Abstracts Posters SICOT-SOF meeting Gothenburg 2010 _2_

Poster
Topic: Trauma - Systemic
Abstract number: 26454
NEURONAL FACTORS SUBSTANCE P AND NEUROPEPTIDE Y IN FRACTURE
REPAIR
Paul ACKERMANN, Jian LI, Mahmood AHMED, Jonas BERGSTRöM, Andre
STARK, Andris KREICBERG
Karolinska Institutet, Stockholm (SWEDEN)
The occurrence and role of local neuronal factors, substance P (SP) and
neuropeptide Y (NPY), in fracture healing is not known. The present study
investigated the correlation between bone turn-over and side-specific presence of SP
and NPY in angulated versus straight fracture repair. Tibial fractures in Sprague-
Dawley rats were fixed with intramedullary pins in straight alignment and anterior
angulation, respectively resulting in a convex and concave side under different load.
Fracture repair was assessed by radiography, histology, and semi-quantitative
immunohistochemistry between days 3-84 post-fracture.Abundant SP/NPY-nerve
ingrowth was observed in the fracture callus reaching a side-symmetrical peak at day
21-35 in straight fracture. The angulated fracture exhibited during days 1-21
(inflammation/regeneration), a higher SP/NPY-density on the concave bone forming
side (345% increase in bone-thickness) compared to the convex side (21%) (p<
0.05). During remodeling, days 21-84, a side-symmetrical disappearance of SP/NPYfibers
was seen in straight fracture. Remodelling in the angulated fracture, however,
exhibited higher SP/NPY-density on the convex bone resorbing compared to the
concave side (p< 0.05). Our study suggests that neuromediators SP/NPY during
early fracture repair stimulate bone formation, while during remodeling increased
SP/NPY in unloaded areas at the fracture site may stimulate resorption. It may prove
that unloading during fracture remodeling in addition to increase the occurrence of
SP/NPY leads to up-regulation of their receptors on bone-resorbing osteoclasts.
These findings may explain contradictory observations that SP in vitro timedependently
could stimulate both formation and resorption of bone.
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