An experimental study of the neurogenic and the immunological contribution to "tennis elbow" in rats

In the present study the content of substance P (SP)-, neurokinin A (NKA)-, calcitonin gene-related peptide (CGRP)- and neuropeptide Y (NPY)-like immunoreactivity (-LI) was measured in rats cerebrospinal fluid (CSF), plasma and perfusates (PF) from both elbow enthesis during acute inflammation. Either substance P, SP, (10-5 M, 0.01 ml) or human recombinant interleukin-1 alpha (hrIl-1 alpha, 0.01 ml) were injected into the right enthesis of the extensor carpi radialis brevis (ECRB). The left ECRB and both ECRBs of control rats, were injected with 0.01 ml saline. Samples of CSF, plasma and PF from both ECRBs were obtained at 2, 6, and 24 h following injection and neuropeptide-LI was analysed by specific radioimmunoassays. Neuropeptide-LI was compared with control values and between the treated groups. In both treated groups NKA- and CGRP-LI was increased in CSF and NKA-LI decreased in plasma, while CGRP- and NPY-LI were raised to a similarly significant degree in the enthesis of the ECRB. SP-LI was increased in ECRB PF in comparison with controls and NKA-LI levels were higher in the hrIl-1 alpha group both in comparison with controls and between treated groups. In summary an unilateral injection of either SP or hrIl-1 alpha into the enthesis of the ECRB of the rat showed a similar influence at 2, 6, and 24 h following injection. The most pronounced changes in neuropeptide-LI occurred in the ECRB PF of both treated groups.