Submitted on March 25, 2003
Accepted on September 29, 2003
Blockade of the Sympathetic Nervous System Degrades Ligament in a Rat MCL Model
Kelley W Dwyer1, Paolo P Provenzano1, Peter Muir2, Wilmot B Valhmu3, and Ray Vanderby, Jr.1*
1 Orthopedic Research Laboratories, Department of Orthopedics and Rehabilitation, University of Wisconsin, Madison, WI, USA; Department of Biomedical Engineering, University of Wisconsin, Madison, WI, USA
2 Comparative Orthopaedic Research Laboratory, School of Veterinary Medicine, University of Wisconsin, Madison, WI, USA
3 Orthopedic Research Laboratories, Department of Orthopedics and Rehabilitation, University of Wisconsin, Madison, WI, USA
* To whom correspondence should be addressed. E-mail: vanderby{at}surgery.wisc.edu.
We hypothesize that blockade of the sympathetic nervous system degrades ligament. We tested this hypothesis in a rat medial collateral ligament (MCL) model. Fifteen animals were treated for ten days with the sympathetic chemotoxin guanethidine using osmotic pumps, while fifteen control rats received pumps containing saline. A reduction in plasma concentrations of norepinephrine in the guanethidine rats indicated a significant decrease in sympathetic nerve activity. Vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY) were decreased in MCLs from guanethidine animals as quantified by radioimmunoassays. Tissue vascularity was substantially increased in guanethidine MCLs, while mechanical properties were significantly decreased. Proteases, such as matrix metalloproteinases and cysteine proteases, play a major role in ligament degradation. The proteases MMP-13, cathepsin K, and tartrate-resistant acid phosphatase (TRAP) have collagenolytic acativity and have been shown in rat ligament tissues. To determine whether the degradation seen in this study was due to protease activity, we determined the expression of these enzymes in control and treated MCLs. Real time quantitative PCR revealed that guanethidine treatment increased expression of MMP-13 and cathepsin K mRNAs, although overall expression levels of MMP-13 and TRAP were relatively low. Histology also identified increases in TRAP and cathepsin K, but not MMP-13 in guanethidine treated tissues. Results support our hypothesis that blockade of the sympathetic nervous system substantially degrades ligament.
