The Concentrations and Ratio of Dietary Calcium and Phosphorus Influence Development of Nephrocalcinosis in Female Rats

Nephrocalcinosis (NC) in female rats can complicate the interpretation of nutritional or toxicological studies involving the kidney. Recent reformulations of standardized rodent diets such as AIN-93G and NTP-2000 sought to optimize the dietary Ca:P ratio, an important etiologic factor in NC. The effect of increasing intakes of Ca and P together at their optimal molar ratio has not been systematically studied. Weanling female and male Sprague-Dawley rats were fed modified AIN-93G diets containing Ca and P at AlN-93G diet concentrations (5 g Ca + 3 g P/kg diet), with multiples of Ca and P at the same ratio (1.5x = 7.5 g Ca + 4.5 g P, 2.5x = 12.5 g Ca + 7.5 g P, 4.0x = 20.0 g Ca + 12.0 g P/kg diet), or Ca and P at concentrations found in the AIN-76A diet (5 g Ca + 5 g P/kg diet), for 16 wk. Incidence and severity of NC and kidney Ca concentration in female rats increased with dietary Ca and P, although not to levels in female rats fed at the AIN-76A Ca:P ratio. Male rats showed limited evidence of kidney Ca accumulation or NC. The concentrations of dietary Ca and P, as well as the ratio of these two elements, affected development of NC in female rats.