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The effect of aging on the skeletal response to intermittent treatment with parathyroid hormone.
- Knopp E, Troiano N, Bouxsein M, Sun BH, Lostritto K, Gundberg C, Dziura J, Insogna K
Endocrinology. 2005 Apr;146(4):1983-90. Epub 2004 Dec 23.
Little is known about the modifying effects of age on the skeletal
response
to intermittent treatment with PTH. We therefore compared the response
of 63 aged
(18 month old) and 61 young-adult (3 month old) C57BL/6 mice to 4 wk of daily sc injections of either vehicle
or h(1-34)PTH at a dose of 95 ng/g body weight. The increase in total body bone mineral density (BMD), compared with vehicle-treated animals, was similar in aged
and young-adult mice (+5.6 vs. +6.3%). Aged
animals demonstrated a greater increase in spinal BMD than their younger counterparts (+12.0 vs. +5.1%, P = 0.01; absolute increment:
57 x 10(-4) vs. 28 x 10(-4) g/cm(2)). Microcomputed tomography
analyses in a subset of the vertebrae showed a trend toward higher L5 trabecular bone
volume fraction in the PTH-treated aged
animals (+40.2 vs. +19.6%). Vertebral
histomorphometry demonstrated a greater PTH-induced increase in osteoblast
number in aged
vs. young-adult animals (694 vs. 396 cells/mm(2)). In contrast, in the femur
the PTH-induced increase in BMD tended to be greater in the young-adult than the aged
animals, although this did not reach statistical significance (8.1 vs. 4.2%). The numbers of osteoblast
progenitors and mineralizing colonies in cultured
marrow
were unaffected by PTH treatment in either group. We conclude that aging
differentially impacts the regional
skeletal
response
to PTH such that the increase in BMD in the spine is augmented, whereas that in the femur
is unaffected. Effects on osteoblast
progenitor recruitment
do not seem to be the basis for these changes.
This abstract at PubMed.