The effect of ovariectomy on periosteal bone formation and bone resorption in adult rats.

In order to quantify the rate of bone metabolism after ovariectomy, tetracycline was injected intraperitoneally into 3-month-old female Wistar rats to label the mineralizing front and ovariectomy was performed. The rats were sacrificed 91 days later, whereupon serum calcium and phosphorus were determined. The femurs were sectioned in the upper part, photographed and the area between the tetracycline line and the outer perimeter of the bone was planimetered at a reference point. The area of periosteal bone formed was noted to be 28.3% greater than in control rats (P = 0.0002) and the area of the medullary cavity 18.8% larger (P = 0.033), indicating enhanced osteoblast and osteoclast function. The serum calcium concentration was unchanged, but a significant reduction in phosphorus was seen in the ovariectomized rats (P < 0.0001). The data suggest that the stimulated bone formation is a representative phenomenon in ovariectomized rats at least for 100 days and bone resorption remains elevated in the course of processes possibly leading to osteoporosis.