Progressive foot swelling in BUF rats. A new animal model for screening of anti-inflammatory and anti-rheumatic drugs.

Buffalo rats of a low adjuvant-arthritis responder strain demonstrate a continually increasing swelling in the hind foot inoculated with mycobacterial adjuvant, characterized by extensive panostitis, new bone formation and long-delayed bony calcification. A rapid regression of foot swelling was produced by a three-day course of therapy with indomethacin (1 mg/kg) or with dexamethasone (0.1 mg/kg), but a definite rebound was followed soon after termination of the therapy. This recurrent episode occurred repeatedly in the second and third therapeutic trials with the anti-inflammatory drugs in the same animals. The 5 days treatment with either levamisole (5 mg/kg) or cyclophosphamide (5 mg/kg) prevented further increase in the swelling for a long time period after withdrawal of the drug, and enhanced bone mineralization.