THE ROLE OF STEROIDS AND THEIR EFFECTS ON PHOSPHOLIPASE-A2 - AN ANIMAL-MODEL OF RADICULOPATHY

Study Design. The possible role of phospholipase A2 in an animal model for lumbar radiculopathy and mechanisms of epidural steroid injection s were studied. Objectives. To clarify the pathophysiologic mechanism of the recently proved animal model for lumbar radiculopathy and to ch aracterize further the mechanisms of action of steroids. Summary of Ba ckground Data. There have been several reported animal models of perip heral neuropathy. Recently an animal model that shows reliable behavio ral and neurochemical changes was proposed, and epidural steroid injec tions in this model were effective in the reduction of thermal hyperal gesia and allodynia. Method. In a behavioral study, 24 rats were divid ed into 4 groups: Group I, loose ligature of the left L4 and L5 nerve roots with 4-0 chromic gut sutures and an epidural injection of 0.1 mL of saline at 3 days after surgery; Group II, same as Group I but with an epidural injection of 0.1 mt of betamethasone on the day before th e operation; Group III, same as Group Il except injection at 1 day aft er surgery; Group IV, same as Group It except injection at 3 days afte r surgery. To test the phospholipase A2 activity in the nerve roots an d dorsal root ganglia after the operation, eight rats were killed at g iven intervals. Analysis of variance techniques were used to test beha vioral pattern changes and phospholipase A2 activity across time in ea ch group. Results. Thermal hyperalgesia reached its maximal point at 3 weeks after surgery in Group I, but in steroid injection groups, the recovery from hyperalgesia was faster than in Group I. However, there was no significant difference in recovery time among steroid injection groups. The level of phospholipase A2 activity was at its maximum at 1 week after surgery in Groups I and IV. It showed a steady reduction in the steroid group, whereas it remained relatively high and dropped rapidly after 3 weeks in the saline-treated group, and returned to the level of a normal nerve root at 6-weeks after surgery. Conclusion. Th ese-results suggest that the: behavioral pattern changes observed in t he irritated nerve root model are caused in part by a high level of ph ospholipase A2 activity initiated by inflammation, and that the mechan ism of action of epidural steroid injection in this model is inhibitio n of phospholipase A2 activity.