Tendon healing is characterized mostly by slow rehabilitation and, as in tendinopathy, aberrant, protracted sensory nerve ingrowth. This study investigated whether administration of the sensory neuropeptide substance P (SP) could enhance healing and modulate sensory nerve plasticity after Achilles tendon rupture. Fifty-four male Sprague-Dawley rats were allocated to three groups, all receiving six daily injections post-rupture of; (1) SP (10(-6) mol/kg body weight)+endopeptidase inhibitors captopril and thiorphan, (2) captopril/thiorphan only and (3) saline control. At 1, 3 and 6 weeks post-rupture tendon healing was evaluated by assessments of fibroblast proliferation, collagen III-LI (like) occurrence, diameter of newly organized collagen and sensory nerve fiber ingrowth. At 1 week, the SP-treated group exhibited increased occurrence of collagen III-LI (P=0.03) and of organized collagen (P=0.04) compared with control. At 3 weeks, the SP group notably displayed reduced SP-nerve fiber ingrowth (P=0.02), and higher fibroblast density (P=0.004). Both the SP and captopril/thiorphan groups demonstrated increase in collagen fiber organization compared with control (P=0.02 and 0.004, respectively). At 6 weeks, no significant differences were observed between the groups. SP supply in tendon repair promotes early tissue proliferation and regulation of endogenous sensory nerve ingrowth, suggesting implications for novel treatment in tendinopathy.
© 2010 John Wiley & Sons A/S.