Influence of various calcium intakes on calciuin-oxalate crystalluria in rats on sodium-oxalate diet

Forty adult male Wistar rats were placed in metabolic cageson a Ca-deficient diet (0.1%) for 7 days and then on a Ca-deficient,Na-oxalate (NaOx) enriched diet (20 mg/100 g) for another 14days. The animaLs were subdivided into three groups receivingthree different types of mineral water: group I (n=13), Badoit(Ca 222 mg/i); group II (n=14), Contrexéville (Ca 467mg/l);and group III (n=13), Evian (Ca 78 mg/l). Another series of25 rats (group I, n=9; group II, n=8; group III, n=8) underwentthe same study protocol, except that they received a normalCa diet (1%). On the low-Ca diet, urinary Ca-Ox monohydrate(COM) crystals were observed only under the Na-Ox diet, witha mean crystal number significantly greater in group III (16.7±4.5crystals/mm ) than in group I or II rats (2.5 ± 1.5 or4.1 ± 1.5 crystals/mm respectively). Urinary Ca concentrationsdecreased in all groups (/<0.001) under the Na-Ox diet, whileurinary oxalate concentrations increased in all groups (P<0.001).On the normal Ca diet, COM crystal excretion was observed onlywith the Na-Ox-enriched diet, but in this case feeding the Na-Oxdiet did not modify urinary oxalate excretion. Ca/Ox ratio wassignificantly lower under 0.1% Ca diet than under normal Cadiet, related with the type and the number of crystals observed,demonstrating that assessment of crystalluria can provide anindex of disease severity. Moreover, the hardness of the drinkingwater influ ences urinary COM crystal excretion only under alow-Ca, oxalate-rich diet, suggesting that the total calciumintake rather than the water calcium content is an importantfactor in the occurrence of Ca-Ox nephrolithiasis.