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Role of Growth Hormone, Exercise and Serum Phosphorus in Unloaded Bone of Young RatsGrowth hormone, known to be stimulated by exercise, is suppressed in rats after space flight and in a ground-based model in which the hind-limbs are unloaded (S). To determine the role of GH in the osteopenia of unloaded bones of S rats, young males were treated with GH combined with insulin-like growth factor-1 (IGF-1), a peptide that mediates the local actions of the hormone. 200 g rats, hypophysectomized (hypox) 17 d earlier, were treated with 1 mg/kg/d GH/IGF-1 (H) or saline (C) in 3 divided daily doses x10 d. Hind-limb bones were unloaded (S), ambulated (A) or exercised (X) by climbing a ladder while carrying a weight. Growth was monitored daily. Tibial growth plate (Tepi) was measured with a micrometer, and femoral (F) area, length, and mineral content (BMC) by DEXA. Parameters of calcium metabolism were measured by autoanalyzer and calciotropic hormones by radioimmunoassay. F bone density, g/square cm, (BMD) or BW were not affected by S in Hypox. However, FBMD was lower in S+H than A+H (p is less than 0.002) and H stimulated whole body growth in S (5.2 g/d) and SX (5.6 g/d) to a lesser extent than in A (6.6 g/d) (p is less than 0.05). Adjusted for BW, Tepi showed the greatest increase in S+H+X (64%), the next highest increase in S+H (50%) and no change in S+X. F area, length and BMC/100 g BW were lower in all H groups than respective C's. By multiple regression analysis, serum phosphorus (Pi) which correlated with Tepi (r = 0.88, p is less than 0.001) and was inversely related to FBMC (r = -0.68, p is less than 0.001) proved to be the most significant determinant of BMC. This illustrates the dependence of osteopenia in S on GH, the maximizing effect of X for epiphyseal growth and the major role of Pi metabolism on BMC in weight bearing bone during growth.
Document ID
20020010243
Document Type
Conference Paper
Authors
Arnnaud, Sara B. (NASA Ames Research Center Moffett Field, CA United States)
Harper, J. S. (NASA Ames Research Center Moffett Field, CA United States)
Gosselink, K. L. (NASA Ames Research Center Moffett Field, CA United States)
Navidi, M. (NASA Ames Research Center Moffett Field, CA United States)
Fung, P. (NASA Ames Research Center Moffett Field, CA United States)
Grindeland, R. E. (NASA Ames Research Center Moffett Field, CA United States)
Wade, Charles E.
Date Acquired
August 20, 2013
Publication Date
January 1, 1994
Subject Category
Life Sciences (General)
Meeting Information
Aerospace Medical Association Meeting(Anaheim, CA)
Funding Number(s)
PROJECT: RTOP 199-26-12-02
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.