Morphology of the bentonite and kaolin-induced rat-paw oedemas

The bentonite and kaolin oedemas were simultaneously induced in the rat hind paws and their courses and morphological patterns were observed under the conditions of the same biological background. Gross examination has confirmed the former experience that the kaolin oedema has a more pronounced acute phase (maximum after five to seven hours) followed by subsequent spontaneous regression of the oedema, while the bentonite oedema has its acute phase less pronounced, attains its peak only on the second day, maintaining this same size over several weeks without substantial changes. The courses of the two oedemas were in correlation with the results of histological evaluation (oedematous exudation, polymorphonuclear and mononuclear infiltration and the phagocytic activity of the latter). Resorption of kaolin in the newly-developed non-specific granulation tissue was much faster than that of bentonite (after about three weeks, while bentonite was not resorbed even after six weeks). Further, pharmacological and histological examination was performed of the effects on the bentonite oedema of sodium salicylate and Prednisone during the first 24 hours. Both substances suppressed the oedema, sodium salicylate delayed both polymorphonuclear and mononuclear infiltration, Prednisone delayed only mononuclear infiltration. The presence of mononuclear population was confirmed also by means of the positive activity of non-specific esterase and the negative activity of alkaline phosphatase. The bentonite rat-paw oedema has thus been proved to be a suitable model of inflammatory reaction for testing anti-inflammatory drugs not only in short-term (acute) tests, but also in long-term ones, where it yields a uniform picture of non-specific foreign-body low-turnover granuloma.