Discrimination between Strontium and Calcium in Bone and the Transfer from Blood to Bone in the Rabbit

Abstract

Seven-month-old rabbits were injected intravenously with ⁹⁰Sr or ⁴⁵Ca and killed serially at time intervals from ten minutes to 460 days after injection. The uptake of both isotopes was about the same at ten minutes after injection. This uptake represented about one-third of the maximum uptake of ⁴⁵Ca, which was observed at one day and about half of the maximum uptake of ⁹⁰Sr which was observed at four hours. Although the maximum uptake of ⁴⁵Ca is greater than that of ⁹⁰Sr the rate of uptake and removal of ⁹⁰Sr was greater than that of ⁴⁵Ca. The turnover of both ⁹⁰Sr and ⁴⁵Ca was greater in the trabecular bone of the vertebrae and in the ends of the long bones than in the mid-cortex of the femur and tibia at short times after injection. Those portions of bone which showed the highest rates of turnover were found to be associated with relatively lower values for the stable strontium/calcium ratios. This suggested that the net effect of incorporation and release favoured the preferential retention of calcium at metabolically active sites. Measurements of stable strontium and calcium in the whole skeleton and in plasma showed an overall discrimination of about 1·6 in favour of calcium in the transfer from blood to bone.