INFLAMMATOGENIC PROPERTIES OF NUCLEUS PULPOSUS

Study Design. The inflammatogenic properties of nucleus pulposus were assessed in two experimental models previously used for screening of inflammatogenic properties of other substances. This study was performed to assess the inflammatogenic properties of nucleus pulposus in models previously screened for other substances. Summary of Background Data. Previous experimental studies, as well as clinical observations, have indicated that inflammatory mechanisms may constitute an important pathogenetic component in sciatica due to herniation of the nucleus pulposus. Methods. In the first experimental series, autologous nucleus pulposus and retroperitoneal fat were placed in perforated titanium chambers, which were placed subcutaneously in pigs, together with an empty chamber as sham. After 7 days, the number of leukocytes in the chambers was determined. In the second experimental series, the microvascular reactions were studied by vital microscopy of the hamster cheek-pouch after local injections of suspensions of homologous nucleus pulposus and homologous subcutaneous fat. Macromolecular extravascular leakage was studied by fluorescence microscopy using FITC-dextran as a tracer. Results. The leukocyte ratio between fat control and sham was 0.9 +/- 0.6 and between nucleus pulposus and sham 2.4 +/- 0.7. The nucleus pulposus thus attracted significantly more leukocytes than fat. Injection of nucleus pulposus suspension induced thrombosis formation and pronounced leakages of macromolecules in a majority of the injection sites. However, injection of vehicle and fat suspension in the cheek-pouch only resulted in minor vital microscopic changes. Conclusions. Nucleus pulposus demonstrated inflammatogenic properties as indicated by leukotaxis and an increase of vascular permeability. It was not clear, however, if these reactions were induced by substances from the nucleus pulposus per se or from substances being liberated from other tissues as a response to an interaction with components of the nucleus pulposus.