Comparative morphological studies on adjuvant arthritis induced in the extremities of rats, mice, and golden hamsters by intracutaneous injection of Freund's complete adjuvant.

Forty rats, 60 mice, and 60 golden hamsters were administered complete Freund's adjuvant by intracutaneous injections in an attempt to produce the clinical picture of arthritis. 90% of the rats, 25% of the mice, and 40% of the golden hamsters developed swollen extremities similar to those observed in rats affected by adjuvant arthritis. 12 animals of each of the 3 species included in this investigation, which showed macroscopically visible swellings of their extremities, were used for comparative histological studies in order to find out whether the swellings of the extremities of mice and golden hamsters are real inflammations of joints and identical with rat adjuvant arthritis. The animals were killed, at 4-day intervals, between the 8th and the 44th days from administration of the adjuvant. Whereas rats showed the full clinical picture of adjuvant arthritis, mice and hamsters exhibited only inflammatory pedal edema without florid arthritis. The involvement of the joints was confined to a minor focal reaction of the synovial membranes of small individual joints. The results obtained support the view of rat adjuvant arthritis being a species-specific reaction rather than corresponding to a species-dependent, universal principle of reaction.