The Expression Of Angiotensin ? In Myocardial Tissue Of Rats With Arrhythmias And The Influence On Brain Natriuretic Peptide

Objective:Due to the abrupt occurrence and absence of characteristic pathological changes in autopsy and microscopic examinations,identification of the ventricular arrhythmia,which is the major part of sudden cardiac death?SCD?,becomes a major difficulty in forensic medicine appraisal work.Brain natriuretic peptide?BNP?is a major marker for evaluating cardiac function and has been widely used in clinical practice.Recent researches show that BNP is also useful for identification of sudden cardiac death in forensic pathology.Previous studies showed that the concentration of BNP and BNPmRNA in plasma and ventricular myocytes significantly increased at about 30 minutes after arrhythmia.However,the duration of SCD due to arrhythmia was short,and the level of BNP may not be detected within short time.In vitro,Angiotensin ??Ang??can result in the synthesis and secretion of BNP in cardiac myocyte,and it is closely related to the occurrence of myocardial infarction?MI?and arrhythmia.In present study,we investigated the expression of BNP and Ang? protein as well as mRNA in left ventricular myocardial tissues of rats with ventricular arrhythmias,and studied the impacts on BNP.Losartan potassium?Ang? antagonist?was used to explore the possible mechanisms of BNP expression induced by arrhythmia,in order to explore the earlier biochemical indexes in diagnosis of SCD in forensic practice.Methods:Rats were anesthetized by intraperitoneal injection with 2%sodium pentobarbital?1.5mg/100g?and were fixed in the supine.10%BaCl₂ solution was injected through intravenous by a micro-injector pump in a dose of 0.004ml/100g to establish the arrhythmia models.Cardiac arrhythmia induced by BaCl₂ was continually monitored by 2-lead electrocardiogram?ECG?via Powerlab biological signal processing system.Rats were randomly divided into BaCl₂ group?n=12?and Saline groups?n=12?,each group was divided into 2 subgroups?30min subgroup and 60min subgroup,each subgroup contained 6 rats?.BaCl₂ group animals were injeceted BaCl₂and killed by double dose of BaCl₂ at the corresponding time?30 min and 60 min?,while the Saline group animals were injected with the same volume of saline and killed by dislocation of cervical vertebra.6 rats were killed by dislocation of cervical vertebra after 30 minutes of BaCl₂-induce arrhythmia.The BNP and Ang? protein and mRNA in myocardium of rats were detected by immunohistochemistry?IHC?,Western blot and Real-time PCR.Then,SD male rats?n=24?were divided into 2 groups?each n=12?as Vehicle and LP,randomly.Rats in each group were intraperitoneally injected the solvents or inhibitors solution 30 minutes before arrhythmia and killed at the corresponding time.BNP and Ang? were detected according to the previous time and methods.Result:1.Cardiac arrhythmias induced by BaCl₂ happened within several seconds and the mainly types of arrhythmias were ventricular tachycardia and ventricular fibrillation.2.Some nonspecific changes such as edema,hemorrhage,myocardial wave,and enhanced eosinophilic staining were present in the myocardium in sections stained with H-E.3.The expression of BNP and Ang? in myocardium of rats increased after 30minutes of BaCl₂-induce arrhythmia,but Ang? decreased after 60 minutes of BaCl₂-induce arrhythmia.4.Vehicle groups were similar to the BaCl₂ group.Compared with Vehicle group,the levels of BNP in left ventricular were decreased in LP groups after 30 minutes of BaCl₂-induce arrhythmia.BNP mRNA were increased after 60minutes of arrhythmia.Conclusion:1.Arrhythmias can lead to myocardial ischemia.2.Arrhythmias can induce the expression of Ang?.2.Ang? antagonist suppress the synthesis of BNP in myocardial tissue of rats with arrhythmia.