The effect of Shenmai injection on cardiac myocyte apoptosis after hypoxia

AIM: To observe the effect of Shenmai injection, a chinese medicine, on apoptosis of cardiac myocytes after hypoxia. METHODS: Cardiac myocytes were separated from neonate rat heart and cultivated in vitro. Hypoxia condition was induced by mixture of 95%N2 and 5%CO2. Cells were exposed to hypoxia for 6 h or 12 h and treated with Shenmai injection (5 mL/L) from 24 h before hypoxia until the end of hypoxia. First, apoptosis was detected with Annexin V-FITC and PI staining by flowcytometry. Then, the activity of cardiac myocyte mitochondria was observed by MTT method. Mitochondria membrane potential and the activity of caspase 3,7 were also measured by laser scan microscopy and multi-detection microplate reader, respectively. RESULTS: The apoptotic cells became more and more with prolonged hypoxia. Shenmai injection enhanced mitochondria activity, kept membrane potential, inhibited the activation of caspase3,7 and then decreased apoptotic cells (P<0.01). CONCLUSION: Hypoxia induces apoptosis in cardiac myocytes by mitochondria pathway. Shenmai injection can decrease cardiomyocyte apoptosis after hypoxia, the mechanism is related to mitochondria membrane potential stabilization and caspase inhibition.     

Energy metabolism and apoptotic effect of microwave radiation on rat myocardial cells

AIM: To investigate the effect of microwave radiation at different intensities on the rat myocardium and its possible mechanism.METHODS: The rats were radiated by the intensity of 500, 1 000, 1 500 and 2 000 W/m² with 2 450 MHz microwave for 6 min. The heart tissue was collected 6 h after microwave radiation. ATP and mitochondria complex Ⅳ and Ⅴ were measured. The changes of the tissue structures were observed under transmission electron microscope. The apoptosis of the myocardial cells was detected by a cell analyzer. The protein level of cleaved caspase-3 was determined by Western blotting.RESULTS: The concentration of ATP and activity of mitochondria complex Ⅳand Ⅴ signi-ficantly decreased compared with control group in the cardiac tissues. The decreased number, morphological abnormalities such as dissolved cavitation, matrix and obvious tumefaction of mitochondria were observed under transmission electron microscope. The microwave radiation induced the apoptosis of myocardial cells in the rats. The cell apoptotic rate and the protein level of cleaved caspase-3 increased with increasing intensity of microwave radiation(P<0.05).CONCLUSION: Microwave radiation has obvious injury effect on the rat heart, which can cause cardiac energy metabolism dysregulation and cardiac myocyte apoptosis.     

Mechanisms of heart failure induced by adriamycin

AIM: To investigate the changes of cardiac function, oxidative stress and apoptosis in myocardium of rat model of heart failure induced by adriamycin (ADR). METHODS: At the end of the study, we observed content of malondialdehyde (MDA), activity of superoxide dismutase (SOD) and apoptosis. Expression of P53 protein and p53 mRNA were measured with immunohistochemical method and RT-PCR, respectively. RESULTS: Our data showed that content of MDA increased, activity of SOD decreased and apoptosis in myocardium happened while cardiac function decreased after ADR treatment. p53 gene expression and P53 protein obviously increased in heart failure group. CONCLUSION: There were oxidative stress and apoptosis occurred significantly in a model of heart failureinduced by ADR. p53 gene might play an important role in the apoptosis. Correlation analyses suggested that apoptosis in myocardium was related to oxidative stress in ADR-induced heart failure model.     

Relationship between 3-nitrotyrosine and myocardial cell apoptosis in rat diabetic cardiomyopathy

AIM: To explore the relationship between 3-nitrotyrosine (3-NT) level in hearts or blood and myocardial cell apoptosis in rat diabetic cardiomyopathy (DCM). METHODS: Sixty Sprague-Dawley (SD) rats (male, 8-week-old) were randomly divided into 4 groups: normal group, diabetic cardiomyopathy group (DCM group), diabetic rats treated with valsartan (40 mg·kg^-1·d^-1, D+V group) and DCM rats treated with valsartan (40 mg·kg^-1·d^-1, DCM+V group). Apoptotic index (AI) of rat cardiac myocytes was examined by TUNEL. The expression index (EI) of 3-NT in rat cardiac myocytes was examined by immunohistochemistry. The 3-NT concentration in rat serum was examined by ELISA. RESULTS: (1) Significant differences of the heart weight indexes among the 4 groups were observed (P<0.01). The heart weight indexes in DCM group and DCM+V group were higher than those in normal group and D+V group (P<0.01). (2) The EI of 3-NT in the cardiac myocytes was positively correlated with the AI of the cardiac myocytes in the same group (P<0.01), but the concentration of 3-NT in blood had no correlation with the AI of cardiac myocytes (P>0.05). (3) The difference of AI of cardiac myocytes among the 4 groups had statistical significance (P<0.01). The arrangement from high to low of AI was DCM group > D+V group and DCM+V group > N group (P<0.05). (4) The EI of 3-NT in DCM group was the highest as compared to other groups (P<0.05). (5) No statistical difference of 3-NT concentration in blood among the 4 groups was observed (P>0.05). CONCLUSION: (1) The expression of 3-NT in DCM myocardial tissues in SD rats is significantly increased and closely correlated with the apoptosis in myocardial cells. Valsartan inhibits 3-NT expression in DCM myocardial cells, thus inhibits the DCM myocardium apoptosis. (2) The 3-NT level in blood can not be true for reflection of 3-NT expression in DCM myocardial tissues and its effect on myocardial cell apoptosis.     

Effects of nitric oxide on mitochondrial function in cardiomyocytes: pathophysiological relevance

It is now clear that both endogenous and exogenous sources of nitric oxide (NO) exert important modulatory effects on cardiac mitochondrial function. There is also growing evidence that NO can be produced within the mitochondria themselves. NO can influence respiratory activity, both through direct effects on the respiratory chain or indirectly via modulation of mitochondrial calcium accumulation. At pathological concentrations, NO causes irreversible alterations in respiratory function and also interacts with reactive oxygen species (ROS) to form reactive nitrogen species (RNS), which may further impair mitochondrial respiration and even lead to open the mitochondrial permeability transition pore and induce cell death. Diabetes, aging, myocardial ischemia, and heart failure are all associated with altered ROS generation, which can alter the delicate regulatory balance of effects of NO in the mitochondria.     

Hypoxia facilitates rapid pacing-induced calcium transient alternations in ventricular myocytes

AIM:To explore the effect of hypoxia on rapid pacing-induced calcium transient alternations in ventricular myocytes.METHODS:Ventricular myocytes were isolated from the heart of adult SD rats and cultured in serum-free hypoxic fluid to set up an in vitro model of hypoxia-induced cardiac injury. The calcium transient and its alternations were investigated under confocal laser scanning microscope. The mitochondrial function was also examined by WST-8 kit. RESULTS:Under normoxic condition, the ventricular myocytes were claviform. Low frequency of pacing, ranging from 60 to 240 min^-1, induced calcium transient, but not calcium transient alternations, which was elicited by the pacing over a threshold frequency of(288 ±27)min^-1. Exposure of the ventricular myocytes to hypoxia did not obviously affect the morphology of the cells, but reduced the threshold frequency of pacing to(227±26) min^-1(P<0.05). Additionally, exposure of the cells to hypoxia repressed the activity of mitochondrial dehydrogenase from(100.2±8.7)%(control group) to(57.6±7.5)%, which was partially blocked by L-type Ca²⁺ channel inhibitor. CONCLUSION:Hypoxia facilitates calcium transient alternations induced by rapid pacing, and the calcium transient alternations are involved in the hypoxia-injured mitochondria function.     

Effect of endoplasmic reticulum stress on cardiac myocyte apoptosis in mouse congestive heart failure induced by myocardial infraction

AIM: To explore the effect of endoplasmic reticulum stress on cardiac myocyte apoptosis in mouse congestive heart failure induced by myocardial infraction.METHODS: The mouse model of heart failure was established by ligating the left anterior descending coronary to produce acute myocardial infarction. Thirty-two mice were divided into 4 groups: sham group and groups of post-operation at time points of 2, 4 or 6 weeks, respectively. The ventricular dilatation and left ventricular functions were assessed by echocardiography. The expression of GRP78, CHOP, caspase-12, cleaved caspase-12, JNK and phosphorylated-JNK was detected by Western blotting. The cardiac myocyte apoptosis was determined by terminal deoxynucleotidyl transferase mediated dUTP-biotin nick end labeling (TUNEL).RESULTS: The cardiac expression of endoplasmic reticulum chaperones GRP78 was significantly increased in the hearts with functional failure. The upregulated expression of CHOP, phosphorylated-JNK and cleaved caspase-12 illuminated that the CHOP-JNK- caspase-12 dependent pathways for endoplasmic reticulum-initiated apoptosis were activated in the heart with functional failure by myocardial infraction. CONCLUSION: These findings suggest that the congestive heart failure induced by myocardial infraction is associated with endoplasmic reticulum stress and activation of CHOP, JNK, caspase-12 dependent pathways for endoplasmic reticulum-initiated apoptosis.     

PERK signal pathway is involved in hypoxia-induced endoplasmic reti-culum stress and apoptosis in cultured cardiac myocytes

AIM:To investigate the role of endoplasmic reticulum(ER) stress in the process of hypoxia-induced neonatal rat myocardial injury through PERK signal pathway. METHODS:Neonatal rat cardiac myocytes were randomly divided into control group and hypoxia 1 h, 4 h, 8 h, 12 h and 24 h groups. Cell viability was evaluated by determining the intracellular content of ATP. Apoptosis was measured by high-content analysis(HCA) cell imaging system. The protein levels of GRP78, calreticulin, p-PERK, p-eIF2α, ATF4 and CHOP were detected by Western blotting at different time points. The primary cultured neonatal rat cardiac myocytes were treated with an agonist of PERK pathway salubrinal and the cell apoptosis was observed under hypoxia. RESULTS:In the early phase, hypoxia induced an increase in the expression of calreticulin and GPR78. In the middle phase of hypoxia, the levels of p-PERK, p-eIF2α and ATF4 were increased. In the later phase of hypoxia, increased CHOP level was also observed. Salubrinal effectively protected the cardiac myocytes from hypoxic injury. CONCLUSION:Hypoxia activates ER stress in cardiac myocytes and also activates PERK signal pathway. PERK signaling protects cardiac myocytes from hypoxic damage in the early stage and triggers apoptosis of the cells in the later phase.     

Catastatic pathways of adenosine monophosphate in failing cardiac myocytes of patients with congenital heart disease()

AIM:To study the metabolic pathways of adenosine monophosphate (AMP) in the chronic failing cardiac myocytes of patients with congenital heart disease (CHD). METHODS:RESULTS:There was no significant statistic difference among the contents of AMP in three groups (P≥0. 05). The concentration of Ado was lower in the group C (P≤0. 05) and the concentration of IMP was higher significantly (P≤0. 05). There was a significant increase in the ratio of IMP/Ado in the three groups. Negative relationship was found between pre-operative EF of left ventricle and IMP/Ado (K constant). The higher K constant was, the higher incidence of post-operative heart failure would be. CONCLUSION: The metabolic pathway of AMP in the failing cardiac myocytes of CHD may go along with the way to create more IMP. The lower of pre-operative ejection fraction of left ventricle indicates the abnormal change of AMP catabolism, post-operation heart failure may be an important complication in these patients.     

Study on apoptotic and nonapoptotic injuries induced by hydrogen peroxide in cardiac myocytes

AIM: To study apoptotic injury induced by reactive oxygen species-hydrogen peroxide (H₂O₂) on cardiac myocytes.METHODS:Cultured rat neonatal cardiac myocytes were treated with H₂O₂ of various concentration to observe apoptotic injury of cardiomyocytes by agarose gel electrophoresis, Giemsa-stained smears of cell, and flow cytometry, meanwhile lactate dehydrogenas (LDH) and malondialdehyde(MDA) were determined to assess the effect of H₂O₂ on lipid peroxidation and permeability of the plasma membrane. RESULTS: 5 mmol/L H₂O₂ caused cultured cardiomyocytes apoptotic morphological characteristics, including nucleosomal DNA fragmentation in myocytes by agarose gel electrophoresis (DNA ladder), cell shrinkage, nuclear condensation, and chromatin margin by Giemsa-stained cell smears, and aneuploid peak(AP)-apoptotic bodies occurrence by flow cytometry.CONCLUSIONS: H₂O₂-induced apoptosis in myocytes was a time-and concentration-dependent process. Treatment with low concentration of H₂O₂(＜1 mmol/L) only caused cardiomyocyted early biochemical changes, such as increase of free radicals level and membrane permeability ,which were pro-apoptotic injurious features. High concentration of H₂O₂ (＞10 mmol/L) rapidly induced a necrotic form of death characterized by smeared patterns of DNA digestion on agarose gel electrophoresis and lethal membrane disruption (as measured by LDH release). Exposure of 5~10 mmol/L H₂O₂ induced cardiomyocytes apoptosis concurrently with biochemical changes of LDH and MDA increase in the medium.     

Effect of valsartan on calcium channel current and sodium-calcium exchanger current in heart failure rats

AIM: To determine the effects of valsartan on calcium channel and sodium-calcium exchanger current in isolated ventricular myocytes of congestive heart failure (CHF) rats. METHODS: Eight weeks after coronary ligation, the rats with heart failure were confirmed by measuring the hemodynamic parameters and divided randomly into the group treating with valsartan (CHF-T, 20 mg/kg) and placebo (CHF-C). Sham-operated group rats served as negative controls (PS). Twelve weeks later, 6 rats were selected randomly for the study of ion channel. Single ventricular myocytes of rats were isolated by enzymatic dissociation. The whole-cell patch-clamp recording technique was used to record calcium channel current and sodium-calcium exchanger current. RESULTS: (1) In the hemodynamic variables, HR and blood pressure were not significantly different in three groups. Compared CHF-C with PS group, LVEDP and Cm increased, LVSP and ±dp/dtmax decreased (P<005). Compared CHF-T group with CHF-C group, LVEDP and Cm decreased, LVSP and ±dp/dtmax increased (P<005). (2) Calcium channel current in CHF-C decreased significantly (P<005). Calcium channel current in CHF-T group was larger significantly than that in CHF-C group (P<005). (3) The activation, inactivation and recovery curves were not altered in 3 groups (P>005). (4) Na+-Ca2+ exchanger current in CHF-C group increased significantly. Na+-Ca2+ exchanger current in CHF-T group was smaller significantly than that in CHF-C group. However, CHF-T group and PS group were not significantly different. CONCLUSION: Administration of valsartan is effective in preventing from cardiac function deterioration, increases calcium channel current and decreases Na+-Ca2+ exchanger current in ventricular myocytes of heat failure rats.     

Transfection of rAAV1-SERCA2a improves cardiac function of beagles with heart failure

AIM:To study the effects of recombinant adeno-associated virus type 1 (rAAV1)-sarcoplasmic/endoplasmic reticulum calcium ATPase 2a (SERCA2a) transfection on the cardiac function of beagles with heart failure (HF). METHODS:The beagles were used to make an animal model with heart failure after rapid right ventricular pacing (230 beats/min) for 30 d. A reduced rate (180 beats/min) was continuously applied for another 30 d. The beagles were divided into 4 groups (n=4): control group, HF group, HF+EGFP group and HF+SERCA2a group. rAAV1-EGFP and rAAV1-SERCA2a (both 1×1012 viral genomes) were intramyocardially injected into the animals in the latter 2 groups, respectively. RESULTS:After transfection for 30 d, the left ventricular systolic function in HF+SERCA2a group was similar to that in control group, and significantly higher than that in HF group (P<0.05). The ratio of SERCA2a mRNA/GAPDH mRNA was significantly higher in HF+SERCA2a group than that in HF group (P<0.05). The expression level of SERCA2a in the myocardial tissues was higher in HF+SERCA2a group than that in HF group (P<0.05). The apoptotic index of the cardiomyocytes and the protein expression of MMP-9 were much lower in HF+ SERCA2a group than those in HF group (P<0.05). No significant difference of all parameters was observed between HF group and HF+EGFP group. The mRNA level of phospholamban was unchanged. CONCLUSION:Transfection of SERCA2a improves the expression of SERCA2a, restores the cardiac function and inhibits left ventricular remodeling by reducing the cardiac cell apoptosis and the MMP-9 expression in the heart failure beagles.     

Effects of ischemic preconditioning on oxidative stress and mitochondrial function in young and old rat myocardium with ischemia/reperfusion

AIM: To study the protective effect of ischemia preconditioning (IPC) on ischemia/reperfusion (IR)-damaged myocardium in young and old rats. METHODS: Male Wistar rats aged at 3 months (young) and 20 months (old) were used to establish myocardial IPC model and IR model with the method of Langendorff heart perfusion. The rats were divided into young ischemia/reperfusion (YIR) group, young ischemic preconditioning (YPC) group, old ischemia/reperfusion (OIR) group and old ischemic preconditioning (OPC) group. Transmission electron microscopy was used to observe the ultrastructural changes of myocardial tissue and myocardial mitochondria. The myocardial infarction area was determined by TTC staining. The lactate dehydrogenase (LDH) content in coronary effluent fluid and the levels of superoxide dismutase (SOD) and malondialdehyde (MDA) in myocardial tissues were detected by the method of colorimetry. The levels of nitrated and carbonylated proteins in myocardial tissue were measured by ELISA. The myocardial cell apoptosis was analyzed by TUNEL assay. The mitochondrial respiratory function and mitochondrial permeability transition pore opening induced by calcium load were evaluated by oxygen electrode method. RESULTS: Compared with YIR group, the myocardial infarction area in YPC group was obviously smaller, SOD activity in myocardial tissues increased, LDH activity in coronary effluent fluid and the content of MDA decreased, and the levels of nitrated and carbonylated proteins in the cardiac tissues reduced. In YPC group, the mitochondrial membrane structure appeared intact, cristae of the mitochondria showed close arrangement, and the matrix was compressed under the electron microscope. Myocardial mitochondrial respiratory control rate, state Ⅲ oxygen consumption and the P/O ratio in YIR group all significantly increased, proton leak decreased, mitochondrial swelling induced by calcium distinctly reduced, and myocardial apoptosis rate declined. No significant difference of the above indexes between OIR group and OPC group was observed. Compared with YPC group, myocardial ultrastructural damage increased clearly, cardiac oxidative stress increased, mitochondrial respiratory function declined, and cell apoptosis and necrosis increased in OPC group. CONCLUSION: Ischemic preconditioning has protective effect against myocardial IR injury in young rat hearts, while old rat hearts were less sensitive to ischemic preconditioning, leading to bluntness of cardioprotection with IPC in aging hearts. This may be related to mitochondrial injury and severe cellular apoptosis caused by increase of cardiac oxidative stress levels in the aging ischemic preconditioning heart.     

Transplantation of bcl-2 gene-modified bone marrow mesenchymal stem cells improves cardiac function and angiogenesis in rabbit ischemic car-diac insufficiency model

AIM: To investigate the effects of transplantation of bone marrow mesenchymal stem cells (BMSCs) modified by bcl-2 gene on myocardial cell apoptosis, angiogenesis and cardiac function in the rabbit after acute myocardial infarction (MI).METHODS: The rabbit BMSCs were isolated, cultured and purified in vitro. The BMSCs were transfected with adenovirus or adenovirus-Bcl-2. The rabbit model of MI was established by ligation of left anterior descending branch. The rabbits were injected with Ad-Bcl-2-BMSCs (MI+Bcl-2-BMSCs group), Ad-BMSCs (MI+BMSCs group) and DMEM (MI group) in infarction marginal zone 2 weeks after ligation. The cardiac function was evaluated by echocardiography.The apoptosis of myocardial cells was measured by TUNEL. The mRNA expression of VEGF was detected by real-time PCR. The expression of CD31 was examined by immunohistochemical staining, and new blood capillaries were counted at 4 weeks after BMSCs transplantation. The correlation of the above values with cardiac function was analyzed.RESULTS: The cardiac function was better, the apoptotic rate was lower, the mRNA expression of VEGF and the capillary density were higher in both MI+Bcl-2-BMSCs group and the MI+BMSCs group than those in MI group, and those in MI+Bcl-2-BMSCs group increased more obviously.The left ventricular ejection fraction (LVEF) had a negative correlation with the myocardial cell apoptosis rate. A positive correlation with the mRNA expression level of VEGF and the capillary density was also observed.CONCLUSION: The transplantation of BMSCs modified by bcl-2 gene significantly reduces the myocardial cell apoptosis, promotes angiogenesis, improves heart function of the rabbits with MI.     

Exercise training improves heart function through inducing autophagy and inhibitingapoptosis in aged rats

AIM：To study the mechanism of exercise training in improving old rat cardiac functions, and the effect of gradient exercise training on autophagy and apoptosis in aged rats. METHODS：The rats were randomly divided into 3 groups: young, old and old+exercise (old+Ex). Ultrasonic cardiogram was employed to determine the cardiac functions in the rats. Transmission electron microscope was applied to observe the changes of cardiomyocyte ultrastructure, autophagosome formation and mitochondrial morphology. Western blotting was used to observe the protein expression of Atg5, Beclin 1, microtubule-associated protein 1 light chain 3 (LC3) in cardiac tissues and cytochrome C (Cyt C) in the myocardial mitochondria. TUNEL was adopted to test the apoptosis and spectrophotometry was used to detect the opening of calcium-induced mitochondrial permeability transition pore (mPTP). RESULTS：(1) Compared with young group, the observation in old hearts under transmission electronic microscope found irregular arrangement in myofibrils, loose mitochondria matrix, rupture in mitochondrial membrane and mass deposition of lipofuscin granular in myofilament. In old group, the protein expression of Atg5 and Beclin 1 in the cardiac tissues decreased, the ratio of LC3Ⅱ to LC3Ⅰdropped, mitochondrial Cyt C expression declined, apoptotic index rose, and mitochondrial mPTP opening increased. Noticeable increases were found in left ventricular end-systolic diameter and left ventricular end-diastolic diameter, but left ventricular ejection fraction and left ventricular fractional shortening were decreased. (2) The ultra-structure of the hearts in old +Ex group showed clear sacromere structure, dense matrix and increased number of mitochondria, more autophagosomes and distinct decrease in lipofuscin granular deposition. In addition, the protein expression of Beclin 1 and Atg5 rose, conversion from LC3 I to LC3 II increased, apoptotic index decreased, mPTP opened less, the expression of mitochondrial Cyt C up-regulated, and a significant improvement was observed in left ventricle functions in old+Ex group as compared with old group. CONCLUSION：Exercise training may improve the heart functions in aged rat by upgrading cardiomyocyte autophagy and inhibiting cell apoptosis.     

Heat-shock protein 90-dependent translocation of Akt to mitochondria mediates insulin-like growth factor 1-induced protection of rat hearts under hypothermic preservation

AIM: To investigate the effect of insulin-like growth factor 1 (IGF-1) on hypothermic preservation of rat hearts. METHODS: Isolated rat hearts were preserved in Celsior solution with or without IGF-1 (10 nmol/L) for 9 h, followed by 60 min of reperfusion. Cell apoptosis was assessed by TUNEL method. The left ventricular developed pressure (LVDP) was recorded. Total Akt protein and phosphorylation of Akt protein were detected by Western blotting. RESULTS: Compared with Celsior solution preservation group, IGF-1 significantly enhanced the LVDP recovery rate, decreased the apoptotic index, and inhibited the opening of mitochondrial permeability transition pore. IGF-1 increased the phosphorylation of Akt in 9 h of hypothemically preserved rat heart, which was inhibited by PI3K inhibitor LY294002. LY294002 also abolished the cardioprotection of IGF-1. 17-Allylamino-17-demethoxy-geldanamycin, a heat-shock protein 90 (HSP90) inhibitor, inhibited the IGF-1-induced increase in phosphorylation level of Akt and transolation to mitochondria, the improvement of cardiac functions, and the decrease in apoptosis. CONCLUSION: IGF-1 improves the cardiac functions and decreases apoptosis in the hearts under hypothermic preservation. The mechanism might involve in HSP90-dependent translocation in Akt to mitochondria.     

Effects of insulin on cardiac fibroblast proliferation and cardiac myocyte hypertrophy

AIM:To study the effect of insulin on proliferation and hypertrophy of cardiac myocytes and its role in the induction of cardiac hypertrophy. METHODS:1. The neonatal rat cardiac myocytes and cardiac fibroblasts were cultured respectively and identified with light microscopy, electron microscopy and immunocytochemistry. 2. Cell proliferation was measured with cell number, metabolic activity and DNA synthesis (with WST-1, BrdU enzyme-linked immunosorbent assay ) and the percentage of S+G₂+M in cell cycle (by flow cytometry ). 3.Cell hypertrophy was evaluated by cell protein content (Coomassie Briliant Blue's method). RESULTS:1. The cultured cells showed the characteristic of cardiac myocytes and cardiac fibroblasts, respectively. 2. After being treated with insulin, the cell number, absorbance of BrdU incorporation and WST-1 cleavage products and the percentage of S+G₂+M of cardiac fibroblasts increased significantly (P＜0.01 orP＜0.05), while the above parameters of cardiac myocytes remained unchanged (P＞0.05). 3. Protein content of cardiac myocytes increased significantly in a dose-dependent manner (P＜0.01 orP＜0.05) in insulin treated groups (10^-10 mol/L-10^-7 mol/L). CONCLUSION:Insulin promoted cardiac fibroblast proliferation and increased myocytes protein content(induced myocyte hypertrophy)in vitroand may play an important role in pathogenesis of cardiac hypertrophyin vivo.