Characterization of the enhanced paw edema response to carrageenan and dextran in 2,3,7,8-tetrachlorodibenzo-p-dioxin-treated rats.

Rats pretreated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, 10 micrograms/kg) are supersensitive to the edemagenic effects of carrageenan and dextran as indicated by the increased potency of these irritants in TCDD-treated animals compared to controls. This effect of TCDD was characterized using indomethacin, dexamethasone and a combination of cyproheptadine and pyrilamine as inhibitors of edema formation. Because TCDD increases the potency of carrageenan and dextran, it was necessary to select appropriate doses of the edemagenic irritants in order to evaluate the effect of edema inhibitors properly. At low and moderate irritant doses, TCDD-treated and control rats exhibited similar responses to inhibitory agents, suggesting that the mechanisms by which carrageenan and dextran produce edema involve the same mediators in control and TCDD-treated animals. The effect of TCDD on edema induced by bradykinin, histamine, prostaglandin E2 and serotonin, substances which are postulated endogenous mediators of carrageenan-, dextran- and/or compound 48/80-induced edemas, was also examined. Inasmuch as TCDD increased the edemagenic potency of bradykinin and histamine, but not that of prostaglandin E2 or serotonin, it was concluded that TCDD enhances carrageenan-, dextran- and compound 48/80-induced edema formation by augmenting the edemagenic activities of bradykinin and histamine. It is postulated that the mechanism of enhancement may involve TCDD-induced potentiation of the ability of bradykinin and histamine to stimulate phospholipase activity in vascular endothelial cells.