ABSTRACT
Objective To investigate the effects of clonidine on the expression of myocardial ? subunit of inhibitory G protein (Gi?) in severely scalded rats and the mechanisms. Methods A scald model of 30% total body surface area Ⅲdegree burn on the back of rats was established. The basal and Gpp (NH) p, forsklin stimulated activity of adenylate cyclase (AC), and Gi? in cardiac myocytes were determined by indirect enzyme radiochemical assay and Western blotting, respectively. Results Clonidine at the dosage of 1-3 mg?kg -1 inhibited significantly the increase in the myocardial Gi? levels. Clonidine at the dosage of 0.3-3 mg?kg -1 partially reversed the decrease in the basal activity, and clonidine at the dosage of 1-3 mg?kg -1 showed the similar effect on the decrease in the Gpp (NH) p stimulated activity. Efaroxan, an I 1 imidazoline receptor antagonist, could partially reverse the inhibitory effect of clonidine on myocardial Gi? levels. Conclusion Clonidine can inhibit the elevation of myocardial Gi? levels, and the mechanisms of the inhibition may possibly be associated with the stimulatory effect of clonidine on I 1 imidazoline receptors.