The Effects Of Antagonist To Ⅰ-type Receptor For Angiotensin Ⅱ On Cardiomyocytic Apoptosis In Rats With Heart Failure

Objective: To explore the effects of Losartan on cardiomyocytic apoptosis in rats with heart failure, which is a new medicine as an antagonist toⅠ-type receptor for angiotensinⅡ(AT1R), so as to protect cardiomyocytes from apoptosis induced by it. To aim at that, the expressive changes of pro-apoptotic protein Bax and anti-apoptotic protein Bcl-2 are analyzed, the activities of serum enzymes associated to heart failure are determined and the myocardial ultra-micro structures are observed. Because studies have confirmed recently that cardiomyocytic apoptosis, leading to decrease in the number of myocardial cells,could occur within a process of heart failure. It could play an important role in pathological mechanism of heart failure. The receptors for angiotensinⅡcould be activated and induce cardiomyocytic apoptosis when heart failure outbreaks. Losartan, an antagonist of AT1R, could be applied to treatment of heart failure, prevention of ventricular remodeling and improvement of cardiac function, but its mechanism related to inhibition of apoptosis, improvement of myocardial ultra-micro structure and reduce of enzyme leakage in heart failure is unclear until now. Methods: Twenty-four SD rats (male, 8 weeks age) were divided randomly into the control group, heart failure group and treatment group with each group of eight. Adriamycin (ADR) was injected into the abdominal cavity of rats from the heart failure group and treatment group, with 4 mg/kg, once a week and total of six weeks. At the same time, the rats in the treatment group were given Losartan with 20 mg/kg·d by oral administration. The rats in the control group were injected into the abdominal cavity with the same volume of 0.9% NaCl solution. After the last administration, the activities of serum CPK, CK-MB and LDH were detected, the ultra-micro structural changes of rat cardiomyocytes were observed by electron microscopy, the myocardial cell apoptosis was detected by deoxyribonuclease terminal labeling in situ method (TUNEL), and the Bax and Bcl-2 protein expressive levels in rat cardiomyocytes were detected by immunohistochemistry. Results:①Compared with that in the control group, the organizational structure of rat myocardial cells in the heart failure group was injury significantly. When myocardial ultra-micro structure was observed, there was an obvious cardiac myocyte necrosis in the heart failure group. At the same time, the muscle fiber fracture, partial dissolved myofibril, damaged sarcolemma and mitochondrial membrane, partial destruction of nuclear membrane and apoptotic cells could be observed also in myocardial cells of the heart failure group. The detections of activities of serum CPK, CK-MB and LDH were showed that the activities of CPK in the control group and heart failure group were 132±59 U / L and 1541±408 U / L respectively,the activities of CK-MB in both groups were 12±6 U / L and 1135±347 U / L respectively, and the activities of LDH in both groups were 186±75 U/ml and 2856±581 U/ml respectively. The activities of serum CPK, CK-MB and LDH in the heart failure group were significantly higher than those in the control group (P <0.01). The results of cardiomyocyte apoptosis index in the control group and the heart failure group were 4.02±0.18 and 25.70±4.13 respectively. The cardiomyocyte apoptosis index was significantly increased in heart failure group (P<0.01). The expression levels of Bax protein in control group and heart failure group were 31.22±1.21 and 46.96±2.57 respectively. The expression levels of Bcl-2 protein in both groups were 39.67±2.83 and 28.35 respectively. The expression level of Bax protein in the heart failure group was higher than that in the control group and the expression level of Bcl-2 protein in the heart failure group was lower than that in the control group (P <0.01).②Compared with that in the heart failure, the ultra-micro structure damage of myocardial tissue in the treatment group was reduced. The majority of muscle fiber was integrity. The nuclear morphology and structure were normal. The activities of serum CPK in the treatment group and the heart failure group were 599±125 U/L and 1541±408 U/L respectively. The activities of serum CK-MB in both groups were 176±56U/L and 1135±347 U/L. The activities of serum LDH in both groups were 622±161 U/ml and 2856±581 U/ml respectively. The leakage of enzymes in the treatment group was significantly reduced than that in the heart failure group (P <0.01). The detection of cellular apoptosis was showed that AI in the treatment group and the heart failure group were 12.00±1.34 and 25.70±4.13 respectively, The cardiomyocyte apoptosis index was significantly decreased in the treatment group compared with that in the heart failure group (P <0.01). The expression of Bax protein in the treatment group and heart failure group were 33.51±1.43 and 46.96±2.57 respectively. The expression of Bcl-2 protein in the treatment group and heart failure group were 28.35±1.55 and 36.34±2.60 respectively. The expression of Bax protein was significantly reduced and the expression of Bc1-2 protein was increased in treatment group compared to the heart failure group (P <0.01).③Compared with that in the control group, the damage of myocardial ultra-micro structure in the treatment group was not obvious. The activities of serum CPK in the treatment group and the control group were 599±125 U/L and 132±59 U/L. The activities of serum CK-MB in both groups were 176±56U/L and 12±6U/L respectively. The activities of serum LDH in both groups were 622±161U/ml and 186±75U/ml respectively. The activities of serum CPK, CK-MB and LDH in the treatment group were higher than those in the control group (P <0.05). The cardiomyocyte apoptosis index in the treatment group and the control groups were 12.00±1.34 and 4.02±0.18 respectively. The cardiomyocyte apoptosis index in the treatment group slightly was increased (P <0.05). The expressions of Bax protein in the treatment group and the control group were 33.51±1.43 and 31.22±1.21 respectively. The expressions of Bcl-2 protein in both groups were 36.34±2.60 and 39.67±2.83 respectively. Compared with those in the control group, the differentiation of Bax and Bcl-2 protein expression was no obvious (P> 0.05). Conclusion: A rat model with heart failure could be achieved by injecting repeatedly Adriamycin into rats'abdominal cavity, which is a simple and reliable method. The myocardial ultra-micro structure is significantly impaired when heart failure happens. For the leakage of them, the activities of serum enzymes are significantly increased. Cardiomyocyte apoptosis occurs in the course of heart failure. The expression of Bax protein is increased and the expression of Bcl-2 protein is reduced. Losartan can significantly increase the expression of Bcl-2 protein and decrease the expression of Bax protein, so as to achieve effective inhibition of cardiomyocyte apoptosis. Both of the damage of myocardial ultra-micro structure and the leakage of enzymes are reduced. So Losartan plays a positive role in decreasing the damage of cardiomyocytes and makes the process of heart failure slowing down.