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Formulations of a number of steroids were evaluated after topical application in a reversed passive Arthus test (RPA) in rabbits. Four 21-chlorosteroids in the same cream base were investigated. The preparations of SQ 18,566 (halcinonide) and SQ 20,811 showed anti-edema activity, but those of SQ 15,361 and SQ 20,589 were less active. Ointment formulations of halcinonide also reduced edema in the RPA. These results, coupled with previously reported clinical data, suggest that the RPA might be utilized to distinguish good from poor formulations of anti-inflammatory steroids prior to screening tests or clinical trials in humans.

Synovitis was induced in rabbits sensitized to bovine serum albumin (BSA) by a modification of the method of Dumonde and Glynn. Agents were administered starting on the day of initial BSA joint challenge and every weekday (14-17 doses) for 17 to 21 day periods. Synovial tissues were then excised and evaluated either (1) histologically for inflammatory cell infiltration, or (2) both histologically and for total IgG, anti-BSA, and beta-glucuronidase levels in homogenates of portions of the same tissues. By the intraperitoneal and oral routes, methylprednisolone (1 mg/kg/day), azathioprine (25-40 mg/kg/day) and cyclophosphamide (10 mg/kg/day) produced significantly decreases of 40-100% in some or all of the parameters measured. Non-steroidal anti-inflammatory drugs, including phenylbutazone, ibuprofen and acetylsalicylic acid at oral doses of 75 or 100 mg/kg/day, were ineffective as were colchicine at 1 mg/kg/day and indomethacin at 5 mg/kg/day. Thus, as we have measured it, this model of rheumatoid arthritis is not affected by those agents considered to be of limited effectiveness in this chronic disease, but is ameliorated by corticoids and some slow acting agents.

The immune complex-induced reversed passive Arthus (RPA) reaction in the rabbit has been investigated as a screening test for detecting anti-inflammatory agents potentially more effective in the treatment of rheumatoid arthritis than those presently available. RPA lesions, characterized by edema, erythema, and hemorrhage, were elicited by intravenous injections of bovine serum albumin (BSA) followed by intradermal injections of rabbit anti-BSA antiserum. The anti-edema activities of compounds (mg quantities required for testing) were evaluated after their administration by the intradermal route (compounds admixed with antiserum) as well as by the intraperitoneal route. Of 14 reference anti-inflammatory agents tested by the intradermal screening procedure, only aurothioglucose and chloroquine were inactive. Other pharmacologically active compounds (e.g. antihistamines, anti-complement agents, cytotoxic-immunosuppressives) were also evaluated after their intradermal administration. Protoporphyrin, phloretin, and hexadimethrine bromide (Polybrene) were active. When whole antiserum, or the antibody fraction of the serum, was used to eliminate nonspecific edema, intraperitoneally administered reference agents were found to be effective in the RPA test.

In order to better define antiinflammatory activity in new agents, a test was devised utilizing both carrageenan induced paw edema and the reversed passive Arthus reaction in the same animal. The model of carrageenan induced rat paw edema is a standard laboratory assay used to predict classical "aspirin-like" antiinflammatory molecules. The reversed passive cutaneous Arthus reaction involves precipitating antigen-antibody complexes, complement and infiltrating polymorphonuclear leukocytes (PMN's) and can be used to identify agents that affect one or more of these factors specifically. Antiinflammatory compounds were given orally one hour prior to the administration of carrageenan and goat anti-rat serum. Comparisons were made between several non-steroidal compounds and the steroid hydrocortisone. All of the compounds tested gave good carrageenan activity, but only hydrocortisone produced significant Arthus lesion inhibition in this assay.

Immune synovitis in rabbits was investigated as a potential in vivo model for evaluating new antiinflammatory agents. Antigen-induced increases in knee width as well as beta-glucuronidase and acid phosphatase activities in exudates were observed. Histologically, polymorphonuclear leukocytes appeared within hours in synovial tissues and reached maximum infiltration at about 24 hours. Subsequently, mononuclear cells, including plasma cells, appeared. The 6-hour Arthus-like phase of synovitis can be depressed by some antiinflammatory agents, colchicine and steroids being particularly effective. It is suggested that this model can be utilized to define potentially more effective antiinflammatory drugs.