The influence of dietary lipids on nephrolithiasis in rats

PURPOSE: The influence of dietary lipids on nephrolithogenesis is unclear. In the present study, I investigated the role of dietary lipids concerning both the etiology and the prevention of nephrolithiasis using 9-week-old male Wistar rats. METHODS: Study 1: The rats were divided into five groups and reared on standard, low protein, high protein and high cholesterol diets for 23 weeks. Study 2: The effects of cholesterol on nephrolithiasis was examined. The animals were given a 30 intraperitoneal injection of 2 ml of 8.5% calcium gluconate. Study 3: A nephrolithiasis model was prepared by intraperitoneal administration of 40 mg/kg of glyoxylic acid and 0.25 microgram of vitamin D3 daily for 2 weeks. The inhibitory effects of eicosapentaenoic acid (EPA) on nephrolithiasis were studied. RESULTS: Study 1: In the groups given the high protein and high cholesterol diets, an increase in renal osteopontin-mRNA, one of the major matrix ingredients of stones containing calcium, was observed. Study 2: Microlith was more frequently observed in the high cholesterol group than in the standard diet group. Study 3: In the EPA group, lithiasis was less extensively than in the groups administered distilled water or olive oil, and this was assumed to be caused by factors other than inorganic substances such as calcium and oxalic acid in the urine. When the renal tissue specimens in Studies 2 and 3 were examined, initial calcium deposition was found to start from the basement membrane of renal tubular cells and gradually spread throughout the cells. CONCLUSION: These results suggested that cholesterol is a risk factor in nephrolithiasis, and EPA is effective in its prevention. The elimination of hyperlipidemia should be included in dietary instructions for nephrolithiasis patients.