Bone resorption and Ca⁴⁵ turnover in growing rats

¹ Department of Biochemistry, College of Medicine, University of Illinois, Chicago, Illinois

A group of rats were maintained on a Ca⁴⁵ diet for 21 days, then sacrificed at varying time intervals after substituting a nonradioactive diet. The total calcium and calcium specific activity of several bones, blood and urine were determined. After correcting for the dilution of radioactivity due to an increase in total bone calcium, it was found that there was little, if any, loss of Ca⁴⁵ from rapidly growing bones. When the growth of the bone decreased, a small measurable loss was detected. It was assumed this slow loss of Ca⁴⁵ represented bone resorption. Values for the rate of bone resorption (replacement rates) are presented and their significance in the growth of the bone discussed.