咪达普利与福辛普利对糖尿病大鼠心肌超微结构的影响

目的 用咪达普利(达爽)及福辛普利(蒙诺)两种血管紧张素转换酶抑制剂(ACEI)对实验性糖尿病大鼠进行早期干预,观察两药在改善糖尿病大鼠心肌超微结构方面的作用.方法 用链脲佐菌素对30只SD大鼠进行腹腔注射,建立实验性糖尿病大鼠模型.将建模成功的动物随机分为糖尿病组(9只),咪达普利干预组(9只),福辛普利干预组(10只),另外取10只SD大鼠作为正常对照组.10 w后,观察各组大鼠心肌的超微结构.结果 糖尿病组大鼠的心肌肌原纤维走行紊乱,肌节破坏断裂,长短不一,肌丝灶性溶解、消失;闰盘排列有断裂现象,线粒体肿胀变形、嵴稀疏、排列紊乱,结构不清.心肌内微血管基底膜增厚,间质胶原纤维增生.咪达普利治疗组与福辛普利治疗组心肌超微结构均有所改善,福辛普利效果更佳.结论 咪达普利和福辛普利均可延缓实验性糖尿病大鼠心肌超微结构的病理性改变,后者优于前者.     

福辛普利对SHR左室肥厚和心肌纤维化的影响

目的探讨福辛普利对自发性高血压大鼠(SHR)左心室肥厚(LVH)和心肌纤维化的影响。方法18只16周龄SHR大鼠,随机分为福辛普利治疗组(SHR-F)和SHR空白对照组(SHR-C);另设同源的WKY大鼠8只为正常对照组。治疗组口服福辛普利20mg·kg-1·d-1,给药8周后处死动物,取左心室心肌称重,计算左心室/体重比(LVW/BW),Masson三色法染色观察左心室心肌胶原变化,计算机图像分析测量心肌切片的胶原容积分数(CVF)和血管周围胶原面积(PVCA)。结果SHR空白对照组的SBP、LVW/BW、CVF、PVCA均显著高于WKY对照组(P<0.01),与SHR空白对照组相比,福新普利治疗组能有效降低SHR的SBP,改善SHR左心室肥厚(P<0.01〉并使左心室内膜及心肌小动脉周围的胶原减少(P<0.01〉。结论福辛普利可有效降低SHR血压,部分逆转心肌纤维化和左室肥厚。     

复方丹参滴丸及其与福辛普利联用对自发性高血压大鼠左室肥厚的影响

目的探讨复方丹参滴丸(DSP)及其与福辛普利联用对自发性高血压大鼠(SHR)左室肥厚的影响.方法将48只8周龄雄性SHR随机分为6组:DSP小剂量组、DSP大剂量组、福辛普利组、DSP小剂量与福辛普利联用组、DSP大剂量与福辛普利联用组、SHRs对照组.6组分别干预8周后测大鼠尾动脉收缩压;局部心肌/血浆血管紧张素Ⅱ、血浆醛固酮浓度;左室肥厚指数.结果DSP可降低血浆AngⅡ、Ald及局部心肌AngⅡ浓度(P＜0.01或P＜0.05),并可进一步增强福辛普利的这一作用;与对照组比较DSP可明显减轻左室肥厚(P＜0.01或P＜0.05),与福辛普利联用时可进一步提高后者的抗左室肥厚效应.结论DSP及其与福辛普利联用具有拮抗SHR左室肥厚作用.     

干预时间对福辛普利钠抗大鼠心肌重构作用的影响

目的研究干预时间对福辛普利钠抗大鼠心肌重构作用的影响机制。方法腹主动脉缩窄法复制压力负荷增高致大鼠心肌重构的动物模型,术后2 w存活动物分为假手术组(sham),手术组(AAC),手术+福辛普利钠早期干预组(Fosi-E),手术+福辛普利钠晚期干预组(Fosi-L),手术+福辛普利钠全程干预组(Fosi-W)。Mallory三色染色观察心肌组织内胶原纤维含量的变化,双抗体夹心ABC-ELISA法检测心肌组织内TNF-α和IL-10的表达。结果 Fosi-W组较早期及晚期干预组能明显降低心脏指数,减少心肌胶原容积分数,改善心功能。ELISA检测结果提示,AAC组心肌组织中TNF-α表达显著增多(P<0.01),IL-10无统计学差异,心肌组织内TNF-α/IL-10比例上调;Fosi-W组较早期及晚期干预组更能明显降低心肌组织TNF-α,显著升高IL-10在心肌组织中的表达,且能下调心肌组织TNF-α/IL-10比值(P<0.01)。结论福辛普利钠全程干预更能有效改善压力负荷增高所致大鼠心肌重构,其对TNF-α/IL-10的正向调控作用可能是其抗心肌重构的分子机制之一。     

复方丹参滴丸与福辛普利联用对自发性高血压大鼠左室纤维化的影响

目的　探讨复方丹参滴丸 (DSP)与福辛普利联用对自发性高血压大鼠 (SHR)左室纤维化的影响。方法　将 48只8周龄雄性SHR随机分为 6组 :DSP小剂量组 ;DSP大剂量组 ;福辛普利组 ;DSP小剂量与福辛普利联用组 ;DSP大剂量与福辛普利联用组 ;SHR对照组。 6组分别用灌胃法给药8周 ,测大鼠尾动脉收缩压、左室肥厚指数 ;局部心肌 /血浆血管紧张素Ⅱ、血浆醛固酮浓度 ;通过天狼星红染色进行心肌胶原定性和半定量分析。结果　与对照组比较 ,DSP可明显减轻左室肥厚 (P <0 .0 1) ,改善左室纤维化 (P <0 .0 1或P <0 .0 5 ) ,并与福辛普利联用时可进一步提高后者的抗心肌纤维化效应 ;DSP尤其与福辛普利联用时可降低血浆AngII、Ald及局部心肌AngII浓度 (P <0 .0 1或P <0 .0 5 )。结论　DSP与福辛普利联用可改善SHR心肌纤维化(MF)。     

福辛普利拉预处理对心肌细胞缺氧/复氧损伤的预防作用

目的:探讨福辛普利拉对培养乳鼠心肌细胞缺氧/复氧(A/R)损伤的预防作用。方法:取SD新生大鼠(1~3 d),培养成心肌细胞,在培养的第4天随机分为5组:①正常对照组,②A/R组,③0.2 mmol/L福辛普利拉预处理组(F1组),④0.6 mmol/L福辛普利拉预处理组(F2组),⑤1.8 mmol/L福辛普利拉预处理组(F3组)。分别观察各组心肌细胞搏动频率、细胞存活率、培养液中乳酸脱氢酶(LDH)活性、心肌细胞肌浆网钙泵(SERCA)mRNA的表达水平和心肌细胞内游离[Ca2 ]浓度。结果:①细胞搏动频率:A/R组比正常对照组明显减低(P<0.01);福辛普利拉各剂量组比A/R组显著加快(P<0.01),比正常对照组稍慢(P>0.05)。②细胞存活率:A/R组比正常对照组明显降低(P<0.01);福辛普利拉各剂量组比A/R组明显增高(P<0.01),而与正常对照组相比差异无统计学意义(P>0.05)。③LDH活性:A/R组比正常对照组明显升高(P<0.01);福辛普利拉各剂量组比A/R组明显降低(P<0.01),与正常对照组相比虽有升高但差异无统计学意义(P>0.05)。④SER-CA mRNA的表达水平:A/R组比正常对照组mRNA表达下调,为正常对照组的(0.78±0.30)倍(P<0.01);福辛普利拉各剂量组比A/R组显著上调(P<0.01)。⑤心肌细胞内游离[Ca2 ]浓度:A/R组比正常对照组明显升高(P<0.01);福辛普利拉各剂量组比A/R组明显降低(P<0.01),而与正常对照组相比差异无统计学意义(P>0.05)。结论:福辛普利拉预处理后对A/R心肌细胞损伤具有预防作用,其机制可能与SERCA表达上调、减轻细胞内Ca2 超载有关。     

血管紧张素转换酶抑制剂和AT1受体拮抗剂联合应用对大鼠心室重构影响的实验研究

目的　利用大鼠心肌梗死 (MI)模型 ,探讨福辛普利 (ACEI)、AT1受体拮抗剂 (依贝沙坦 )及二者合用防治心室重构的作用及机制。方法　 2 0 0 3- 0 3～ 2 0 0 3- 0 6将心肌梗死 (MI)后 2 4h大鼠随机分组。 6周后查 :平均动脉压、左室舒张末压 ;心室重量 /体重 ;非梗死区总胶原、Ⅰ型及Ⅲ型胶原所占面积的百分比及非心肌细胞增生数 ;转化生长因子 (TGF β1)mRNA表达。结果　依贝沙坦组和两药合用组总胶原含量较福辛普利组降低更明显 ;两药合用组I型胶原含量和非心肌细胞增生数低于福辛普利组。依贝沙坦组和两药合用组与安慰剂组相比TGF β1mRNA表达降低。结论　两药单独及联合应用可抑制心肌肥大及胶原沉积 ;在抑制胶原沉积上依贝沙坦及联合用药较福辛普利效果更佳 ;依贝沙坦及两药合用可使TGF β1mRNA表达降低 ;两药合用较福辛普利单用有更强的抑制非心肌细胞增生的作用。     

福辛普利对急性心肌梗死大鼠心室重构的影响

目的 观察福辛普利对急性心肌梗死大鼠心室重构的防治作用。方法 大鼠结扎左冠状动脉前降支造成急性心肌梗死,同时应用福辛普利进行治疗,给药4周后测定心室重构大鼠血液动力学、生化学及形态学参数。结果 福辛普利对急性心肌梗死心室重构大鼠,能明显升高左心室内压最大上升和下降速率(±dp/dtmax)及其校正值(±dp/dtmax/LVSP),降低左心室收缩压(LVSP)及左心室舒张末压(LVEDP),亦能明显降低左心室容积(LVV)、左心室长轴(LVLA)长度、左心室短轴(LVSA)长度、左心室绝对重量(LVAW)、左心室相对重量(LVRW)、左心室绝对重量(RVAW)和右心室相对重量(RVRW),但对心率(HR)、收缩压(SBP)、舒张压(DBP)、平均动脉压(MAP)及体重(BW)均无明显影响。此外,可明显降低血清脂质过氧化物(LPO)及心肌血管紧张素Ⅱ(Ang Ⅱ)和肾上腺素(E)含量,提高超氧化物歧化酶(SOD)及谷胱甘肽过氧化物酶(GSH-Px)活性。结论 福辛普利能有效防治急性心肌梗死大鼠的心室重构。     

伊贝沙坦联合培哚普利治疗对压力负荷性心肌肥厚大鼠心肌钙调神经磷酸酶及钙泵的影响

目的初步探讨钙调神经磷酸酶、钙泵和血管紧张Ⅱ素在大鼠压力负荷性心肌肥厚中的变化及伊贝沙坦和培哚普利联合应用对它们的影响。方法40只雄性SD大鼠随机分为5组,每组8只。除假手术组外,其余4组大鼠采用腹主动脉部分结扎法造成压力负荷性心肌肥厚模型,术后1周分别用下列药物开始灌胃:假手术组生理盐水2mL/kg.d,对照组生理盐水2mL/kg.d,伊贝沙坦组(20mg/kg.d)、培哚普利组(2mg/kg.d)及联合用药组(培哚普利2mg/kg.d,伊贝沙坦20mg/kg.d)。用药6周后测量左室质量指数(LVMI)、血浆和心肌AngⅡ、心肌钙调神经磷酸酶及钙泵活性的变化。结果联合用药组LVMI((2.14±0.12)显著低于对照组(2.99±0.16)及单用伊贝沙坦(2.36±0.13)或培哚普利组(2.39±0.16)(P<0.05),伊贝沙坦组血浆AngⅡ(伊贝沙坦:630±50.7比假手术:309±29.9,对照:310±36.8,培哚普利:288±36.9,联合用药:327±46.1,P<0.05)及心肌AngⅡ(伊贝沙坦:7.15±0.50比假手术:3.11±0.93,对照:5.04±0.35,培哚普利:3.21±0.34,联合用药:3.31±0.36,P<0.05)显著高于其他组,各用药组钙调神经磷酸酶活性显著低于对照组(假手术:0.44±0.04,培哚普利:0.51±0.05,伊贝沙坦:0.51±0.03,联合用药:0.49±0.04比对照:0.61±0.03,P<0.05),对照组心肌肌浆网钙泵活性显著降低(对照:3.6±0.69比假手术:6.85±0.88,培哚普利:4.51±0.58,伊贝沙坦:4.45±0.55,联合用药:5.63±0.61,P<0.05),联合用药组可明显增加钙泵活性至正常。相关分析显示LVMI与CaN呈显著正相关(r=0.80,P<0.01),与钙泵活性呈负相关(r=-0.726,P<0.01)。结论伊贝沙坦升高心肌AngⅡ而培哚普利对其无影响,两者均能降低心肌钙调神经磷酸酶活性,升高心肌钙泵活性,联合应用更有利于改善心肌肥厚。     

氯沙坦、福辛普利、氨氯地平对高血压大鼠心肌细胞凋亡及心肌纤维化影响的对比研究

目的评价氯沙坦、福辛普利、氨氯地平对高血压大鼠(SHR)心肌细胞凋亡、心肌纤维化及心脏重构效应.方法SHR随机分为氯沙坦组、福辛普利组、氨氯地平组和对照组.分别治疗8周、16周后对心肌细胞凋亡、心肌纤维化有关指标进行检测.结果①各治疗组治疗8周、16周收缩压显著下降,心脏重量指数及左心室重量指数显著降低,福辛普利组治疗16周较其他两治疗组左心室重量指数指标减低.②治疗8周心肌细胞凋亡指数仅福辛普利组下降,治疗16周各治疗组均下降,尤以福辛普利组明显.③治疗8周福辛普利、氯沙坦两组心肌胶原容积分数和心肌血管周围胶原面积下降;治疗16周各治疗组均下降,福辛普利组两指标较氨氯地平组下降显著,但仅前指标较氯沙坦组下降明显.④治疗8周及16周氯沙坦组血浆及心肌组织血管紧张素Ⅱ(AngⅡ)增加.治疗8周福辛普利组心肌组织AngⅡ下降,治疗16周福辛普利、氨氯地平两组组织AngⅡ均下降,前组较后组显著.结论3种药物均能有效逆转心肌肥厚及抗心肌细胞凋亡及心肌纤维化,以福辛普利作用显著,其作用与拮抗心肌组织AngⅡ效应有关.     

Melatonin ameliorates calcium homeostasis in myocardial and ischemia-reperfusion injury in chronically hypoxic rats

Chronic hypoxia (CH) leads to the deterioration of myocardial functions with impaired calcium handling in the sarcoplasmic reticulum (SR), which may be mediated by oxidative stress. We hypothesized that administration of antioxidant melatonin would protect against cardiac and ischemia-reperfusion (I/R) injury by ameliorating SR calcium handling. Adult Sprague-Dawley rats that had received a daily injection of melatonin or vehicle were exposed to 10% oxygen for 4 wk. The heart of each rat was then dissected and perfused using a Langendorff apparatus. The ratio of heart-to-body weight, ventricular hypertrophy and hematocrit were increased in the hypoxic rats compared with the normoxic controls. Malondialdehyde levels were also increased in the heart of hypoxic rats and were lowered by the treatment of melatonin. The hearts were subjected to left coronary artery ischemia (30 min) followed by 120-min reperfusion. Lactate dehydrogenase leakage before ischemia, during I/R and infarct size of the isolated perfused hearts were significantly elevated in the vehicle-treated hypoxic rats but not in the melatonin-treated rats. Spectroflurometric studies showed that resting calcium levels and I/R-induced calcium overload in the cardiomyocytes were more significantly altered in the hypoxic rats than the normoxic controls. Also, the hypoxic group had decreased levels of the SR calcium content and reduced amplitude and decay time of electrically induced calcium transients, indicating impaired contractility and SR calcium re-uptake. Moreover, there were reductions in protein expression of calcium handling proteins, markedly shown at the level of SR-Ca(2+) ATPase (SERCA) in the heart of hypoxic rats. Melatonin treatment significantly mitigated the calcium handling in the hypoxic rats by preserving SERCA expression. The results suggest that melatonin is cardioprotective against CH-induced myocardial injury by improving calcium handling in the SR of cardiomyocytes via an antioxidant mechanism.     

Cardiac-specific elevations in thyroid hormone enhance contractility and prevent pressure overload-induced cardiac dysfunction

Thyroid hormone (TH) is critical for cardiac development and heart function. In heart disease, TH metabolism is abnormal, and many biochemical and functional alterations mirror hypothyroidism. Although TH therapy has been advocated for treating heart disease, a clear benefit of TH has yet to be established, possibly because of peripheral actions of TH. To assess the potential efficacy of TH in treating heart disease, type 2 deiodinase (D2), which converts the prohormone thyroxine to active triiodothyronine (T3), was expressed transiently in mouse hearts by using the tetracycline transactivator system. Increased cardiac D2 activity led to elevated cardiac T3 levels and to enhanced myocardial contractility, accompanied by increased Ca(2+) transients and sarcoplasmic reticulum (SR) Ca(2+) uptake. These phenotypic changes were associated with up-regulation of sarco(endo)plasmic reticulum calcium ATPase (SERCA) 2a expression as well as decreased Na(+)/Ca(2+) exchanger, beta-myosin heavy chain, and sarcolipin (SLN) expression. In pressure overload, targeted increases in D2 activity could not block hypertrophy but could completely prevent impaired contractility and SR Ca(2+) cycling as well as altered expression patterns of SERCA2a, SLN, and other markers of pathological hypertrophy. Our results establish that elevated D2 activity in the heart increases T3 levels and enhances cardiac contractile function while preventing deterioration of cardiac function and altered gene expression after pressure overload.     

Improving glucose metabolism and/or sarcoplasmic reticulum Ca2+-ATPase function is warranted for immature pressure overload hypertrophied myocardium.

The cellular mechanisms of abnormal calcium regulation and excitation-contraction coupling in relation to glucose metabolism in the hypertrophied heart are not well understood. The present study evaluated the myocardial mechanics of 6-7-week-old pressure overload hypertrophied rabbit hearts in response to dobutamine by (1) serial echocardiograms in vivo and (2) isolated Langendorff perfusion. Cytosolic Ca2+([Ca2+]i) and sarcoplasmic reticulum Ca2+-ATPase (SERCA2) expression were measured by fluorescence spectroscopy and Western immunoblotting, respectively. The effect of glycolytic inhibition by 2-deoxy-D-glucose +/- pyruvate was also evaluated. Both systolic and diastolic [Ca2+]i tended to be higher and diastolic calcium removal (tauCa) significantly slower in the hypertrophied heart. The myocardial response to dobutamine was blunted and dobutamine insignificantly improved tauCa. The SERCA2 protein level was higher in early hypertrophy, but was significantly reduced by 6 weeks of age, with progressive contractile failure. Inhibition of glycolysis or SERCA2 caused an increase in [Ca2+]i as well as a slower tauCa. Pyruvate completely preserved myocardial function and [Ca2+]i handling during glycolytic inhibition. It was concluded that in this model of advanced pressure overload hypertrophy, contractile failure and inotrope insensitivity are associated with increased [Ca2+]i, slower tauCa and reduced sensitivity of the contractile proteins to Ca2+. These changes occur in association with downregulation of the SERCA2, probably caused by impaired glucose metabolism.     

Modification of cardiac subcellular remodeling due to pressure overload by captopril and losartan

In view of the activation of renin-angiotensin system under conditions associated with pressure overload on the heart, we examined the effects of captopril, an angiotensin converting enzyme inhibitor, and losartan, an angiotensin II receptor antagonist, on cardiac function, myofibrillar ATPase and sarcoplasmic reticular (SR) Ca2+-pump (SERCA2) activities, as well as myosin and SERCA2 gene expression in hypertrophied hearts. Cardiac hypertrophy was induced in rats treated with or without captopril or losartan by banding the abdominal aorta for 8 weeks; sham operated animals served as control. Decrease in left ventricular developed pressure, +dP/dt and -dP/dt as well as increase in left ventricular end diastolic pressure and increased muscle mass due to pressure overload were prevented by captopril or losartan. Treatment of animals with captopril or losartan also attenuated the pressure overload-induced depression in myofibrillar Ca2+-stimulated ATPase, myosin ATPase, SR Ca2+-uptake and SR Ca2+-release activities. An increase in beta-myosin heavy chain mRNA and a decrease in alpha-myosin heavy chain mRNA as well as depressed SERCA2 protein and SERCA2 mRNA levels were prevented by captopril or losartan. These results suggest that both captopril and losartan improve myocardial function in cardiac hypertrophy by preventing changes in gene expression and subsequent subcellular remodeling due to pressure overload.     

缺氧对心肌细胞内游离钙离子浓度和SERCA2表达的影响及薯蓣皂甙的干预作用

目的　研究缺氧对心肌细胞内游离钙离子浓度和肌浆网上的钙离子ATP酶(SERCA2 )的表达的影响及薯蓣皂甙的干预作用。方法　在离体心肌细胞培养基础上制备心肌细胞缺氧模型 ,随机分为 4组 :正常对照组 ,缺氧损伤组 ,薯蓣皂甙组 ,钙拮抗剂组。分别测定各组心肌细胞内游离钙离子的浓度 (FURA2 /AM荧光探针法 )和SERCA2的含量 (Westernblot法 )。结果　缺氧损伤组心肌细胞内游离钙离子的浓度较正常对照组明显增加 ,SERCA2的表达明显减弱 (P均 <0 0 1 ) ;薯蓣皂甙组和钙拮抗剂组心肌细胞内游离钙离子的浓度较缺氧损伤组明显降低 (P <0 0 1 ) ,SERCA2的表达明显增强 (P <0 0 5 )。结论　薯蓣皂甙通过增强肌浆网上钙泵SERCA2的表达减轻缺氧心肌细胞的钙超负荷 ,它对缺氧心肌细胞具有保护作用 ,其作用与钙拮抗剂类似。     

福辛普利、依贝沙坦及二者合用对心肌梗死后心室重塑影响的实验研究

目的：对比福辛普利、依贝沙坦及二合用对大鼠心肌梗死后心室重塑的影响。方法：通过结扎冠状动脉左前降支诱导大鼠心肌梗死，心肌梗死后24h将大鼠随机分为：（1）安慰剂组；（2）福辛普利组；（3）依贝沙坦组；（4）福辛普利＋依贝沙坦组；另设假手术组。2周后检查以下指标：（1）平均动脉压，左室舒张末压；（2）心室重量／体重；（3）非梗死区胶原含量；（4）非梗死区非心肌细胞增生数量。结果：安慰剂组与假手术组相比左室舒张末压增加（P＜0．05），且心室重量／体重、非梗死区胶原含量及非心肌细胞增生数量增加显（P＜0．01）。福辛普利组和依贝沙坦组与安慰剂组相比平均动脉压下降、心室重量／体重及非心肌细胞增生数量下降，二合用与安慰剂组比较以上指标下降显（P＜0．01）；两药单用和合用与安慰剂组相比左室舒张末压下降（P＜0．05）。两药单独和联合应用均阻止了非梗死区胶原沉积（P＜0．01，与安慰剂组相比），两个单独用药组高于假手术组（P＜0．05），而联合治疗组与假手组间无统计学差异。福辛普利组、依贝沙坦组及二合用组三间各指标差异均无统计学意义。结论：福辛普利和依贝沙坦均可限制心肌梗死后心肌肥大、抑制左室非梗死区胶原沉积和非心肌细胞增生；二合用2周未见上述作用更显。     

Transgenic rat hearts overexpressing SERCA2a show improved contractility under baseline conditions and pressure overload

OBJECTIVE: The activity of sarcoplasmic reticulum Ca(2+)-ATPase (SERCA) is reduced in the failing myocardium. Therefore, transfer of SERCA2a cDNA is considered as a therapeutical approach. The aim of this study was analysis of the long-term effect of SERCA2a overexpression in normal as well as pressure overload challenged myocardium of transgenic rats. METHODS: Independent transgenic rat lines were established expressing the rat SERCA2a cDNA specifically in the myocardium resulting in increased SERCA2a protein levels by 30-70%. Simultaneous measurements of isometric contraction and calcium transients were carried out in right ventricular papillary muscle preparations. Hemodynamic parameters were measured in hearts of unchallenged rats as well as 10 weeks after pressure overload induced by abdominal aortic banding. RESULTS: Analysis of calcium handling and contractile parameters in isolated right ventricular papillary muscles revealed significant shortening of intracellular calcium transients and half maximal relaxation times (RT(50)). Assessing myocardial contractility in working heart preparations, both transgenic rat lines revealed elevated left ventricular pressure, improved systolic and diastolic parameters, attenuated negative force-frequency relation, and a dose-dependent beta-adrenergic effect. Aortic banding resulted in reduction of left ventricular pressure and worsening of contraction and relaxation parameters with no differences in mortality in both transgenic (+dP/dt 3084+/-96 vs. 3938+/-250 mmHg/s; RT(50) 47.0+/-1.2 vs. 36.7+/-1.4 ms) and wild-type rats (+dP/dt 2695+/-86 vs. 3297+/-122 mmHg/s; RT(50) 53.0+/-1.6 vs. 44.1+/-1.4). SERCA2a overexpressing hearts revealed improved hemodynamic parameters compared to wild-type controls. Acceleration of isovolumetric relaxation characterized by the index Tau was directly correlated to SERCA2a protein concentrations. CONCLUSION: Overexpression of SERCA2a protein results in a positive inotropic effect under baseline conditions remaining preserved under pressure overload without affecting mortality. Therefore therapeutic transfer of SERCA2a may become a potential approach for gene therapy of congestive heart failure. Moreover, transgenic SERCA2a rats will be useful for studies of long-term SERCA2a overexpression in further cardiovascular disease models.     

Modification of Cardiac Subcellular Remodeling Due to Pressure Overload by Captopril and Losartan

In view of the activation of renin-angiotensin system under conditions associated with pressure overload on the heart, we examined the effects of captopril, an angiotensin converting enzyme inhibitor, and losartan, an angiotensin II receptor antagonist, on cardiac function, myofibrillar ATPase and sarcoplasmic reticular (SR) Ca²⁺-pump (SERCA2) activities, as well as myosin and SERCA2 gene expression in hypertrophied hearts. Cardiac hypertrophy was induced in rats treated with or without captopril or losartan by banding the abdominal aorta for 8 weeks; sham operated animals served as control. Decrease in left ventricular developed pressure, +dP/dt and -dP/dt as well as increase in left ventricular end diastolic pressure and increased muscle mass due to pressure overload were prevented by captopril or losartan. Treatment of animals with captopril or Icsartan also attenuated the pressure overload-induced depression in myofibrillar Ca₂₊-stimulated ATPase, myosin ATPase, SR Ca₂₊-uptake and SR Ca²⁺-release activities. An increase in β-myosm heavy chain mRNA and a decrease in α-myosin heavy chain mRNA as well as depressed SERCA2 protein and SERCA2 mRNA levels were prevented by captopril or losartan. These results suggest that both captopril and losartan improve myocardial function in cardiac hypertrophy by preventing changes in gene expression and subsequent subcellular remodeling due to pressure overload.     

Pathophysiological aspects of myocardial hypertrophy

Heart hypertrophy in response to increased workload is a complex process in which this organ adapts to the environment by increasing the muscle mass in terms of additional contractile units and formation of different types of contractile proteins (myosin isozymes). In addition, augmentation of membrane function with respect to calcium transport activities of sarcolemma and sarcoplasmic reticulum occurs at early stages of cardiac hypertrophy associated with hyperfunction of the myocardium. However, if cardiac hypertrophy is left unattended beyond a certain period, physiological hypertrophy is converted to pathological hypertrophy whereby the cardiac muscle is unable to generate an adequate amount of contractile activity. It appears that the sympathetic nervous system is activated for producing beneficial effects at early stages but an elevated level of sympathetic tone for a prolonged period could result in dysfunction of the cardiac muscle. The transition of physiological hypertrophy to pathological hypertrophy seems to be due to the occurrence of intracellular calcium overload in the myocardial cell as a consequence of defects in the membrane calcium transport systems. It is suggested that careful attention should be paid not only to removal of the stimulus responsible for cardiac hypertrophy but also to lowering sympathetic tone. Efforts should also be made to prevent the occurrence of intracellular calcium overload due to membrane defects.     

PKC-independent signal transduction pathways increase SERCA2 expression in adult rat cardiomyocytes

Catecholamines seem to play a major role in the initial response of the heart to pressure overload. The mechanisms by which alpha(1A)-adrenoceptor stimulation increases protein synthesis and subsequently cell size have been worked out in the past. However, little is known about the functional consequence of this type of hypertrophy. Recent transgenic work seems to indicate an adaptive character of this response, but mechanistic insights have yet to be established. The present study investigates whether chronic (overnight) exposure of cardiomyocytes to phenylephrine, an alpha-adrenoceptor agonist, modifies the expression of calcium-handling proteins and identifies key elements of signal transduction pathways leading to such alterations. Cardiomyocytes exposed to phenylephrine had elevated expression of SR-calcium ATPase (SERCA), but not of the sodium-calcium exchanger (NCX). SERCA induction persisted in the presence of protein kinase C (PKC) inhibitors, but required an increase in diastolic cell calcium levels via activation of the sodium-proton exchanger (NHE) and the reverse mode of the NCX. Downstream of an increase in resting cell calcium concentrations an activation of the calcineurin/NFAT pathway was found to be responsible for SERCA2 induction. Transfection of cardiomyocytes with decoys directed against NFAT activity inhibited the increase in SERCA2 expression. Decoys did not inhibit the concomitant PKC-dependent increase in hypertrophic growth. In the absence of SERCA up-regulation, hypertrophied cardiomyocytes were unable to maintain normal, load-free cell shortening. In conclusion, our data give mechanistic insights into the adaptional process during alpha-adrenoceptor-dependent myocardial hypertrophy.