C. Ejersted et al., PARATHYROID-HORMONE-(1-34) INCREASES VERTEBRAL BONE MASS, COMPRESSIVESTRENGTH, AND QUALITY IN OLD RATS, Bone, 17(6), 1995, pp. 507-511
Human parathyroid hormone 1-34 (PTH) exerts an anabolic effect on bone
in younger rats, The aim of the present study was to examine the effe
ct of PTH on vertebral bone in 2-year-old male rats, The rats were tre
ated with daily injections of 15 nmol/kg PTH or vehicle (V) for 56 day
s, Tetracycline and calcein were injected on day 15 and day 40 of the
treatment period, respectively, The PTH treatment did not influence th
e body weights of the rats, the volumes of whole vertebra, or the vert
ebral body heights, However, the PTH treatment induced profound change
s in the bone structure, Histomorphometric analyses of the vertebral b
odies (L-6) revealed an approximate doubling of the cancellous bone vo
lume after PTH treatment from 24.6 +/- 1.3% to 54.9 +/- 2.0% (p < 0.00
1) as well as a doubling of the trabecular thickness while the bone su
rface/bone volume decreased by 60%. PTH treatment also increased bone
formation as indicated by an increase in mineral apposition rate (from
0.42 +/- 0.01 to 0.89 +/- 0.01 mu m/day, p < 0.01), increased mineral
izing surface (from 7.8 +/- 1.4 to 43.8 +/- 1.9%, p < 0.01) and an inc
rease in both volume-related and surface-related bone formation rates
(5 and 11 times, respectively), The biomechanical properties were anal
yzed using standardized bone specimens from the vertebral bodies of L-
4 by applying cranial-caudal compression in a materials testing machin
e, The PTH treatment induced a substantial increase in the strength of
the vertebral body: ultimate load increased by 66%, ultimate stiffnes
s by 47%, and energy absorption by 98%. The increase in vertebral body
strength was also evident after normalizing the parameters to the cro
ss sectional area and the ash content of the vertebral body specimens,
PTH treatment increased ultimate stress from 26 +/- 3 to 44 +/- 3 N p
er mm(2) (p < 0.01) and increased ultimate load normalized to ash cont
ent per mm specimen height from 59 +/- 4 to 72 +/- 4 N (mm/mg) (p < 0.
05), The PTH treatment induced an increase in dry defatted bone densit
y and ash density of both the vertebral body specimen (L-4) and the wh
ole vertebra (L-5). In conclusion, PTH showed a remarkable ability to
stimulate bone formation in the vertebral body of old rats, Furthermor
e, the biomechanical analysis revealed an enhanced compressive bone st
rength, even after correction for the increased bone mass, indicating
an improved bone quality after the PTH treatment.