Low dose of human PTH(1-34) improved tibial subcortical bone mass without further cortical bone loss in adult intact beagles

Abstract

Cortical bone loss has not been observed in parathyroid hormone- (PTH-) treated rats, but clinical investigators suggest that it may augment cancellous bone mass at the expense of cortical bone in PTH-treated patients. In this study, the effects of PTH on cancellous and cortical bone mineral density of the tibia were studied in dogs with Haversian cortical bone remodeling by peripheral quantitative computed tomography (pQCT). Sixteen 19- to 20-month-old beagle dogs were randomized into four groups. In group 1, the vehicle control group, saline was injected daily throughout the experimental period. In group 2, the sequential group, 0.375 μg/kg of hPTH(1-34) was injected daily during the first 4 weeks, then stopped for 8 weeks, and this sequence was once repeated (on 4 weeks, off 8 weeks, and on 4 weeks, off 8 weeks). In group 3, the one-time group, the same dose of PTH was injected once per week for 24 weeks. In group 4, the three-time group, the same dose of PTH was given three times per week for 24 weeks. Peripheral QCT measurements were carried out 7 mm distal to the growth plate in the proximal metaphysis of the tibia. A voxel size of 0.295 mm and threshold for cortical and subcortical bone of 0.930 was chosen throughout the experiment. In adult beagles, group 4 had a significantly higher value in subcortical bone mineral density (SubCt.BMD) than control group (852 vs 771 mg/mm3; P < .05). Higher but non-significant increase occurred in the PTH-treated animals (groups 2, 3, 4) in the following parameters: total (Total.BMD), cancellous bone mineral density (Cn.BMD), cortical bone mineral density (Ct.BMD), and cortical thickness (Ct.Th). These findings show that a low dose of PTH improved subcortical bone mineral density without decreasing cortical bone mineral density during this dosage and period.