In vivo bone mineral analysis throughout skeletal growth in rats: differences due to sex or vitamin D deficiency.

This study reports a new technique for the measurement of bone mineral content (BMC) in live rats. A single photon absorptiometric instrument has been adapted for rapid, reproducible measurement of BMC. Four bone sites were selected for use, based on ease of positioning and reproducibility of measurement; these were as follows: proximal femur, midfemur, proximal seventh caudal vertebra, and midseventh caudal vertebra. Significant increases were detected when BMC was measured at biweekly intervals from weaning to 18 weeks of age in normal male rats. Comparison of body growth and changes in BMC of male and female rats with age showed that body weight gain of female rats slowed earlier than that of male rats whereas BMC increased at similar rates in both sexes. Vitamin D deprivation from day 24 of life resulted in decreased BMC at all four measurement sites compared with such measurements in normal control rats. Differences were detectable after 8 weeks of age and occurred despite the maintenance of serum calcium levels within normal range and only slight reduction in body weights of vitamin D deprived rats. These studies demonstrate that single photon absorptiometry can be used to monitor changes in BMC in live rats on a routine basis without harm to the animals. Changes in BMC such as those due to growth or vitamin D deprivation can easily be quantitated using this technique.