AJP - Endocrinology and Metabolism, Vol 259, Issue 5 E715-E722, Copyright © 1990 by American Physiological Society
Different responses of trabecular and cortical bone to 1,25(OH)2D3 infusion
D. D. Bikle, B. P. Halloran, C. McGalliard-Cone and E. Morey-Holton
Veterans Administration Medical Center, San Francisco, California 94121.
Previous studies regarding the effects of 1,25-dihydroxyvitamin D3
[1,25(OH)2D3] on bone have suggested that 1,25(OH)2D3 increases bone mass
and calcium. Many of these studies have focused on trabecular or total bone
without examining cortical bone per se. To determine whether the response
of trabecular bone to 1,25(OH)2D3 differed from the response of cortical
bone, we infused 1,25(OH)2D3 into rats and examined bone mass, 45Ca
accumulation, and the density distribution of bone particles (as a measure
of bone maturation) in both the proximal tibia and shaft. In the proximal
tibia 1,25(OH)2D3 decreased 45Ca accumulation, yet increased bone mass and
shifted the particle distribution to more mineralized fractions. In the
shaft there was a redistribution of bone to less mineralized fractions that
was not accompanied by a change in total bone mass or a decrease in 45Ca
accumulation. Thus 1,25(OH)2D3 may retard bone maturation and
mineralization throughout the tibia, but this effect in the proximal tibia
appears to be overshadowed by a reduction in bone resorption resulting in
an accumulation of well-mineralized bone in that region. Bone resorption,
however, was not measured directly. The net result is an increase in bone
mass and density of trabecular bone not seen in cortical bone.
