Relationship between oedema and plasma exudation in rat paw carrageenin inflammation.

High (500 microgram) and low (100 microgram) doses of carrageenin produced different temporal extravasation of plasma protein when injected into the rat paw. High doses caused a continuous extravasation parallel to the oedema increase. With low doses, main exudation occurred during the first 2 h and was minimal when the oedema was maximal (4th hour). Pre-treatment with indomethacin (2 mg/kg/i.p.) was effective in reducing oedema and protein extravasation for both doses of carrageenin. Indomethacin given 2 h after carrageenin had no effect upon the oedema caused by the low doses, but was effective with the high doses of carrageenin. The anti-oedematogenic effect of a non-steroid anti-inflammatory agent, such as indomethacin, was related to its effect upon plasma exudation, i.e. the agent was effective when there was a correlation between increment of oedema and plasma extravasation. The continuously increased plasma extravasation indicated the continuous presence of an active damaging stimulus. Our results explain several apparently contradictory observations reported in the literature.