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- Title
α.
- Authors
McDonald, Stuart J.; Dooley, Philip C.; McDonald, Aaron C.; Djouma, Elvan; Schuijers, Johannes A.; Ward, Alex R.; Grills, Brian L.
- Abstract
Early, soft fracture callus that links fracture ends together is smooth muscle-like in nature. We aimed to determine if early fracture callus could be induced to contract and relax ex vivo by similar pathways to smooth muscle, that is, contraction via α adrenergic receptor (αAR) activation with phenylephrine (PE) and relaxation via β adrenergic receptor (βAR) stimulation with terbutaline. A sensitive force transducer quantified 7 day rat rib fracture callus responses in modified Krebs-Henseliet (KH) solutions. Unfractured ribs along with 7, 14, and 21 day fracture calluses were analyzed for both αAR and βAR gene expression using qPCR, whilst 7 day fracture callus was examined via immunohistochemistry for both αAR and βAR- immunoreactivity. In 7 day callus, PE (10 M) significantly induced an increase in force that was greater than passive force generated in calcium-free KH ( n = 8, mean 51% increase, 95% CI: 26-76%). PE-induced contractions in calluses were attenuated by the αAR antagonist, prazosin (10 M; n = 7, mean 5% increase, 95% CI: 2-11%). Terbutaline did not relax callus. Gene expression of αARs was constant throughout fracture healing; however, βAR expression was down-regulated at 7 days compared to unfractured rib ( p < 0.01). Furthermore, osteoprogenitor cells of early fibrous callus displayed considerable αAR-like immunoreactivity but not βAR-like immunoreactivity. Here, we demonstrate for the first time that early fracture callus can be pharmacologically induced to contract. We propose that increased concentrations of αAR agonists such as noradrenaline may tonically contract callus in vivo to promote osteogenesis. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29:740-745, 2011
- Subjects
ADRENERGIC receptors; TREATMENT of fractures; RIB injuries; SMOOTH muscle; MUSCLE contraction
- Publication
Journal of Orthopaedic Research, 2011, Vol 29, Issue 5, p740
- ISSN
0736-0266
- Publication type
Article
- DOI
10.1002/jor.21302