Seasonal variation in drug action and animal responses in models of inflammation.

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.