Efficiency of 48h vs. 24h Injection of Parathyroid Hormone for Amelioration of Osteopenic Spine Properties in Male Rats

Daily application of parathyroid hormone (PTH 1-34) is used for treatment of osteoporosis. It was investigated whether orchiectomy-induced osteoporotic changes in spine can be ameliorated by every 48h administration of PTH in aged male rats. Eight-month-old male Sprague-Dawley rats were sham operated (n=24) or orchiectomized (Orx, n=36) and maintained untreated over 12 weeks. Thereafter, both tibia underwent transverse metaphyseal osteotomy (Komrakova et al. 2011, J Endocrinol; 209:9-19) and rats were divided into 5 groups treated s.c. as follows: 1) sham vehicle; 2) sham PTH every 24h (PTH/24h); 3) Orx vehicle; 4) Orx PTH/24h; 5) Orx PTH every 48h (PTH/48h). PTH dosage was 40 g/kg BW per injection. After 5 weeks, lumbar vertebral bodies were used in computed tomographical, biomechanical, histomorphological, ashing and gene expression analyses. Cortical and trabecular densities, biomechanical properties, serum osteocalcin level increased significantly after PTH treatments in all groups (yield load, sham: 232+17N, sham PTH/24h: 376+12N, Orx: 239+16N, Orx PTH/24h: 324+31N, Orx PTH/48h: 297+17N). Bone inorganic weight enhanced after daily PTH application in Orx rats. Bone gene expression did not differ (P>0.05) among the groups. Both PTH administration regimes (24h and 48h) improved impaired bone structure in osteopenic rats. Every 48h application was less effective, however, it improved bone properties to the level observed in healthy (sham) rats. Considering limitation of daily treatments known in humans, these results may be useful for further clinical studies.