PARATHYROID-HORMONE-(1-34) INCREASED TOTAL-BODY BONE MASS IN AGED FEMALE RATS

Daily subcutaneous administration of bovine parathyroid hormone (PTH)( 1-34) stimulates bone formation and increases bone mass in rat tibiae, femora and lumbar spine. However, the effects of PTH on the whole bod y bone mineral content and density determined by dual energy x-ray abs ortiometry (DEXA) have not been previously reported in rats. Eighteen- month-old intact female rats were subcutaneously injected daily with 0 , 40, 80 or 160 mu g/kg/day of bovine PTH (1-34) for either 15 or 60 d ays. Whole body DEXA was performed at 1 day before autopsy, and bone a rea, bone mineral content (BMC) and bone mineral density (BMD) of the total body were determined. Total femoral, tibial and lumbar spine BMD was also determined ex vivo. Cancellous bone histomorphometry was per formed on sections of double-labeled proximal tibial metaphyses. Whole body bone mineral content and density were significantly increased by 60 days, but not by 15 days, of PTH treatment at all dose groups comp ared with vehicle controls. Lumbar vertebral and total femoral BMD was significantly increased at all doses of PTH by 15 days of administrat ion and further increased by 60 days. All doses of PTH increased trabe cular bone area in proximal tibial metaphyses by 15 days and further i ncreased by 60 days. In proximal tibial cancellous bone, dose-dependen t increases in percent labeled perimeter, mineral apposition rate and bone formation rate-bone volume referent were found between 40 and 160 mu g/kg of PTH treatment by 15 days, and no further increases were fo und by 60 days. Our results showed that in aged female rats, bovine PT H(1-34) increased bone formation and total body bone mass.