Alteration Of Giα MRNA Expression And The Effects Of Clonidine And PNS On It After Severe Scald In Rats

Multiple organ dysfunction syndrome frequently occurs after severe scalds or burn injuries, among which, cardiac and pulmonary dysfunctions are most common critical reasons which may lead patients to death . It has been proved that the mechanisms of both cardiac and pulmonary dysfunctions were closely associated with the adenylate cyclase-cAMP signaling pathway. It was observed that the level of myocardial cAMP declined obviously in 30%TBSA scalded rats in our lab. The cAMP content was reduced to that of 31.6%, 36.9%, 35.6% and 30% of the control group at 6, 12, 24, 48 hour after scald in rats respectively(p<0.05); The cAMP content in lungs was also reduced obviously at 24 hour after smoke inhalation injury in rats, moreover, myocardial AC basic activity and Iso-,NaF-stimulated AC activity was inhibited significantly at 6, 12, 24, 48 hour after 30% TBSA or 24 hour after smoke inhalation injury in rats,while the activity of phosphodiesterase (PDE), which is responsible for cAMP degration, remained unchanged post burns ,indicating that the inhibition of cAMP content was not resulted from the increase of degradation but from deficiency of synthesis. Besides, FSK-stimulated AC activity remained unchanged post burns, suggesting that abnormal changes of the upstream of AC-cAMP signal transduction pathway are involved in the pathogenesis of cardiac and pulmonary dysfunction after severe scald in rats. Stimulatory G protein(Gs) and inhibitory G protein(Gi) are two key modulatory molecules of AC, Gs activates AC and then increases the synthesis of cAMP, while Gi shows an opposite effect to AC activity. It was found that in our previous study thedown-regulation of Gsα and the overexpression of Giα were responsible for the inhibition of AC,and the reduction of Gsα mRNA expression was one of the most important molecular mechanisms of the down-regulation of Gsα. However, there are still no reports about the molecular mechanisms of the overexpression of Giα.The alteration of Giα mRNA expression in myocardial and lung tissues and the effects of clonidine and PNS on it after 30% TBSA Ⅲ degree scald in rats were investigated with RT-PCR method. The results are as follows:1. The expression of Gi2α-mRNA and Gi3α-mRNA in myocardium and lung tissues elevated siginificantly after 30% TBSA Ⅲ degree scald. The expression of Gi2α-mRNA reached its peak value at 6h in myocardium and 3h in lung tissues, and Gi3α-mRNA reached its peak value at 3h in both tissues postburn.2. Clonidine and PNS significantly inhibited the expression of Gi2α- mRNA and Gi3α-mRNA after severe scald in rats.3. The expression of myocardial m2AchR-mRNA showed no significant alteration after 30% TBSA Ⅲ degree scald.Our results show that the increase of Giα protein in myocardial and lung tissue was most probably resulted from the enhancement of both Gi2α and Gi3α gene transcription. The inhibitory effects of Clonidine and PNS on the Gi2α and Gi3α gene transcription was one of the important mechanisms of the reduction of Giα expression, which subsequently lead to the alleviation of cardiac and pulmonary dysfunction after scald. In addition, the expression of m2AchR mRNA was unchanged postburn, suggesting that the changes of parasympathetic system was not closely related to the mechanisms of cardiac and pulmonary dysfunctions after severe scald in rats.