The influence of sex hormones on renal osteopontin expression and urinary constituents in experimental urolithiasis

Purpose: To our knowledge the influence of sex hormones on urinary stone fo rmation remains undetermined. We investigated the effect of castration on u rinary lithogenic factors and renal osteopontin expression in rats previous ly treated with ethylene glycol. Materials and Methods: Sprague-Dawley rats were divided normal males, castr ated males, males with 2 weeks of 0.75% ethylene glycol treatment, castrate d males with 2 weeks of 0.75% ethylene glycol treatment, normal females, ca strated females, females with 2 weeks of 0.75% ethylene glycol treatment an d castrated females with 2 weeks of 0.75% ethylene glycol treatment. We ana lyzed 24-hour urine samples for urinary constituents, such as calcium, oxal ate, citrate, uric acid, phosphate, magnesium, sodium, potassium and creati nine. The kidneys were examined for osteopontin expression by Northern blot analysis and for crystal deposition by histological examination. Results: In intact male rats calcium and citrate excretion decreased and ox alate excretion increased significantly after ethylene glycol treatment. Ca strated male rats with ethylene glycol had greater calcium and less oxalate excretion than male intact rats with ethylene glycol. In intact female rat s uric acid excretion decreased and only calcium excretion increased signif icantly after ethylene glycol treatment. Castrated female rats with ethylen e glycol excreted significantly more oxalate and less calcium than intact f emale rats with ethylene glycol. Renal osteopontin expression was the same in male intact and castrated rats, and in female intact and castrated rats. In males with ethylene glycol expression was stronger in castrated than in intact rats. In females with ethylene glycol expression was weaker in cast rated than in intact rats. No crystal deposits were found in the kidneys in any group. Conclusions: Testosterone appears to promote stone formation by suppressing osteopontin expression in the kidneys and increasing urinary oxalate excre tion. Estrogen appears to inhibit stone formation by increasing osteopontin expression in the kidneys and decreasing urinary oxalate excretion.