Inhibitory effects of clonidine on edema formation after thermal injury in mice and rats

Clonidine 1 mg/kg ip given before thermal injury significantly inhibited the edema formation in mice and rats during the early stage of burn. Clonidine 0.1 mg/kg ip gave no such effect, but it became effective after being administrated via icv. The inhibitory effects of clonidine on edema formation were abolished by pretreatment with yohimbine 5 mg/kg ip, but not with prazosin 10 mg/kg ip. The tracing by 113mIn labelled transferrin demonstrated that clonidine decreased the capillary permeability in burned tissues 1 h after burn. When clonidine 1 mg/kg was given ip to the rats 20 min before burn, it lowered the level of lipoperoxide in the serum 2 h after burn. These results suggest that the inhibitory effects of clonidine on edema formation is most probably due to the depression of sympathetic activity via alpha 2 receptor during thermal injury.