The study concerns the role of PTH(1-34) during bone lesion repair. 3-month-old
male Sprague-Dawley rats, in which trans-cortical holes were drilled at femur middiaphysis,
were divided in groups with/without Teriparatide administration (40g/
Kg/day), and sacrificed at different times (10, 28, 45 days). In 2002 (1) we demonstrated
the occurrence of two successive bone forming processes during both skeletal
organogenesis and bone repair, i.e. static (SO) and dynamic (DO) osteogenesis: the
former (due to stationary osteoblasts, haphazardly grouped in cords) producing preliminary
bad quality trabecular bone, the latter (due to typical polarized osteoblasts
organized in ordered movable laminae) producing mechanically valid bone tissue.
In brief, the primary function of SO is to provide a rigid scaffold, containing osteocytes
(i.e. mechano-sensors), to DO-osteoblastic laminae; therefore, in DO mechanical
factors can play a crucial role in transduction of mechanical stresses into biological
signals. In the present work, histomorphometric analysis showed that, already after
10 days from drilling, notwithstanding the holes are temporarily filled by the same
amount of newly-formed trabecular bone (produced by SO) independently from the
treatment, the number of movable osteoblast laminae (typical of DO), covering the
trabecular surface, is statistically higher in animals submitted to PTH(1-34) administration
than in the control ones; this suggests that the mere effect of Teriparatide is
to anticipate the occurrence of dynamic osteogenesis involved in the production of
good quality bone more suitable to loading. These findings are also supported by the
higher values of microhardness as well as the more ordered-fibered texture (observed
by polarized light) in treated animals with respect to control ones that strongly indicates
the qualitative (instead of quantitative) effect of PTH (1-34) in improving bone
healing. The present investigation could be of crucial importance in further translational
clinical research in humans to define the best therapeutic strategies in recovering
skeletal lesions, particularly in terms of time of administration of PTH(1-34)