During the summer months, aspirin was relatively ineffective in rats in suppressing leucocyte migration both into the pleural space inflamed by carrageenan and into inert sponges implanted subcutaneously. At this time period, rats were insensitive to intravenous histamine and relatively insensitive to anaphylactic shock, and survival rates after traumatic or tourniquet shock have also been reported to be at peak values. The cause of this resistance has still to be found, though hormonal activation may play a major role.
Carrageenan injected subcutaneously into one hindpaw of the rat produces an anaphylactoid reaction which prevents the same paw responding to a second dose 14 days later but does not alter the response to dextran. However, dextran does not modify the response of the hindpaw to a subsequent dose of either dextran or carrageenan 14 days later. When using these models of inflammation for testing the anti-inflammatory activity of drugs, valuable extra information may be gained by adopting the cross-over technique and using both paws of each animal.
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