title: Modifications of bone and connective tissue after orthostatic bedrest.
abstract: Eight male volunteers were submitted to a 6-week anti-orthostatic bedrest trial followed by a 1-month reambulation period. We prospectively monitored whole-body composition by dual-energy X-ray absorptiometry, bone and connective tissue metabolism by biochemical markers and calcium regulating hormones by 1-84 parathyroid hormone and 1,25-dihydroxyvitamin D(3). Bone mineral density (BMD) did not vary significantly; however, a trend toward an increase in head BMD and a decrease in trunk, lumbar vertebrae and lower limb BMD was observed. A decrease in the lower limb lean content occurred by day 27 and was maximum by day 42 after the beginning of bedrest; it normalized by day 30 after bedrest. The serum levels of both osteocalcin and C-terminal crosslinked telopeptide of type I collagen increased as a consequence of bedrest. A slight increase in the serum levels of the N-terminal propeptide of type III collagen, a marker of connective tissue metabolism, was observed during the bedrest period. Except for the C-terminal extension propeptide of type I collagen, all markers decreased to baseline pre-immobilization levels during the 1-month recovery phase. Serum PTH and 1,25-dihydroxyvitamin D(3) levels were low during the bedrest period and rose during the reambulation phase. These results seem to reflect early changes in bone and connective tissue metabolism as a result of bedrest unloading, but their order of magnitude remains moderate, thus emphasizing the necessity to perform longer-duration trials.
authors.affiliation: Department of Clinical Neurosciences and Dermatology, Clinic of Rehabilitation, University Hospital, Geneva, Switzerland.
authors.forename: D
authors.initials: D
authors.lastname: Uebelhart
authors.forename: J
authors.initials: J
authors.lastname: Bernard
authors.forename: D J
authors.initials: DJ
authors.lastname: Hartmann
authors.forename: L
authors.initials: L
authors.lastname: Moro
authors.forename: M
authors.initials: M
authors.lastname: Roth
authors.forename: B
authors.initials: B
authors.lastname: Uebelhart
authors.forename: M
authors.initials: M
authors.lastname: Rehailia
authors.forename: G
authors.initials: G
authors.lastname: Mauco
authors.forename: D A
authors.initials: DA
authors.lastname: Schmitt
authors.forename: C
authors.initials: C
authors.lastname: Alexandre
authors.forename: L
authors.initials: L
authors.lastname: Vico
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods; D000328:Adult; D001510:Bed Rest / Q000009:adverse effects*; D015415:Biomarkers; D001823:Body Composition / Q000502:physiology*; D015519:Bone Density / Q000502:physiology; D001846:Bone Development; D001842:Bone and Bones / Q000502:physiology*; D003238:Connective Tissue / Q000502:physiology*; D006801:Humans; D008297:Male; D011446:Prospective Studies
chemical_list: D015415:Biomarkers