The effectiveness of intermittent rat parathyroid hormone (1-34) treatment on low bone mass due to oestrogen or androgen depletion in skeletally mature rats.

Rat parathyroid hormone (PTH) 1-34 (4 microg/kg/day) was applied for 2.5 months to 9 month-old rats immediately after ovariectomy or orchidectomy or to 15 month-old rats with low bone mass which had been castrated 6 months before in order to know the effects on serum biochemistry parameters, lumbar and femoral bone mineral density, histology, cancellous and cortical bone histomorphometry, mineralisation content profile in cortical bone by backscattered-electron microscopy, and femoral torsion biomechanical testing. In ovariectomised rats, preventive PTH treatment avoided cancellous bone loss in tibial metaphysis and partially in lumbar vertebra, while in cortical bone, PTH increased endosteal resorption and periosteal formation. In intervention study, PTH did not restore cancellous bone but a strong endosteal and periosteal new bone formation was detected. In orchidectomised rats, PTH, in preventive study, avoided cancellous bone loss in metaphysis and lumbar vertebra, and a mild new bone formation in cortical bone was found. In intervention study, PTH maintained baseline cancellous bone mass, but in cortical bone a strong endosteal and periosteal new bone formation was detected. The PTH-induced new bone formation was confirmed by histology and by mineral content profiles. After castration, biomechanical properties were affected in females but not in male rats and PTH reverted this effect.