Effect of intermittent administration of hPTH(1-34) on cortical bone geometry in rats treated with high-dose glucocorticoids.

High-dose glucocorticoids reduce cortical bone gain in rats. The aim of the present study was to examine the effect of the intermittent administration of human parathyroid hormone (1-34) (hPTH[1-34]) on cortical bone in rats treated with high-dose prednisolone (PSL). Twenty-five female Sprague-Dawley rats (6 weeks old) were randomized into the following three groups: a vehicle administration (control) group, a PSL (10 mg/kg s.c., 5 times a week) administration group, and a PSL + hPTH(1-34) (30 μg/kg s.c., 3 times a week) administration group. After 8 weeks of treatment, the bone mineral density (BMD) of the femoral diaphysis was determined using peripheral quantitative computed tomography, and a static bone histomorphometric analysis was performed on the tibial diaphysis. PSL administration induced a decrease in the BMD of the femoral diaphysis, compared with the control group, as well as decreases in the total tissue area, cortical area, percent cortical area, and periosteal perimeter and increases in the marrow area, percent marrow area, and endocortical perimeter of the tibial diaphysis, compared with the control group. The intermittent administration of hPTH(1-34) to PSL-treated rats attenuated PSL-related changes in the BMD of the femoral diaphysis and the percent cortical area, marrow area, percent marrow area, and endocortical perimeter of the tibial diaphysis. The findings of the present study suggest that the intermittent administration of hPTH(1-34) improves cortical BMD, acts on the endocortical bone surface, and improves cortical bone geometry, in rats treated with highdose PSL.