INFLUENCE OF VARIOUS CALCIUM INTAKES ON CALCIUM-OXALATE CRYSTALLURIA IN RATS ON SODIUM OXALATE DIET

Forty adult male Wistar rats were placed in metabolic cages on a Ca-de ficient diet (0.1%) for 7 days and then on a Ca-deficient, Na-oxalate (NaOx) enriched diet (20 mg/100 g) for another 14 days. The animals we re subdivided into three groups receiving three different types of min eral water: group I (n = 13). Badoit (Ca 222 mg/l); group II (n = 14), Contrexeville (Ca 467 mg/l); and group III (n = 13), Evian (Ca 78 mg/ l). Another series of 25 rats (group I, n = 9; group II, n = 8; group III, n = 8) underwent the same study protocol, except that they receiv ed a normal Ca diet (1%). On the low-Ca diet, urinary Ca-Ox monohydrat e (COM) crystals were observed only under the Na-Ox diet, with a mean crystal number significantly greater in group III (16.7 +/- 4.5 crysta ls/mm3) than in group I or II rats (2.5 +/- 1.5 or 4.1 +/- 1.5 crystal s/mm3, respectively). Urinary Ca concentrations decreased in all group s (P<0.001) under the Na-Ox diet, while urinary oxalate concentrations increased in all groups (P<0.001). On the normal Ca diet, COM crystal excretion was observed only with the Na-Ox-enriched diet. but in this case feeding the Na-Ox diet did not modify urinary oxalate excretion. Ca/Ox ratio was significantly lower under 0.1% Ca diet than under nor mal Ca diet, related with the type and the number of crystals observed , demonstrating that assessment of crystalluria can provide an index o f disease severity. Moreover, the hardness of the drinking water influ ences urinary COM crystal excretion only under a low-Ca, oxalate-rich diet, suggesting that the total calcium intake rather than the water c alcium content is an important factor in the occurrence of Ca-Ox nephr olithiasis.