaOx in the precipitate was observed when the pH was decreased. In solutions with an initial pH of 5.5, 6.0 and 6.5, the number and volume of crystals were smaller in samples analysed after 60 min than in those analysed immediately after the evaporation. This might reflect dissolution of crystals, as expected, most pronounced in the most acid solutions, but apparently counteracted by dU. The results obtained in these experiments suggest that CaP formed high in the nephron might induce heterogeneous nucleation of CaOx when subjected to the lower pH levels and increased supersaturation with CaOx encountered in the CD. With an alkaline pH in the CD, a pronounced crystallization of CaP can be anticipated.
Calcium Oxalate↗
Crystallization during volume reduction of solutions with an ion-composition corresponding to that in the distal tubuli.
The effect of macromolecules on the crystallization in solutions with an ion-composition and a pH corresponding to that of urine in the distal part of the distal tubuli was examined by recording the number and volume of crystals in a Coulter Multisizer and by studying the crystal morphology with scanning electron microscopy at different degrees of evaporation. The experiments were carried out with 100 ml samples of salt solutions with and without different concentrations of dialysed urine (dU) from normal subjects. Addition of dU resulted in a greater number of crystals and a reduction in the mean crystal volume (MCV). Under the experimental conditions, the maximal effect of the macromolecules appeared to be accomplished in solutions with an initial dU concentration of 10%. The precipitate was strongly suggestive of calcium phosphate (CaP) as shown by scanning electron microscopy and Raman spectroscopy. This conclusion was further supported by the ion-activity products of calcium oxalate (CaOx) and different CaP salts in those samples in which crystal formation was recorded. The obtained results give support to the view that macromolecules might exert a promotive effect on the nucleation of CaP. The macromolecules also appear to counteract the development of large CaP crystals, but whether this is due to an inhibition of crystal growth, an inhibition of crystal aggregation or both could not be concluded from these experiments. The way in which CaP crystals initially form in the nephron might be of importance for the subsequent crystallization of CaOx and the formation of CaOx containing stones.
Calcium Oxalate↗