| Objective: Diabetic cardiomyopathy (DC) is a special chronic complication of diabetes mellitus (DM). It has a close relation with the high rate of heart failure and death in DM patients. A good many of studies showed that some major pathological hallmarks of DC were myocardial hypertrophy, myocardial necrosis, myocardium mesenchyme remodeling, myocardial fibrosis and so on. Extracellular matrix (ECM) is the principal part of myocardium mesenchyme, it is in the metabolic balance of continuous synthesis, secretion and degradation. Matrix metalloproteinases (MMPs) exist in myocardial tissue, they can degrade all the components of ECM and will make ECM lose its balance. The changes of MMPs protein expression levels and activities may play the key role during the occurrence and development of cardiomyopathy in DM. Panax notoginseng (Pn) and Astragalus membranaceus (Ast) are common Chinese herbs that could prevent and cure DM and its complications such as DC. In this study type 2 DM (T2DM) rat model was copied by giving Sprague-Dawlay (SD) rats high-fat diet and a low dose of streptozotocin (STZ). This model had some characteristics of insulin resistance, hyperglycemia and hyperlipidemia, which were similar to those of human T2DM. Then the protein expression level and activity of MMP-9 and the content of collagen (CL) in experimental animals myocardial tissue were detected in order to discuss the association between MMP-9 and cardiomyopathy in DM. Furthermore, Pn and Ast were given to experimental rats to explain the mechanism of these two Chinese herbs protective effects on myocardium. Methods: Ten of fifty SD rats were taken out randomly to be normal control rats (group A) and the rest were taken for test rats. The control rats were fed with general diet while the test rats were fed with high-fat diet (mixed 1% cholesterin, 0.35% cholic acid, 5% cooked lard and general diet together). Four weeks later, insulin resistance was induced in test group, then STZ 30mg/kg was injected into abdominal cavity to destroy pancreas. At the end of 6 weeks, the rats whose fasting blood glucose (FBG) was greater than 7.8mmol/L and insulin sensitivity decreased were considered as T2DM rats. Divided them randomly into 3 groups: T2DM model rats (group B), T2DM model rats treated with Pn (group C) and T2DM model rats treated with Pn and Ast (group D). The experiment lasted 18 weeks. At the end of 4 and 6 weeks, body weight, FBG, fasting insulin (FINS), insulin sensitivity index (ISI), serum triglyceride (TG) and total cholesterol (TC) levels in different group rats were measured. At the end of this experiment, FBG and TG, TC,high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), very low density lipoprotein cholesterol (VLDL-C) were detected. Observed myocardial microstructure and ultrastructure with light and electron microscopes. Measured myocardial CL content by picric acid -toluidine blue staining. Detected the protein expression level and activity of MMP-9 in myocardium by immunohistochemical staining and gelatin zymography. These graphic results were analyzed with computer image-analysis system and the integral optical density (IOD) counts of MMP-9 and CL were calculated. All the experimental data were dealt with SPSS11.0. Results: 1 Various indexes after 4 weeks: Been fed with high-fat diet for 4 weeks, test rats were heavier than normal control rats (P<0.05) and their FBG, FINS, TG, TC levels were all higher than those in control rats (all P<0.01). At the same time, ISI was lower in test rats (P<0.01). 2 Various indexes after 6 weeks: 2 weeks after STZ injection, the FINS level in test rats decreased to the level in control rats (P>0.05). Other features were retained. Body weight and FBG, TG, TC levels in test rats were all higher and ISI was lower than those in control rats (all P<0.01). Thus far, the T2DM rat model was accomplished. 3 Various biochemical indexes after 18 weeks: When the experiment was finished, FBG, TG, TC, LDL-C and VLDL-C in group B rats were all higher than those in group A rats. Andforegoing items in group C and D rats were lower than those in group B rats. HDL-C in group B rats was lower than that in group A, C and D rats. Compared with those in group C rats, HDL-C was higher and TC, LDL-C were lower in group D rats (all P<0.05). 4 Morphology: HE staining showed that cardiac tubes of group A rats were in order, cross striation was clear, karyon and ECM was normal. While in T2DM model rats, cardic muscle degeneration and ECM accumulation could be observed. Foregoing changes in group B rats were more severe than those in group C and D rats. Moreover, compared with group D rats, changes in group C rats were more serious. The myocardial ultrastructure of group A rats appeared that myofibril was in order, light and dark band was clear and the configuration of mitochondrion was normal. Group B rats had some pathological characteristics of myofibril disorder, mitochondrion edema, endoplasmic reticulum dilatation, CL hyperplasia, hepatin and lipofuscin deposition, capillary basement membrane incrassation etc. 5 Picric acid -toluidine blue staining: Cardiac tubes were green and CL fibres appeared blue after this special staining. The IOD of myocardial CL in group B rats (548.32±35.59) was 1.63 times greater than that in group A rats (335.57±21.25). And the IOD in group C (472.37±31.58) and D rats (422.64±26.75) respectively was 14% and 23% less than that in group B rats (all P<0.05).6 The protein expression level of MMP-9 in myocardium: The IOD of MMP-9 in group B rats (2104.69±117.25) was 1.80 times larger than that in group A rats (1172.40±99.22). And the IOD in group C (1742.65±105.21) and D rats (1650.00±126.24) respectively was 17% and 22% less than that in group B rats (all P<0.05). Related analysis showed that myocardial MMP-9 expression level had a positive correlation with FBG, LDL-C and CL content (r=0.752, 0.748 and 0.834, all P<0.01), a negative correlation with HDL-C (r=-0.706, P<0.01) in experimental rats. 7 The activity of MMP-9 in myocardium: The IOD of MMP-9 degraded band in group B rats (2450.41±183.49) was 2.24 times more than that in group A rats (1094.97±165.08). And the IOD in group C (2102.80±174.71) and D rats (1752.16±155.33) respectively was 14% and 28% less than that in group B rats (all P<0.05). Related analysis showed that the activity of MMP-9 in myocardial tissue had a positive correlation with FBG, LDL-C and CL content (r=0.725, 0.712 and 0.749, all P<0.01), a negative correlation with HDL-C (r=-0.733, P<0.01) in experimental rats. Conclusions: 1 The type 2 diabetic rat model that was induced by high-fat diet and a low dose of STZ had some characteristics similar to human T2DM. It would be available to study T2DM and its complications. 2 CL hyperplasia and ECM remodeling were principal... |
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