Effect On Myocardial Fibrosis In Diabetic Rats After The Blockage Of The Local Rennin-angiotensin-aldosterone System At Different Sites

Objective To study the effect of the local renin-angiotensin-aldosterone system on myocardial fibrosis in diabetic rats.To view the effect of benazepril alone or in combination of spironolactone on myocardial fibrosis in diabetic rats.Methods 32 male Wistar rats were randomly divided into four groups, namely normal control group(NC group), diabetes mellitus group(DM group), benazepril intervention group(BEN group) and benazepril combined with spironolactone intervention group(SPI group).There are eight rats in each group. NC group was fed with the normal diet. The remaining rats were used to establish diabetic animal models by feeding high glucose and lipid diet and injecting low-dose streptozotocin. After the success of modeling, BEN group and SPI group were respectively intervened by intragastric administration with benazepril (1mg/kg) and benazepril (1mg/kg) plus spironolactone (2mg/kg), NC group and DM group were given normal saline once a day for 8 weeks. All rats were anesthetized by 10% chloral hydrate before we took the myocardial samples. Radioimmunoassary and masson staining were repectively used to detect the levels of myocardial angiotensinⅡ, aldosterone and the volume fraction of myocardial collagen. The expression of myocardial TGF-β1, Smad3 and Smad7 protein was determined by immunohistochemistry. myocardial ultrastructure was observed by the electron microscopy.Results1. The levels of myocardial angiotensinⅡ, aldosterone: The levels of myocardial angiotensinⅡin DM group is higher than NC group, BEN group and SPI group, the difference was statistically significant. The levels of aldosterone in DM group is higher than NC group, BEN group and SPI group, the differences were statistically significant; SPI group is higher than NC group and BEN group, the difference was statistically significant.2. Myocardial ultrastructure and masson staining results:Myocardial fibrosis in DM group significantly increase, collagen volume fraction is higher than NC group, BEN group and SPI group. Compared with DM group, myocardial fibrosis in BEN group, SPI group are attenuated.3. The expression of myocardial TGF-β1, Smad3, Smad7 protein:The myocardial TGF-β1 and Smad3 in BEN and SPI group are higher than NC group, but less than DM group. The myocardial Smad7 in BEN and SPI group are less than NC group, but higher than DM group.4. Comparison of serum potassium:The serum potassium in SPI group is higher than DM group, BEN group and NC group. In DM group, BEN group and NC group there was no significant difference.Conclusion1. The level of local RAAS in diabetic rats involves in the formation of myocardial fibrosis, one of the mechanisms may be related to TGF-β/Smad signal transduction pathway.2. Using benazepril (angiotensin converting enzyme inhibitor), spironolactone (aldosterone antagonist) blocking the RAAS different sites, myocardial fibrosis in diabetic rats could be reduced.