Bone metabolism and regulation of the blood calcium level in rats

Abstract

Combined kinetic (Ca45) and balance (Ca40) studies of young male Sprague-Dawley rats placed on three different levels of calcium intakes (0.05, 0.5, 1.0% Ca) showed that the blood plasma calcium level, as determined by atomic absorption spectrophotometry, remained constant and invariant over a range of absorption from 4.5 to 83.4 mg Ca/day and that the pool, i.e., all the exchangeable calcium in the body, did not increase with increased absorption. Hence no direct regulatory role can be attributed to the size of the pool. Measurement of the calcium deposition and resorption rates in bone showed that the former changed only little with increasing absorption, whereas the latter decreased nearly linearly under the same conditions. Calcium resorption from bone therefore appears to play the major role in regulating the blood calcium level.