Systolic Heart Function Evaluated By Strain And Strain Rate Analysis In Metabolic Syndrome Rat And Related Study

Part One Establishment of Metabolic Syndrome Model With Sprague Dawley RatBackgroundsAnd Objectives:Metabolic Syndrome(MS) is a cluster characterized by insulin resistance(IR) including decreased glucose tolerance, hypertriglyceridemia, low high-density lipoprotein level, hypertension and obesity. MS is related to the development of cardiovascular disease closely. However, it's pathogenesis is unclear. Genetic factors, environment, unhealthy life style are all involved in the development of MS. Therefore, it's necessary to establish animal model of MS so as to make related studies and explore the complex pathophysilogical mechanism.Animal models of MS include genetic model, transgenetic or gene knock-out model, environment-induced model and drug-induce model, and so on. However, there're some deficiencies in the present models. It's necessary to employ a different method to induce an appropriate model. Therefore, Sprague Dawley(SD) rats are used to establish animal model of MS by life style intervention combined with low-dose drug intervention. MethodSixteen male SD rats aged at six week were divided into the MS model group and the control group. Each group included eight rats. After one-week adaptive feeding, the rats divided in the MS model group were injected with streptozocin(STZ, 15mg/kg) through the tail vein after over night fasting. After injection, these rats continued to be fasted for eight hours and then were fed with high-fat diet and with water containing 0.02% Nitro-L-arginine methyl ester (L-name) and 10% glucose. The rats of the control group were fed with standard diet and with distilled water. All these rats were fed up to six weeks. Body weight, blood pressure, fasting glucose(FPG), fasting insulin(FINS), triglyceride(TG), total cholersterole(TC), high-density lipoprotein(HDL), low-density lipoprotein(LDL) and oral glucose tolerance test (OGTT) were examined periodically at the beginning and at the end of the study respectively. FPG, TG TC, HDL and LDL levels were examined by automatic biochemical analyzer. FINS level was examined by ELISA method. The rats of the MS model group were given 20% glucose solution by intragastric administration. Then blood glucose levels at 0,15,30,45,60,90 and 120 minutes were tested by blood glucose meter. The area under the curve of OGTT was calculated. SPSS 17.0 software package was used to make statistical analysis. Measurement data was described as mean±SD(x±s). Repeat measure varience analysis was used to compare the before and after control datas. It meant the difference was significant statistically if P value was less than 0.05.Results1. Body weight. There were significant difference in alterations of body weight between MS model group and the control group, body weight of MS model rats was significantly higher than that of the controls (F=11.406, P=0.005) after being fed for six weeks. 2. Fasting glucose, insulin levels and HOMA-IR. There were no significant differences in alterations of FPG level between MS model group and the control group (F=0.035, P=0.855) after being fed for six weeks. There were significant differences in alterations of FINS level between MS model group and the control group, FINS level in MS model rats was significantly higher than that of the controls (F=12.232, P=0.004) after being fed for six weeks. There were significant differences in alterations of HOMA-IR level between MS model group and the control group, HOMA-IR level in MS model rats was significantly higher than that of the controls (F=11.966, P=0.004) after being fed for six weeks.3. Oral glucose tolerance test. There were significant differences in alterations of AUC of OGTT between MS model group and the control group, AUC of OGTT in MS model rats was significantly higher than that of the controls (F=8.717, P=0.010) after being fed for six weeks.4. Plasma lipid levels. There were significant differences in alterations of TG level between MS model group and the control group, TG level in MS model rats was significantly higher than that of the controls (F=5.525, P=0.034) after being fed for six weeks. There were significant differences in alterations of TC level between MS model group and the control group, TC level in MS model rats was significantly higher than that of the controls (F=17.096, P=0.001).There were no significant differences in alterations of HDL level between MS model group and the control group (F=0.057, P=0.815)5. Blood pressure. There were significant differences in alterations of SBP level between MS model group and the control group, SBP level in MS model rats was significantly higher than that of the controls (F=17.678, P=0.001). There were significant differences in alterations of DBP level between MS model group and the control group,DBP level in MS model rats was significantly higher than that of the controls (F=10.755, P=0.005)Conclusions1. Metabolic disorder blood glucose could be induced by low-dose STZ combined with high-fat and high-glucose feeding.2. Metabolic disorder of blood lipid could be induced by high-fat and high-glucose feeding.3. Weight gain and obesity could be induced by high-fat and high-glucose feeding.4. Hypertension could be induced by low-dose L-name.5. MS model rat could be established by the method in our experiment.Part Two Systolic Left Ventricular Function Evaluated By Strain and Strain Rate and Related StudyBackgroundsAnd objectives:Studies of cardiac function in MS were focused on diastolic cardiac function, especially on the early alterations of diastolic heart function. With respect to the early systolic heart function, no alterations had been found in MS because probably no sensitive techniques could be used. Therefore, it's greatly meaningful to adopt a sensitive method to examine the early alterations of systolic heart function in MS. The most present two-dimensional echocardiography and speckle tracking based strain and strain rate analysis evaluate left ventricular function independent on the ventricular volume and are sensitive compared with the traditional echocardiography techniques. However, few researches on left ventricular function in MS employing this technique has been reported. It's necessary to carry out studies to explore diagnostic significance of this technique in heart function examination in MS.Epicardial adipose tissue(EAT) is also an active endocrine organ and probably associated closely with the development of cardiovascular disease. However, no adequate studied have been made about it and our understanding about it is limited. So it's necessary to carry out studies on the relationship between EAT and cardic function in MS to explore the possible mechanism that EAT involves in the pathogenesis of cardiovascular disease.With respect to the lack of researches on evaluation of the systolic left ventricular function in MS employing the two-dimensional echocardiography and speckle tracking based strain and strain rate analysis and our limited understanding about the relationship between EAT and cardiovascular disease, we made this experiment to evaluate the alterations of left ventricular systolic function employing this most present echocardiography technique and to explore the correlation between EAT and left ventricular function in MS rats.Methods1. Randomization, feeding, and examinations of characters of MS. See Part One.2. Echocardiography examination. Parasternal short axis images at papillary muscle level were acquired with the use Vevo(?) 2100 color Doppler small animal ultrasonic imaging system and with 16MHz derector. Three two-dimensional images of whole cardic cycle with clear left ventricular endocadium and epicardium borders were recorded and left ventricular anterior wall and posterior wall images at papillary muscle level were obtained with M-mode echocardiography. All these images were stored and analyzed off-line. Left ventricular end diastolic internal diameter(LVIDd), end systolic internal diameter(LVIDs), anterior wall thickness(LVAW) and posterior wall thickness(LVPW) were evaluated with M-mode image and then end diastolic volume, end systolic volume and fraction of shortening were calculated. Left ventricular ejection fraction (LVEF,%) was calculated by Teichholtz equation. According to the sixteen-segment dividing principle recommended by American Society Of Echocardiogphy, the parasternal left ventricular image at papillary muscle level was divided into six segments including anterior free wall, lateral wall, posterior wall, inferior free wall, posterior septal wall and anterior septum. At least fourteen frames of high-frame two-dimensional image(frame frequency=100frames/s) of each cardiac cycle were analyzed with speckle tracking method. A clear parasternal left ventricular image at papillary level was selected and frozen at the end of systole. Endocardium was bordered manually and the soft system covered the entire myocardium automatically and tracked the myocardial motions. Endocardial and epicardial systolic circumferential strain and strain rate of each segments were analyzed automatically. The curves of strains or strain rates of successfully-tracked segments and the peak strains or strain rates on these curves were also calculated automatically. The strains and strain rates of six segments were averaged as to evaluate the left ventricular deformational ability or systolic function.3. Isolation of heart, left ventricle and epicardial adipose tissue. After all examinations were accomplished at week six, all the rats were fasted and anesthetized. Thoracic cavity was opened and heart was exposed. Then heart and EAT were isolated and weighted separately. Left ventricle was isolated further and weighted. Myocardial tissue was harvested, fixed with 4% formaldehyde and then was prepaired into paraffin embedded sections. These paraffin embedded sections were stained for morphology evaluation or analyzed by immunohistochmestry. EAT was examinged by genome-wide expression profiling microarray.4. Statistical analysis. SPSS17.0 software package was used to make statistical analysis. Measurement data was described as mean±SD(x±s). T-test was used to compare the data between two independent groups as variance was equal, otherwise t'-test would be used. Repeat measure varience analysis was used to analyze before and after control datas. Correlation between two variables was analyzed with linear correlation analysis by Pearson method and then partial correlation analysis would be made further. It meant the difference was significant statistically if P value was less than 0.05.Results1. Characters of metabolic syndrome in two groups. See part one.2. Left ventricle structure and systolic function evaluated with M-mode echocardiography. There were significant differences in alterations of LVAWd and LVAWs between MS model group and the control group, LVAWd and LVAWs in MS model rats were significantly thicker than that of the controls (F=5.427, P=0.035; F=5.467, P=0.035) after being fed for six weeks. There were significant differences in alterations of LVIDd between MS model group and the control group, LVIDd in MS model rats was significantly shorter than that of the controls (F=14.416, P=0.002). There were significant differences in alterations of LVPWd and LVPWs between MS model group and the control group, LVPWd and LVPWs in MS model rats were significantly thicker than that of the controls (F=8.999, P=0.010; F=14.613, P=0.002). There were no significant differences in alterations of LVEF between MS model group and the control group (F=0.265, P=0.615)3. Left ventricular endocardial systolic circumferential strain and strain rate. There were no significant differences in alterations of left ventricular systolic endocardial circumferential strian(EndoCircumS) and strian rate (EndoCircumSR) between MS model group and the control group (F=0.574, P=0.461; F=0.370, P=0.553) after being fed fot six weeks.4. Left ventricular epicardial systolic circumferential strain and strain rate. There were significant differences in alterations of left ventricular systolic epicardial circumferential strian (EpiCircumS)and strian rate((EpiCircumSR)between MS model group and the control group (F=8.797, P=0.010; F=6.917, P=0.020) after being fed fot six weeks.5. Comparisons of deformational ability between endocardium and epicardium within each group. Left ventricular systolic EndoCircumS of two groups were significantly higher than EpiCircumS from the beginning to the end of our study (t=-18.421, P=0.000; t=-6.883, P=0.000; t=-9.0431, P=0.000; t=-7.791, P=0.000),and EndoCircunSR were also significantly higher than EpiCircumSR (t=-13.028, P=0.000; t=-5.827, P-0.000; t=-8.182, P=0.000; t=-7.675, P=0.000).6. Heart, left ventricle and epicardial adipose tissue mass. There're no differences in heart, left ventricle and epicardial adipose tissue masses between two grous (t=0.266, P=0.794; t=1.878, P=0.081), EAT mass of the MS group was significantly heavier than the control group (t=2.803, P=0.014)7. Correlations between epicardial adipose mass and systolic circumferential strain or strain rate of left ventricle. EAT mass was correlated to EpiCircumS and EpiCircumSR significantly (r=0.679, P=0.004; r=0.712, P=0.002) and not associate with EndoCircumS or EndoCircumSR (r=0.223, P=0.406; r=0.209, P=0.438). Partial correlation analysis showed that EAT mass was not correlated to EpiCircumS and EpiCircumSR (r=0.014, P=0.979; r=0.369, P=0.471) after being adjusted by body weight, FPG, TG, TC, HDL, LDL, OGTT, SBP and DBP.8. Left ventricular morphology and immunohistochmestry. No differences in morphology of epicardium and encardium in MS model rats were found as compaired with that in the controls when the study was ended. Morphology of epicardium was also not different from that of endocardium in MS model rats, weren't differences in expressions of collagen-Ⅰand collagen-Ⅲbetween epicardium and endocardium in MS model rats. Expressions of collagen-Ⅰand collagen-Ⅲof epicardium and endocardium in MS model rats weren't different as compaired with that of the controls.9. Differential expression genes. Geneome-wide expression profiling microassay showed that there're differential expression genes in heart hypertrophy, myocardial contrctile and adipocytokines pathways and lipid storage.Conclusions1. MS rats exhibited left ventricular hypertrophy and remodeling.2. MS rats showed early regional left ventricular systolic dysfunction.3. EAT was closely related to left ventricular epicardial systolic dysfunction in MS rat.4. Two-dimensional and speckle tracking based strain and strain rate analysis could identify the early regional left ventricular systolic disfunction in MS rat.5. The differential expression genes were probably important regulatory factors for epicardium systolic function in MS.