Adjuvant polyarthritis in rats: is this a satisfactory model for screening anti-arthritic drugs?

The pathological and biochemical features of the polyarthritis in rats induced by Freund's adjuvant are briefly reviewed. The object of this is to highlight recent studies that provide a basis for specifically improving procedures employed in screening the activity and mode of action of anti-inflammatory/antiarthritic drugs--especially those with possible disease modifying activity. Current screening procedures involve the simple measurement of hind-paw or joint swelling. This may not reflect the extent of degradation or systemic changes in arthritis. It is suggested that it is possible to more precisely measure the extent of joint degradation by the following: (1) X-ray monitoring of joints afflicted with the disease, (2) Histological and morphological examination (the latter in alkali cleared--Alizarin stained preparations) of hindlimbs, (3) Quantitative histoenzymic and biochemical analysis of degradative enzymes and inflammatory mediators. Additional to this specific immunological and systemic (blood, liver) changes should be measured in primary screening in recognition that arthritis is a disease not only of joints but involving the immune, hepatic and possibly other organ systems and that these systemic components clearly have effects on joints. Only by a combined analysis of both local joint and systemic changes during drug treatment will it be possible to discriminate new drugs with disease-modifying activity.