Neural stimulation does not mediate attenuated vascular response in ACL‐deficient knees: Potential role of local inflammatory mediators

Chronic inflammation associated with osteoarthritis (OA) alters normal responses and modifies the functionality of the articular vasculature. Altered responsiveness of the vasculature may be due to excessive neural activity associated with chronic pain and inflammation, or from the production of inflammatory mediators which induce vasodilation. Using laser speckle perfusion imaging (LSPI), blood flow to the medial collateral ligament (MCL) of adult rabbits was measured in denervated ACL transected knees (n = 6) and compared to unoperated control (n = 6) and 6‐week anterial cruciate ligament (ACL)‐transected knees (n = 6). Phenylephrine and neuropeptide Y were applied to the MCL vasculature in topical boluses of 100 µL (dose range 10^?14 to 10^?8 mol and 10^?14 to 10^?9 mol, respectively). Denervation diminished vasoconstrictive responsiveness to phenylephrine compared to both control and ACL‐transected knees. Denervation minimally enhanced vascular responses to neuropeptide Y (NPY) compared to ACL deficiency alone, which nevertheless remained significantly diminished from control responses. To evaluate the potential role of inflammatory dilators in the diminished contractile responses, phenylephrine was coadministered with histamine, substance P, and prostaglandin E₂. High‐dose histamine, and low‐dose substance P and PGE₂ were able to inhibit contractile responses in the MCL of control knees. Excessive neural input does not mediate diminished vasoconstrictive responses in the ACL transected knee; inflammatory mediators may play a role in the deficient vascular responsiveness of the ACL transected knee. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:83–88, 2010