Exogenously Administered Substance P and Neutral Endopeptidase Inhibitors Stimulate Fibroblast Proliferation, Angiogenesis and Collagen Organization during Achilles Tendon Healing

Background: In the last few years much research has been conducted in methods to promote tendon healing. The aim of this study was to determine if the healing process after operative repair of rat Achilles tendons could be stimulated by the paratendinous injection of a sensory peptide, substance P (SP). Methods: Ninety-six male Sprague-Dawley rats were randomly allocated to four groups: (I) control buffer injections, (II) injections of SP 10−6 mol/kg body weight combined with a carrier, (III) injections of SP 10−8 mol/kg BW with the carrier, and (IV) injections with the carrier only (thiorphan 1 μmol/kg BW and captopril 30 μmol/kg BW, both neutral endopeptidase inhibitors). The influence on tissue repair was determined from the histologic measurement of fibroblast proliferation, angiogenesis, and collagen organization. On days 7, 14, 28 and 42, animals were sacrificed and histologic evaluations were performed on the injured Achilles tendon constructs.Results: The two groups subjected to SP injections show...