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Programmed administration of parathyroid hormone increases bone formation and reduces bone loss in hindlimb-unloaded ovariectomized ratsGonadal insufficiency and reduced mechanical usage are two important risk factors for osteoporosis. The beneficial effects of PTH therapy to reverse the estrogen deficiency-induced bone loss in the laboratory rat are well known, but the influence of mechanical usage in this response has not been established. In this study, the effects of programed administration of PTH on cancellous bone volume and turnover at the proximal tibial metaphysis were determined in hindlimb-unloaded, ovariectomized (OVX), 3-month-old Sprague-Dawley rats. PTH was administered to weight-bearing and hindlimb-unloaded OVX rats with osmotic pumps programed to deliver 20 microg human PTH (approximately 80 microg/kg x day) during a daily 1-h infusion for 7 days. Compared with sham-operated rats, OVX increased longitudinal and radial bone growth, increased indexes of cancellous bone turnover, and resulted in net resorption of cancellous bone. Hindlimb unloading of OVX rats decreased longitudinal and radial bone growth, decreased osteoblast number, increased osteoclast number, and resulted in a further decrease in cancellous bone volume compared with those in weight-bearing OVX rats. Programed administration of PTH had no effect on either radial or longitudinal bone growth in weight-bearing and hindlimb-unloaded OVX rats. PTH treatment had dramatic effects on selected cancellous bone measurements; PTH maintained cancellous bone volume in OVX weight-bearing rats and greatly reduced cancellous bone loss in OVX hindlimb-unloaded rats. In the latter animals, PTH treatment prevented the hindlimb unloading-induced reduction in trabecular thickness, but the hormone was ineffective in preventing either the increase in osteoclast number or the loss of trabecular plates. Importantly, PTH treatment increased the retention of a baseline flurochrome label, osteoblast number, and bone formation in the proximal tibial metaphysis regardless of the level of mechanical usage. These findings demonstrate that programed administration of PTH is effective in increasing osteoblast number and bone formation and has beneficial effects on bone volume in the absence of weight-bearing and gonadal hormones. We conclude that the actions of PTH on cancellous bone are independent of the level of mechanical usage.
Document ID
20040142232
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Turner, R. T.
(Mayo Foundation Rochester, Minnesota 55905, United States)
Evans, G. L.
Cavolina, J. M.
Halloran, B.
Morey-Holton, E.
Date Acquired
August 22, 2013
Publication Date
October 1, 1998
Publication Information
Publication: Endocrinology
Volume: 139
Issue: 10
ISSN: 0013-7227
Subject Category
Aerospace Medicine
Funding Number(s)
CONTRACT_GRANT: AR-35651
CONTRACT_GRANT: AR-41418
Distribution Limits
Public
Copyright
Other
Keywords
NASA Discipline Musculoskeletal
Non-NASA Center

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