Effects of Previous Calcium Intakes on Adaptation to Low and High Calcium Diets in Rats

Abstract

To study adaptation to low and high calcium diets, female weanling rats were fed for two periods in one of four ways: 1) a low calcium diet (0.2%) throughout both periods (LL); 2) a low calcium diet followed by a high calcium diet (0.9%) (LH); 3) a high calcium diet followed by a low calcium diet (HL); or 4) a high calcium diet throughout both periods (HH). Rats (LL and LH), accustomed to low intakes of calcium, retained a larger percentage of the dietary calcium than rats (HL and HH) accustomed to higher amounts of the element, regardless of whether the present calcium intake was low or high. Up to 133 days of age, the bones of the LL and LH groups contained less calcium and phosphorus per unit of bone weight than did the bones of the HL and HH groups. At 156 days of age (end of experiment), however, the bones of all groups contained equal concentrations of calcium and phosphorus. These data were interpreted to mean that body calcium stores control calcium retention. Parathyroid activity, as estimated by parathyroid gland weight and urinary phosphate values, was greater in the LL group than in the HL group. These data demonstrated that the adaptation to both high and low calcium diets was affected by previous dietary calcium levels and confirmed the idea that body stores of calcium control its retention.