Increased intracortical bone remodeling during lactation in beagle dogs

There are substantial changes in skeletal and mineral metabolism during pre gnancy and lactation. The purpose of this study was to determine the change s in intracortical bone remodeling and turnover during lactation in beagle dogs. A femur and rib were obtained from dogs near the end of lactation or soon after weaning and compared with nonlactating controls. Rib cortical bo ne had much higher bone turnover rates than did femoral diaphyseal cortical bone. The number of single-labeled osteons and the number of resorption sp aces were significantly greater during lactation in both the rib and the fe mur. Additionally, the mineral apposition rate, basic multicellular unit ac tivation frequency, and bone turnover rates were greater in the femoral cor tical bone from the lactating dogs than from the controls. These data demon strate that during lactation, intracortical bone remodeling increases, and this may provide a mechanism for the skeleton to be responsive to the calci um requirements of the mother. In addition, these data may help explain the transient decreases in cortical bone mineral density that are reported to occur during human lactation.