If current mediatesβ-adrenergic enhancement of heart rate but not contractility in vivo

Background: The hyperpolarization-activated I_f current in the sinoatrial (SA) node participates in the spontaneous diastolic depolarization responsible for pacemaking function. Both sympathetic and parasympathetic control of heart rate is thought to involve modulation of I_f. This study tested whether -adrenoceptor activation of heart rate, but not contractile state, could be reduced by blockade of I_f channels in the intact, anesthetized pig.Methods: Both isopterenol (ISO, 0.1 g/kg/min i.v. for 5 min) and norepinephrine (NE, 0.3 g/kg/min i.v. for 5 min) were used sequentially to activate -adrenoceptors in five metomidathydrochloride-anesthetized pigs. Left ventricular pressure and dP/dt, aortic blood pressure and cardiac output were measured. I_f channels were then blocked selectively with 0.3 mg/kg i.v. zatebradine (ULFS49) and the test doses of ISO and NE were repeated. Following a further high dose (10 mg/kg, i.v.) of zatebradine, the test doses of ISO and NE were repeated once again.Results: Before I_f blockade, ISO and NE elicited reproducible increases in both heart rate and left ventricular dP/dt. Whereas NE caused an increase in both systolic (56%) and diastolic (53%) aortic pressure and a modest heart rate increase (22%), ISO caused a decrease in diastolic aortic pressure (–22%) and a marked increase in heart rate (81%). Low dose zatebradine reduced basal heart rate from 98±6 to 66±3 bpm, p<0.05; cardiac output fell by 20%, stroke volume increased by 18% and total peripheral resistance was unchanged. ISO after low-dose zatebradine still elicited marked increases in heart rate (66±3 to 105±5 bpm, p<0.05) and left ventricular dP/dt (774±94 to 3364±206 mmHg/s, p<0.05) and reduced aortic diastolic pressure (37 ±2 to 33±1 mmHg, p<0.05). NE after low-dose zatebradine increased heart rate (73±4 to 89±5 bpm, p<0.05), left ventricular dP/dt (810 ±95 to 3372±196 mmHg/s, p<0.05) and both systolic and diastolic aortic pressures. High dose zatebradine caused no further reduction in heart rate (77±4 vs 82±6 bpm, NS) but left ventricular dP/dt decreased (798 ±92 to 418±50 mmHg/s, p<0.05) as did both systolic and diastolic aortic pressures. Subsequent administration of ISO had no effect on heart rate but increased left ventricular dP/dt from 418±50 to 3468±256 mmHg/s (p<0.05) and systolic aortic pressure increased from 58±7 to 90 ±3 mmHg (p<0.05). NE administered after high dose zatebradine also increased left ventricular dP/dt (580±54 to 2608±182 mmHg/s, p<0.05) while heart rate fell (86±4 to 74±6 bpm, p<0.05). Both systolic and diastolic aortic pressures mereased substantially during the NE infusion after high dose zatebradine.Conclusion: Zatebradine dosedependently inhibits -adrenoceptormediated heart rate increases while leaving -adrenoceptor-mediated increases in myocardial contractile state intact. This observation can be explained by a selective blockade of the hyperpolarization-activated current I_f by low concentrations of the drug.     

孟鲁司特钠对大鼠异丙肾上腺素心肌坏死的保护作用

 目的观察白三烯受体拮抗剂孟鲁司特钠对大鼠心肌坏死的保护作用。方法大鼠皮下注射异丙肾上腺素(2 mg·kg^-1)造成心肌坏死模型，ig给予孟鲁司特钠，测定血清AST，LDH，CK，MDA含量，心肌NO含量和坏死心肌面积。结果大鼠预先给予孟鲁司特钠10.0，30.0 mg·kg^-1，可以降低血清LDH，CK，MDA含量，减少心肌坏死面积。孟鲁司特钠30.0 mg·kg^-1还能促进心肌NO释放。结论孟鲁司特钠对大鼠异丙肾上腺素心肌坏死具有保护作用，有进一步研制成心肌缺血治疗药物的可能。     

多非替利衍生物CPU 228(V03)对大鼠心室肌细胞钙瞬变的调节

目的在β-受体激动情况下,研究多非替利衍生物CPU 228对电刺激触发心肌细胞的胞浆Ca2+浓度([Ca2+]i)变化及钙瞬变动力学参数的影响.方法游离单个大鼠心室肌细胞,Fluo-3/AM负载,电刺激诱发心室肌细胞钙瞬变,定量测定心室肌细胞内Ca2+浓度变化,异丙肾上腺素(isoproterenol, ISO)100nmol·L-1激动β-受体,观察CPU 228 1 μmol·L-1对钙瞬变动力学参数、[Ca2+]i及钙负荷水平的影响.结果CPU 228 1 μmol·L-1对大鼠心室肌细胞[Ca2+]i的影响不明显(P>0.05);ISO 100 nmol·L-1显著升高大鼠心室肌细胞[Ca2+]i和细胞内钙负荷水平,缩短钙瞬变时程,并且增加钙瞬变的消除速率.CPU 228 1 μmol·L-1显著抑制ISO的上述作用.结论在β-受体激动情况下,CPU 228可以降低心肌细胞[Ca2+]i,使ISO改变的钙瞬变动力学参数恢复到正常水平.     

κ-阿片受体与β1-肾上腺素受体交互作用抑制异丙肾上腺素诱导的心肌肥大

目的:观察选择性kappa阿片受体(kappaopioidreceptor,κOR)与β肾上腺素受体(βadrenergicreceptor,βAR)在心肌细胞肥大方面的交互作用。方法:以体外培养的乳鼠心肌细胞为模型,10μmol·L-1的异丙肾上腺素(β肾上腺素受体激动剂,βAR)诱导心肌肥大,观察1μmol·L-1的U50,488H(κOR激动剂,U50)对其作用。进一步探索在100nmol·L-1ICI118,551(β2AR阻断剂)存在情况下,κOR的激活对心肌肥大的作用。用Lowry’s法测心肌细胞的蛋白质含量;用消化分离法,并利用计算机图象分析系统测心肌细胞的体积;用[3H]leucine掺入法测定心肌细胞蛋白的合成。结果:异丙肾上腺素使心肌细胞总蛋白含量、体积、蛋白合成明显增加;1μmol·L-1的U50,488H使ISO诱导的心肌细胞总蛋白含量、体积、蛋白合成减少,这种作用可被选择性κOR阻断剂norBNI(norbinaltorphimine)抑制。在ICI118,551存在的情况下,U50也能起到减弱ISO诱导心肌细胞肥大的作用。结论:U50,488H通过激活κOR与β1AR交互作用抑制ISO所诱导的心肌细胞肥大。     

羟苯氨酮对实验性心肌缺血的治疗作用

目的研究强心扩血管新药羟苯氨酮(oxyphenamone)对心肌缺血的治疗作用。方法用多导生理记录仪和电磁流量计测定心脏血流动力学参数，观察药物对阻断冠脉致急性心肌梗死猫心脏生理功能的影响。形成异丙肾上腺素致大鼠心肌缺血坏死模型，从心肌酶学及病理形态学方面评价药效。结果羟苯氨酮(2-8 mg·kg^-1,iv)可剂量依赖性地降低心梗猫的心率、血压、血管阻力与张力时间指数(TTI)，轻度增加心肌收缩力与心输出量，不影响左室压与心脏作功。羟苯氨酮(4-8 mg·kg^-1,ip)可明显减轻异丙肾上腺素致大鼠心肌肌酸磷酸激酶(CPK)、丙二醛(MDA)与血清谷草转氨酶(GOT)活性变化与病理形态学损伤。结论羟苯氨酮对心肌缺血性损伤有明显治疗作用。     

Effect of Enalapril Treatment on the Heart of Normal Rats

Previous experiments showed that enalapril (EN) treatment as well as enalaprilic acid, when added to the perfusion bath, diminish the inotropic response of the papillary muscles to isoproterenol (ISO). The main objective of this study was to evaluate, in normal rats, the effect of EN on basal contractility and inotropic response to ISO on the whole perfused ventricles (Langendorff preparation). Blood pressure (BP), increase in body weight (IBW), ventricular weight/body weight ratio (R) and concentration of ventricular proteins and DNA were also analyzed. Five groups were studied: EN10: 5 mg/kg/day, 10 days; EN21(L): 5mg/kg/day, 21 days; EN21(H): 15 mg/kg/day, 21 days. C10 and C21 were untreated controls. Cardiac contractility was evaluated by the maximal developed pressure, maximal rate of rise of pressure and maximal velocity of relaxation; no changes were found due to EN treatments either on basal conditions or on ISO stimulation. Significant differences (p<0.05 vs C21) were: lower BP and R in EN21(L) and EN21(H), slower IBW in EN21(H), decreased ventricular DNA in EN21(H). In conclusion, daily treatment for ten or twenty one days with enalapril does not change either basal cardiac contractile performance or inotropic response to ISO in the Langendorff preparation. Longterm treatment with EN seems to modify nuclear processes involved in cardiomyocite DNA content     

红景天对异丙肾上腺素(ISO)致大鼠急性心肌缺血的保护作用

 目的  研究中药红景天(Rhodiola Rosea,R)对异丙肾上腺素(isoproternol,ISO)致大鼠急性心肌缺血的保护作用并初步探讨其机制。方法  SD雌性大鼠28只,随机分为4组,每组7只:正常对照组(N组);ISO模型组(ISO组);红景天保护组(R组);普萘洛尔(propranolol,PRO)阳性对照组(PRO组)。采用皮下注射ISO的方法建立大鼠急性心肌缺血模型。观察各组心电图改变、血流动力学参数(LVSP、LVEDP、±dp/dt max)的变化,测量各组心肌缺血面积(myocardial ischemia area,MIA),并检测血清超氧化物歧化酶(superoxide dismutase,SOD)活力。结果  ISO组心电图J点改变大于N组(P<0.05);与ISO组相比,R组的±dp/dt max有明显升高(P<0.05),MIA明显减少(P<0.05),SOD活力明显升高(P<0.05)。结论  红景天对ISO致大鼠急性心肌缺血具有保护作用,该作用可能与清除受损心肌细胞内自由基有关。     

裙带菜多糖保护异丙肾上腺素诱导的心脏纤维化研究

目的：探讨裙带菜多糖在异丙肾上腺素（ISO）诱导的心脏纤维化中的作用。方法将40只C57BL／6J小鼠随机分为对照组、ISO组、ISO＋裙带菜多糖组、裙带菜多糖组。ISO组连续皮下注射ISO 14 d（前3 d 10 mg·kg－1·d－1,后11 d 5 mg· kg－1·d－1）,ISO＋裙带菜多糖组除做上述ISO处理外,ISO处理前7 d开始给予裙带菜多糖200 mg·kg－1·d－1灌胃,持续到ISO皮下注射第14天;裙带菜多糖组连续21 d裙带菜多糖200 mg·kg－1·d－1灌胃;对照组以生理盐水代替ISO皮下注射。心脏超声检测各组小鼠心功能的改变,病理染色检测心脏纤维化程度,实时定量PCR检测转化生长因子-β（TGF-β）、Ⅰ型胶原α（CollagenⅠα）和Ⅲ型胶原（CollagenⅢ）的mRNA表达量的变化,Western Blot检测各组小鼠心脏自噬的改变。结果裙带菜多糖明显改善心功能,减少ISO诱导的心脏纤维化程度,心脏胶原蛋白CollagenⅠα和CollagenⅢ的mRNA表达量比ISO组显著降低（P＜0．05）,且裙带菜多糖能减少ISO诱导的心脏自噬。结论裙带菜能减轻ISO诱导的心脏纤维化,其主要是通过降低ISO诱导的心脏自噬而发挥作用的。     

左旋卡尼汀对异丙肾上腺素致心肌损害的影响

目的:观察左旋卡尼汀对异丙肾上腺素致心肌损害的保护作用并探讨其机制。方法:采用大鼠皮下注射异丙肾上腺素造成心肌损害模型。心肌切片,HE染色,光镜下观察心肌损害程度;分离心肌线粒体,测定膜脂流动性（LFU）。结果:注射左旋卡尼汀可减轻心肌损害程度;改善线粒体的损伤,改善LFU。结论:左旋卡尼汀能减轻异丙肾对心肌的损害,对线粒体膜脂流动性损伤具有明显的保护作用。     

Effects of Repeated Administration of Pilocarpine and Isoproterenol on Aquaporin-5 Expression in Rat Salivary Glands

Aquaporins are water channel proteins which enable rapid water movement across the plasma membrane. Aquaporin-5 (AQP5) is the major aquaporin and is expressed on the apical membrane of salivary gland acinar cells. We examined the effects of repeated administration of pilocarpine, a clinically useful stimulant for salivary fluid secretion, and isoproterenol (IPR), a stimulant for salivary protein secretion, on the abundance of AQP5 protein in rat salivary glands by immunofluorescence microscopy and semi-quantitative immunoblotting. Unexpectedly AQP5 was decreased in pilocarpine-administered salivary glands, in which fluid secretion must be highly stimulated, implying that AQP5 might not be required for fluid secretion at least in pilocarpine-administered state. The abundance of AQP5, on the other hand, was found to be significantly increased in IPR-administered submandibular and parotid glands. To address the possible mechanism of the elevation of AQP5 abundance in IPR-administered animals, changes of AQP5 level in fasting animals, in which the exocytotic events are reduced, were examined. AQP5 was found to be decreased in fasting animals as expected. These results suggested that the elevation of cAMP and/or frequent exocytotic events could increase AQP5 protein. AQP5 expression seems to be easily changed by salivary stimulants, although these changes do not always reflect the ability in salivary fluid secretion.