[*calcium-oxalate lithogenesis: crystallization in the presence of urine from healthy subjects].
In the present study we aim at describing the influence of urine of non-lithiasic subjects on the different crystallization stages of calcium oxalates. The experimental method consists in comparing the turbidimetric curves obtained by crystallization in pure synthetic urine to the curves obtained after addition of natural urine to the solution. Natural urine plays an important role on nucleation, crystal growth and agglomeration even if only small amounts (4% v/v) are added to the mother solution. Nucleation is favoured (decrease of the induction period and increase of the crystal number) by the presence of solid particles, such as cellular fragments, which play the role of substrates for heterogeneous nucleation. On the other hand, both the growth rate of the crystals and their degree of agglomeration are reduced. Moreover, the physical nature of the crystals which precipitate is different from that of the crystals which nucleate in synthetic urine. Under our conditions of high super-saturation, natural urine favours the nucleation of calcium oxalate dihydrate at the expenses of calcium oxalate trihydrate which forms in pure synthetic urine. A hypothesis on the origin of the lithogenesis process is made and a correlation between the localization of the calcium oxalate stones in the urinary tracts and their main constituents is proposed.