Increased bone mineral density in aged rats with spontaneous mammary dysplasia.

Spontaneous mammary tumors were seen in seven of the 12 breeding female rats aged 2 years. All mammary tumors were diagnosed as mammary dysplasia (MD). Bone mineral contents (BMC) and bone mineral density (BMD) of their lumbar vertebrae and femur were determined using dual energy X-ray absorptiometry (DXA). In rats with MD, body weight (BW), BMD of the lumbar vertebrae and BMC of the femur were significantly higher than in the rats without MD. Although corpus luteum (CL) and follicles were seen in the ovaries of all animals, the number of CL in rats with MD was significantly lower than the rats without MD. It was suggested that high BMD, BW and decreased CL promoted mammary tumors.