一氧化氮在铁诱导的大鼠心肌损伤中的作用

采用Langendorff灌流大鼠心脏和酶解分离的心肌细胞为实验模型,研究铁负荷下心肌损伤情况以及一氧化氮（NO）在铁诱导的心肌损伤中的地位。结果显示:（1）心肌铁负荷（Fe-HQ）可使分离心肌细胞舒张期细胞长度缩短、收缩幅度和速度降低,离体灌流心脏左室发展压（LVDP）、±dp/dtmax、冠脉流量呈现双相变化;冠脉流出液中乳酸脱氢酶（LDH）、肌酸激酶（CK）释放量和心肌丙二醛（MDA）增高。（2）NO的前体L-精氨酸（L-argi-nine,L-Arg）引起心肌细胞舒张期细胞长度缩短、收缩幅度降低。离体灌流心脏LVDP、冠脉流量、和±dp/dtmax增高,用K-H液复灌后可恢复正常。（3）L-Arg预处理,再行Fe-HQ灌流,与单纯的L-Arg或Fe-HQ组相比,心肌细胞舒张期细胞长度、收缩幅度和速度减小;离体灌流心脏LVDP、±dp/dtmax、心率和冠脉流量明显下降,冠脉流出液中LDH、CK增加。（4）Nω-硝基-L-精氨酸甲酯（L-NAME）和Fe-HQ合并灌流后,与单纯Fe-HQ组相比,心肌细胞舒张期细胞长度、收缩幅度和速度增加。L-NAME可阻断Fe-HQ引起的LVDP、左室舒张末压（LVEDP）和±dp/dtmax降低,冠脉流出液中LDH、CK增高。（5）用Triton X-100短暂处理以去除冠脉内皮后,与保留冠脉内皮的心肌相比,Fe-HQ引起的LVDP和±dp/dtmax的一过性增高现象被抑制,但     

Catecholamine sulfates: end products or metabolic intermediates?

Dopamine-beta-hydroxylase catalyzes the beta-oxidation of dopamine to noradrenaline while phenylethanolamine-N-methyltransferase converts noradrenaline to adrenaline. Since catecholamine sulfates represent the predominant form of catecholamines in human tissues, we have studied the role of dopamine sulfate and noradrenaline sulfate as alternate substrates for dopamine-beta-hydroxylase and phenylethanolamine-N-methyltransferase, respectively. Dopamine 3-sulfate, dopamine 4-sulfate and noradrenaline 3-sulfate were chemically synthesized and exhaustively purified by ion-exchange chromatography. Dopamine-beta-hydroxylase and phenylethanolamine-N-methyltransferase were partially purified from human adrenals. Using tyramine as substrate, dopamine-beta-hydroxylase is slightly inhibited by dopamine 3-sulfate according to some irreversible or mixed mechanisms. When dopamine-beta-hydroxylase was incubated with dopamine 3-sulfate or dopamine 4-sulfate, we were not able to find any synthesis of either noradrenaline sulfate or free noradrenaline. Using phenylethanolamine as substrate, the enzymatic activity of phenylethanolamine-N-methyltransferase remains unchanged with addition of dopamine 3-sulfate, dopamine 4-sulfate or noradrenaline 3-sulfate. It was concluded that dopamine sulfate is not an alternate substrate for either dopamine-beta-hydroxylase or phenylethanolamine-N-methyltransferase nor is noradrenaline 3-sulfate an alternate substrate for phenylethanolamine-N-methyltransferase.     

β(2)-adrenoreceptor mediates the cardioprotection of ischemic preconditioning on myocardial contraction in rats subjected to ischemia/reperfusion injury

The aim of the present study is to investigate the role of beta(2)-adrenoreceptor (beta(2)-AR) in ischemic preconditioning (IP) in isolated rat heart model of ischemia/reperfusion (I/R). Sprague-Dawley rat hearts were quickly removed, mounted on Langendorff apparatus, and perfused with Krebs-Henseleit (KH) solution. After the initial stabilization period, the rats were randomly divided into 6 groups including control group (perfused for an additional 20 min), IP group (4 cycles of 5 min of ischemia followed by 5 min of reflow), isoproterenol (ISO) group (10 nmol/L ISO perfusion for 5 min followed by 5 min washout), IP + ICI118551 group (55 nmol/L ICI118551 perfusion for 5 min before and throughout IP), ISO + ICI118551 group (55 nmol/L ICI118551 perfusion for 5 min before and throughout ISO treatment), ICI118551 group (55 nmol/L ICI118551 perfusion for 20 min). After these treatments, all hearts were followed by 30 min of no-flow ischemia and 30 min of reperfusion. A computer-based electrophysiological recorder system was used to measure changes of the maximal rate of pressure increase in systole phase (+dp/dt(max)), maximal rate of pressure decrease in diastole phase (-dp/dt(max)), and difference of left ventricular pressure (DeltaLVP). Then cardiomyocytes from these hearts were isolated by 5 min of Ca(2+)-free buffer perfusion and 25 min of collagenase perfusion. The ventricles were chopped and filtered. The myocytes were resuspended in KB buffer. The contraction and the viability of cardiomyocytes were measured. Lactate dehydrogenase (LDH) concentration in coronary effluent was assayed with assay kit. The results showed that both IP and ISO significantly increased the values of +/-dp/dt(max), DeltaLVP, the contraction and viability of cardiomyocytes, shortened the time-to-peak contraction (TTP), and decreased the release of LDH in coronary effluent. ICI118551, a selective beta(2)-AR antagonist, blocked these effects. Either the time-to-50% relaxation (R(50)) or the time-to-100% relaxation (R(100)) had no significant differences between groups. Our results indicate that the cardioprotection of IP was mediated by beta(2)-AR in isolated rat hearts subjected to I/R injury.     

Changes in plasma free and sulfoconjugated catecholamines before and after acute physical exercise: experimental and clinical studies.

To elucidate whether sulfoconjugated catecholamines in plasma, especially dopamine, serve as a source of free catecholamines, we examined the change in afterload on the deconjugating activity of catecholamines in isolated Langendorff perfused rat hearts. Dopamine-sulfate was administered under ordinary or high-work-load conditions. Free dopamine in the effluent was increased by the high-work-load of the hearts, whereas conjugated dopamine showed an apparent decrease. These results indicate the possibility that deconjugation of sulfoconjugated catecholamines is accelerated by a high-work-load. To obtain further evidence in humans, we also examined the changes in the plasma levels of free and sulfoconjugated catecholamines in healthy volunteers before and after marathon running. Free dopamine increased 1.99-fold from the baseline value after exercise, whereas conjugated dopamine decreased by 12%. Similarly, the plasma levels of free noradrenaline and adrenaline increased after exercise to 2.45- and 1.51-fold their respective baseline values, while conjugated noradrenaline and adrenaline both decreased. These clinical results, as well as those of the experimental studies, suggest that the increase in plasma free catecholamines after exercise is due not only to increased release from the sympathoadrenal system but also to accelerated conversion from sulfoconjugated catecholamines in the plasma.     

Isomer specific kinetics of dopamine beta-hydroxylase and arylsulfatase towards catecholamine sulfates

Both isomers of epinephrine sulfate were synthesized, unequivocally identified by 1H-NMR and highly purified from catecholamines (less than 90 ppm). Bacterial as well as pig liver arylsulfatase A and B demonstrated a higher substrate turnover of epinephrine-4-sulfate, norepinephrine-4-sulfate and dopamine-4-sulfate as compared to the 3-sulfate isomers. The arylsulfatase B however, is less important for the deconjugation of these sulfoconjugates than arylsulfatase A. Since arylsulfatase A occurs in most human tissues, it might be of physiological significance in the deconjugation of the catecholamine sulfate isomers. Furthermore the kinetic data at pH 7.4 and 6.9 suggest the increased cleavage of the sulfate group, e.g. during exercise-induced acidosis. In contrast to results reported in the literature, dopamine sulfates were no substrates of dopamine beta-hydroxylase.     

Divergent changes in the rate of development of pressure in the left ventricle and in the performance of the heart as a pump.

Dog hearts were prepared in situ so that heart rate (HR), left ventricular end diastolic pressure (LVEDP) and mean aortic pressure (MAP) could be controlled separately during computation of left ventricular dP/dt max and external stroke work (SW). Progressive increases in HR consistently raised dP/dt max over a wide range, and consistently lowered SW except at low rates. Progressive increases in LVEDP or MAP consistently raised both dP/dt max and SW. Infusion of noradrenaline consistently raided both dP/dt max and SW, except at very high HR when only dP/dt max was consistently raised. Our results lead us to question the validity of equating changes in pre-ejection measurements with changes in performance of the heart as a pump under abnormal conditions and in the assessment of inotropic agents.     

尾加压素Ⅱ对正常及缺血-再灌注离体大鼠心脏的影响

在正常Langendorff灌流与缺血-再灌注(停灌20 min-复灌20 min)离体大鼠心脏模型,观察尾加压素Ⅱ(urotensin Ⅱ,UⅡ)对冠脉流量、心功能和心肌代谢的影响以及心肌UⅡ受体的功能,以探讨UⅡ的心脏效应。对正常心脏给予0.1、1和10 nmol/L UⅡ各5 min,然后换洗5 min,对停灌缺血-再灌注心脏在再灌注期给予1或10nmol/L UⅡ。监测心率、左室内压和左室内压升降的最大变化率等心功能指标,计算冠脉流量,测定冠脉流出液中总蛋白和肌红蛋白含量以及乳酸脱氢酶(LDH)活性。灌流结束后,测定心肌丙二醛(MDA)含量和质膜UⅡ结合位点(放射性配基结合法)。结果如下:(1)正常心脏灌流UⅡ后,冠脉流量和心功能呈浓度依赖下降,换洗后没有完全恢复。心肌蛋白、肌红蛋白和LDH漏出随UⅡ浓度的增加而增加,换洗后迅速减少。UⅡ组心肌MDA含量与对照组差异无显著性。(2)缺血-再灌注后,冠脉流量显著减少,心功能显著抑制,再灌注期心肌蛋白、肌红蛋白和LDH明显漏出;给予UⅡ后,上述变化增强,且高浓度组更强,与对照组差异有显著性(P<<0.01),再灌注后心肌MDA含量亦显著高于对照(P<0.01)。(3)缺血-再灌注心肌质膜UⅡ受体的B_(max)显著高于正常对照心肌(14.65±1.78vs20.53±1.98 fmol/mg pr,P<0.01),Kd值变化无统计学意义。上述结果表明,在正常     

Adenosine A(2a)-receptor activation increases contractility in isolated perfused hearts

Adenosine A(2a)-receptor activation enhances shortening of isolated cardiomyocytes. In the present study the effect of A(2a)-receptor activation on the contractile performance of isolated rat hearts was investigated by recording left ventricular pressure (LVP) and the maximal rate of LVP development (+dP/dt(max)). With constant-pressure perfusion, adenosine caused concentration-dependent increases in LVP and +dP/dt(max), with detectable increases of 4.1 and 4.8% at 10(-6) M and maximal increases of 12.0 and 11.1% at 10(-4) M, respectively. The contractile responses were prevented by the A(2a)-receptor antagonists chlorostyryl-caffeine and aminofuryltriazolotriazinyl-aminoethylphenol (ZM-241385) but were not affected by the beta(1)-adrenergic antagonist atenolol. The adenosine A(1)-receptor antagonist dipropylcyclopentylxanthine and pertussis toxin potentiated the positive inotropic effects of adenosine. The A(2a)-receptor agonists ethylcarboxamidoadenosine and dimethoxyphenyl-methylphenylethyl-adenosine also enhanced contractility. With constant-flow perfusion, 10(-5) M adenosine increased LVP and +dP/dt(max) by 5.5 and 6.0%, respectively. In the presence of the coronary vasodilator hydralazine, adenosine increased LVP and +dP/dt(max) by 7.5 and 7.4%, respectively. Dipropylcyclopentylxanthine potentiated the adenosine contractile responses with constant-flow perfusion in the absence and presence of hydralazine. These increases in contractile performance were also antagonized by chlorostyryl-caffeine and ZM-241385. The results indicate that adenosine increases contractile performance via activation of A(2a) receptors in the intact heart independent of beta(1)-adrenergic receptor activation or changes in coronary flow.     

Blood pressure and cardiac tissue responses to prostacyclin (PGI2) in various species

The effect of prostacyclin (PGI2) on blood pressure and heart rate (in vivo) and on isolated heart tissue has been investigated in different species. Isolated cardiac tissue had limited responses to PGI2 tested at 10(-13) to 10(-5) M. Cultured neonatal rat heart cells did not respond to PGI2, neither did intact rat hearts or rabbit cardiac tissue. Guinea pig and rat atria showed limited dose-dependent responses to PGI2 at concentrations greater than 10(7) M. In rat atria, 10(-5) M PGI2 produced a limited elevation of tissue cAMP content. When given by intravenous injection or infusion, PGI2 produced hypotension in anaesthetized primates (three species), rat, rabbit, pig, and dog. As a vasodepressor in all species, PGI2 (on a weight basis) was more active than prostaglandins of the B or E type and, in most species tested, it was approximately five times more active than PGE2. Heart responses in intact animals were often paradoxical in that decreases in heart rate often accompanied blood pressure falls.     

Changes in biomechanical parameters during heart perfusion and after midazolam pre-medication--experimental pilot study

Background: Midazolam is a frequently used benzodiazepine in anaesthesiology and intensive care. Aim: The aim of pilot study was to monitor its effect during heart perfusion in the laboratory rat. Methods: The same groups of animals (n = 10). The 1(st) group was treated with midazolam in a dose of 0.5mg/kg i.p. The 2(nd) group was a placebo. After i.p. administration of heparine injection of 500 IU dose, the hearts were excised and perfused (modified Langendorf's method). Working schedule: stabilization/ischaemia/reperfusion proceed at intervals of 20/30/60 min. Monitored parameters in isolated heart: left ventricle pressure (LVP), end-diastolic pressure (LVEDP), contractility (+dP/dt(max)). Results: The treated hearts showed improved postischemic recovery, reaching LVP values of 92 +/- 6 % at the end of the reperfusion, placebo only 61 +/- 7 %. In placebo hearts LVEDP rose from 10.0 +/- 0.5 mmHg to 43 +/- 4 mmHg after, in treated animals only about 25 mmHg. The treated hearts improved +dP/dt(max) recovery during reperfusion to 91 +/- 8 %. These values were significantly greater than those obtained from the placebo hearts. Conclusions: Positive changes in monitored parameters were found in this experimental pilot study. We conclude that the administration of midazolam in laboratory rats has a cardioprotective potential against ischemia-reperfusion induced injury.     

Proteins released from liver after ischaemia induced an elevation of heart resistance against ischaemia-reperfusion injury: 2. Beneficial effect of liver ischaemia in situ

We have shown earlier that proteins released from the heart during preconditioning may protect non-preconditioned heart during sustained ischaemia, similarly as preconditioning itself. In other our experiments we have documented that also proteins released from isolated rat liver during reperfusion after global ischaemia performed a protective effect on isolated rat heart against ischaemia-reperfusion injury. In the current study we examined the effect of liver ischaemia in situ on resistance of rat heart to ischaemia and reperfusion injury. Wistar rats (male) were subjected to liver ischaemia maintained by occlusion of portal vein and hepatic artery for 20 min, followed with 30-min reperfusion after reopening of both vessels. Then the hearts were isolated and perfused according to Langendorf. Hearts, after initial stabilisation (15 min), were subjected to 20-min ischaemia and 30-min reperfusion. During reperfusion, the haemodynamic parameters of hearts were measured. The protein pattern of high soluble fraction (HS fraction) isolated from rat blood by precipitation with ammonium sulphate was detected by SDS-PAGE. Our results showed improved parameters of pressure and contractility in the group after liver ischaemia (ischaemic group), presented by decreased diastolic pressure and increased LVDP((S-D)) in comparison with levels of these parameters in the control group. We also observed improved heart contraction-relaxation cycles parameters (dP/dt)(max) and (dP/dt)(min) in ischaemic group as compared with the control group. On the other hand, there were no significant differences in heart rate and coronary flow between both experimental groups. SDS-PAGE showed changed protein pattern in HS fraction, particularly the levels of several low molecular weight proteins increased. We conclude that liver ischaemia induced a higher resistance of heart against ischaemia-reperfusion injury. We propose that release of some cardioprotective proteins present in HS fraction can also contribute to this cardioprotection.     

Effects of l-DOPA on the Concentrations of Free and Sulfoconjugated Cathecholamines in Plasma, Cerebrospinal Fluid, Urine, and Central and Peripheral Nervous System Tissues of the Rat

The effects of subcutaneous injection of L-beta-3,4-dihydroxyphenylalamine (L-DOPA) on the concentrations of the catecholamines and catecholamine sulfates in the central and peripheral nervous systems of the rat were studied. The results showed that free 3,4-dihydroxyphenylethylamine (DA, dopamine) increased rapidly and markedly in the hypothalamus and striatum after L-DOPA but DA sulfate did not change. Increased concentrations of DA sulfate were detected in the CSF and in the plasma, where it reached a concentration of 130.8 +/- 12.8 ng/ml at 2 h, seven times the level of free DA (19.1 +/- 2.9 ng/ml). In the kidney the ratio of DA sulfate to free DA was reversed in favor of free DA. Urine samples of L-DOPA-treated rats showed a higher increase of free DA than DA sulfate, but free norepinephrine (NE) and NE sulfate remained unchanged. Concentrations of free DA and free NE in the adrenal glands of L-DOPA-treated rats showed no change. Adrenal DA sulfate and NE sulfate were not detectable in the control and L-DOPA-treated rats, suggesting that the adrenal glands lack the capacity to take up or store catecholamines and their sulfate counterparts from the plasma.     

二氮嗪在长时程心脏低温保存中的作用

延长心脏的体外有效保存时间对临床心脏移植具有重要意义。本文旨在研究线粒体ATP敏感性钾通道开放剂二氮嗪(diazoxide,DE)在离体大鼠心脏长时程低温保存中的作用。SD大鼠随机分成5组,包括对照组(单纯Celsior保存液),DE组(Celsior液中含15、30或45μmol／L的DE)和DE 5-HD组[Celsior液中含30μmol／L的DE和100μmol／L的5-羟基葵酸盐(5-hydroxydecanoate,5-HD)]。利用Langendorff离体鼠心灌注法,观察心脏在4℃条件下保存10h后,复灌期血流动力学恢复、冠脉流出液中心肌酶漏出量及心肌水含量变化,并做心肌超微结构检查。结果显示：与对照组比较,DE处理后,复灌期的左心室舒张末期压力明显降低,心率、左心室发展压、左心室压力变化率、冠脉流出量等的恢复率在多个复灌时间点上优于对照组,且能显著减少复灌过程中心肌酶(乳酸脱氢酶、磷酸肌酸激酶及谷草转氨酶)的漏出量,降低心肌水含量;其中30和45μmol／LDE组的保护作用优于15μmol／LDE组;电镜结果显示DE对长时程低温保存心脏的超微结构有较好的保护作用。DE的上述作用可被线粒体ATP敏感性钾通道的特异性阻断剂5-HD所取消。以上结果提示：DE可通过激活线粒体ATP敏感性钾通道显著改善离体大鼠心脏长时程低温保存效果。     

The effect of changes in cardiac frequency on left and right ventricular dP/dt max at different contractile states of the myocardium

In 17 canine heart-lung preparations the dependence of frequency potentiation of the right and left ventricular myocardium on the basic inotropic state of the heart was investigated. The effect of unipolar stimulation of the right atrium on dP/dt max in both ventricles was measured. The aortic pressure was maintained constant. Shortly after isolation of the heart, a stepwise increase of rate from 140 to 200 beats/min only had a very weak influence on left ventricular dP/dt max. With deterioration of the myocardium the frequency potentiation of dP/dt max increased considerably. End-diastolic pressure regularly decreased with rising cardiac frequency. Since the real positive inotropic effect is masked by the concomitant fall in diastolic loading, the end-diastolic pressure was maintained constant in a second group of 8 hearts during rate variation. The most pronounced inotropic effect was now found shortly after isolation of the heart. A rate increase of 30 beats/min resulted in a 20% rise of dP/dt max. The frequency potentiation decreased with deterioration of the heart resulting in a 12% dP/dt max increase at an estimated inotropic state of 50% of control. When the contractile state of the heart was improved above the control state by calcium application the frequency potentiation of the myocardium decreased. In the right ventricle similar results were obtained except for the fact that no significant correlation between the steepness of the frequency characteristics and the contractile state of the heart could be found when the end-diastolic pressure was kept constant.     

过氧化氢加重铁对心肌的损伤作用及其机制

采用Langendorff灌流心脏和酶解分离的心肌细胞为实验模型,研究铁对心肌的损伤作用,以及过氧化氢对铁的心肌作用的影响及其可能机制.结果显示(1)羟基喹啉铁复合物(Fe-HQ)引起分离心肌细胞舒张期缩短,心肌细胞的收缩幅度和速度降低,离体灌流心脏左室发展压(LVDP)、±dp/dtmax、心率、冠脉流量呈现双相变化;冠脉流出液中乳酸脱氢酶(LDH)、肌酸激酶(CK)释放量和心肌丙二醛(MDA)增高.(2)H2O2可加重Fe-HQ对心脏的损伤,冠脉流出液中LDH、CK释放量和心肌MDA增高,而LVDP、±dp/dtmax和心率明显降低.(3)还原型谷胱甘肽可对抗Fe-HQ+H2O2对心肌的损伤作用,DMSO对Fe-HQ+H2O2致离体心脏损伤无明显作用.结果提示,心肌细胞内铁增加可引起心肌功能受损,H2O2可加重铁对心肌的损伤作用,其主要机制可能与@OH无关,而主要与含巯基的蛋白质受损有关.     

Coronary effluent from a preconditioned heart activates the JAK-STAT pathway and induces cardioprotection in a donor heart

Preconditioning (PC) protects against ischemia-reperfusion (I/R) injury via the activation of the JAK-STAT pathway. We hypothesized that the mediators responsible for PC can be transferred to naive myocardium through the coronary effluent. Langendorff-perfused hearts from male Sprague-Dawley rats were randomized to paired donor/acceptor protocols with or without PC in the presence or absence of the JAK-2 inhibitor AG-490 (n = 6 for each group). Warmed, oxygenated coronary effluent collected during the reperfusion phases of PC (3 cycles of 5 min ischemia and 5 min reperfusion) was administered to acceptor hearts. The hearts were then subjected to 30 min ischemia and 40 min reperfusion. The left ventricles were analyzed for phosphorylated (p)STAT-1, pSTAT-3, Bax, Bcl, Bcl-X(L)/Bcl-2-associated protein (BAD), and caspase-3 expression by Western blot. A separate group of hearts (n = 6) was analyzed for STAT activation immediately after the transfer of the PC effluent (no I-R). Baseline cardiodynamics were not different among the groups. End-reperfusion maximal change in pressure over time (+dP/dt(max)) was significantly (P < 0.05) improved in acceptor PC (3,637 +/- 199 mmHg/s) and donor PC (4,304 +/- 347 mmHg/s) hearts over non-PC donor (2,020 +/- 363 mmHg/s) and acceptor (2,624 +/- 345 mmHg/s) hearts. Similar differences were seen for minimal change in pressure over time (-dP/dt(min)). STAT-3 activation was significantly increased in donor and acceptor PC hearts compared with non-PC hearts. Conversely, pSTAT-1 and Bax expression was decreased in donor and acceptor PC hearts compared with non-PC hearts. No differences in Bcl, BAD, or caspase-3 expression were observed. Treatment with AG-490 attenuated the recovery of +/-dP/dt in acceptor PC hearts and significantly reduced pSTAT-3 expression. The PC coronary effluent activates JAK-STAT signaling, limits apoptosis, and protects myocardial performance from I/R injury.     

Cardioprotective effects of stretch are mediated by activation of sarcolemmal, not mitochondrial, ATP-sensitive potassium channels

To determine whether sarcolemmal and/or mitochondrial ATP-sensitive potassium (K(ATP)) channels (sarcK(ATP), mitoK(ATP)) are involved in stretch-induced protection, isolated isovolumic rat hearts were assigned to the following protocols: nonstretched hearts were subjected to 20 min of global ischemia (Is) and 30 min of reperfusion, and before Is stretched hearts received 5 min of stretch + 10 min of no intervention. Stretch was induced by a transient increase in left ventricular end-diastolic pressure (LVEDP) from 10 to 40 mmHg. Other hearts received 5-hydroxydecanoate (5-HD; 100 microM), a selective inhibitor of mitoK(ATP), or HMR-1098 (20 microM), a selective inhibitor of sarcK(ATP), before the stretch protocol. Systolic function was assessed through left ventricular developed pressure (LVDP) and maximal rise in velocity of left ventricular pressure (+dP/dt(max)) and diastolic function through maximal decrease in velocity of left ventricular pressure (-dP/dt(max)) and LVEDP. Lactate dehydrogenase (LDH) release and ATP content were also measured. Stretch resulted in a significant increase of postischemic recovery and attenuation of diastolic stiffness. At 30 min of reperfusion LVDP and +dP/dt(max) were 87 +/- 4% and 92 +/- 6% and -dP/dt(max) and LVEDP were 95 +/- 9% and 10 +/- 4 mmHg vs. 57 +/- 6%, 53 +/- 6%, 57 +/- 10%, and 28 +/- 5 mmHg, respectively, in nonstretched hearts. Stretch increased ATP content and did not produce LDH release. 5-HD did not modify and HMR-1098 prevented the protection achieved by stretch. Our results show that the beneficial effects of stretch on postischemic myocardial dysfunction, cellular damage, and energetic state involve the participation of sarcK(ATP) but not mitoK(ATP).     

环加氧酶-2抑制剂尼美舒利通过改善内皮功能和增加NO含量对抗大鼠心肌氧化应激损伤

本文旨在研究冠状动脉内皮和NO在选择性环加氧酶2（cyclooxygenase2,COX-2）抑制剂尼美舒利（nimesulide）对抗心肌氧化损伤中的作用。离体大鼠心脏行Langendorff灌流,给予H2O2（140Bmol／L）观察心脏收缩功能。用U-46619灌流心脏,使冠状动脉预收缩后,观察冠状动脉对内皮依赖性舒张因子5-HT和内皮非依赖性舒张因子硝普钠（sodiumnitroprusside,SNP）的反应。结果显示：（1）与空白对照组（100％）相比,H202灌流20min后,左心室发展压[left ventriculardevelo pedpressure,LVDP,（54．8±4．0）％],和心室内压最大变化速率【±dp／dtmax（50．8±3．1）％和（46．2±2．9）％]明显降低。H2O2灌流前尼美舒利（5μmol/L）预处理10min,能够显著抑制H2O2引起的LVDP和μdp/dtmax下降[（79．9±2．8）％,（80．3±2．6）％和（81．4±2．6）％,P〈0．0l]。（2）与空白对照组相比,H2O2灌流后,5-HT和SNP引起内皮依赖性和内皮非依赖性血管舒张功能均明显下降;而尼美舒利预处理10min能明显对抗内皮依赖性血管舒张功能的下降[（-22．2±4．2）％vsH2O2组（-6．0±2．5）％,P〈0．0l],但对其内皮非依赖性血管舒张功能的下降没有明显作用[（-2．0±1．8）％vsH202组（-7．0±3．5）％,P〉0．05]。（3）一氧化氮合酶（nitric oxide synthase,NOS）抑制剂L-NAME能够部分取消尼美舒利预处理对H20,应激心脏心功能指标的改善作用ILVDP和±dp/dtmax分别为（60．2±2．1）％,（63．9±2．4）％和（63．1±2．9）％,P〈0．01]。同时尼美舒利预处理10min能使H202应激心肌NO含量增加[（2．63±0．40）vs（1．36±0．23）nmol／gprotein,P〈0．051,而L-NAME抑制此作用。（4）选择性COX-1抑制剂吡罗昔康（piroxicam）预处理不能抑制H202引起的LVDP和±dp/dtmax下降,但促进左心室舒张末压（1eftventricular end diastolicpressure,LVEDP）升高;吡罗昔康对H202引起的内皮依赖性和内皮非依赖性血管舒张功能下降无显著作用。以上结果提示,选择性COX-2抑制剂尼美舒利能够对抗大鼠离体心肌氧化应激损伤,其机制可能是通过改善内皮依赖性血管舒张功能和增加心肌NO含量起作用。     

Pharmacological evaluation of plasma membrane beta-adrenoceptors in rat hearts using the tissue segment binding method

This study evaluates beta-adrenoceptors in rat atria and ventricle using the tissue segment binding method and compares the results with those obtained using conventional homogenate binding assays. In studies with tissue segment binding, the hydrophilic radioligand [(3)H]-CGP12177 selectively bound to plasma membrane beta-adrenoceptors, and the B(max) levels were significantly higher than those obtained with homogenate binding. However, both binding approaches revealed similar proportions of beta(1)- and beta(2)-adrenoceptors. The regional distribution of plasma membrane beta(1)- and beta(2)-adrenoceptors in rat hearts were also determined using tissue segment binding. Abundance of beta-adrenoceptors and proportion of beta(1)-adrenoceptors were higher in atria than in ventricle, but there was no significant difference between right and left atria or within ventricle (right and left ventricle free walls, apex, and interventricular septum). To establish the ability of the tissue segment binding method to study beta-adrenoceptor regulation such as the internalization of receptors, the effect of prolonged exposure of rat ventricle to (-)-isoprenaline was also investigated by using tissue segments and homogenate binding. Incubation with (-)-isoprenaline for 1 h in vitro caused a concentration-dependent decrease in the density of beta-adrenoceptors, predominantly beta(2)-adrenoceptors, when assessed with tissue segment binding method. In contrast, the subtype-specific change after treatment with (-)-isoprenaline was not detected using homogenate binding. In summary, the tissue segment binding method with [(3)H]-CGP12177 enables a more precise quantitation of plasma membrane beta(1)- and beta(2)-adrenoceptors in rat hearts and is suitable for studying their regulation.     

Effect of eating bananas on plasma free and sulfate-conjugated catecholamines

The effect of eating bananas, a known and rich source of biogenic amines, on plasma free and sulfate-conjugated catecholamines was examined in normal human volunteers. Before ingestion conjugated norepinephrine (NE) and epinephrine (E) comprised 60% and 84% of the total concentration respectively. Free dopamine (DA) was undetectable. Although there was no change in free NE and E levels after eating bananas, free DA became measurable in some subjects. In contrast, conjugated NE and particularly DA, increased markedly in all subjects. More detailed study in 2 subjects indicated that this increase may persist for 8 hours after consumption. Available evidence suggests that sulfate conjugation of free catecholamines in banana largely takes place in the gut. It is important therefore to consider dietary influences when the physiological role of conjugated catecholamines. and perhaps free dopamine, is being assessed.