AJP - Endocrinology and Metabolism, Vol 263, Issue 1 E107-E114, Copyright © 1992 by American Physiological Society
Osteocalcin and its message: relationship to bone histology in magnesium-deprived rats
T. O. Carpenter, S. J. Mackowiak, N. Troiano and C. M. Gundberg
Department of Pediatrics, Yale University School of Medicine, New Haven, Connecticut 06510.
These studies examine effects of brief Mg deprivation on bone
histomorphometry and on secretion and synthesis of the specific osteoblast
product, osteocalcin. Osteocalcin mRNA was determined in calvaria-derived
cells and was correlated to circulating concentrations of the protein after
8 days of Mg deprivation. Circulating osteocalcin was decreased in
Mg-deprived rats when compared with pair-fed normal rats after 8 days of Mg
deprivation, with no significant changes in calcium or
1,25-dihydroxyvitamin D [1,25(OH)2D]. Serial sampling demonstrated a
difference in osteocalcin levels by 2 days of Mg deprivation, before any
changes in circulating calcium or parathyroid hormone were present.
Although circulating osteocalcin is decreased in Mg-deprived animals,
levels can be stimulated with 1,25(OH)2D3. Osteocalcin mRNA is reduced
after Mg deprivation, suggesting that low circulating levels are due, at
least in part, to reduced osteocalcin synthesis. Mg-deprived rats had
diminished bone volume and abnormal histological features consistent with
disorganized and chaotic bone remodeling. These findings indicate that
low-Mg intake during growth can alter the quality and quantity of bone and
suggest that Mg deprivation may contribute to the development of
osteoporosis.
