Studies on the mechanism of leukotriene induced coronary artery constriction

Leukotriene (LT) C₄, D₄,and E₄ at concentrations of 10 to 100 ng/ml were found to be potent coronary artery constrictors in the perfused cat coronary artery and perfused rat heart. In contrast, LTB₄, was essentially inactive. The coronary constrictor effect of leukotrienes was not related to thromboxane release, but rather appeared to be due to a calcium mediated activation of specific leukotriene receptors.     

Effects of intra-coronary administration of leukotriene D4 in the anaesthetized dog

The left anterior descending coronary artery in anaesthetized greyhounds was perfused at constant pressure with blood pumped from the carotid artery. Phasic and mean coronary flow, left ventricular pressure, dP/dt, cardiac output, ECG, heart rate and systemic pressure were measured. Leukotriene (LT) D₄ was administered into the left anterior descending coronary artery as a bolus injection. LTD₄ caused dose-related reductions in coronary flow. Other parameters showed little immediate change although a gradual decrease in left ventricular pressure, dP/dt, cardiac output and systemic pressure occurred after administration of LTD₄. Following intracoronary administration of LTD₄ small surface haemorrhages were observed over the area perfused. The reduction in coronary flow was not inhibited by indomethacin.     

Synthesis and vascular actions of an arachidonic acid ethylene-diamino-triethyl-ester (AA-EDTA) derivative

An ethylene-diamino-triethyl-ester derivative of arachidonic acid (AA-EDTA) was newly synthesized and tested for its coronary vasoactivity in isolated perfused cat coronary arteries. This arachidonic acid analog exerted a coronary vasodilator effect and significantly antagonized the coronary vasoconstrictor effect of LTD4. The constrictor response to the thromboxane analog carbocyclic thromboxane A2 was unaffected by AA-EDTA. These properties of AA-EDTA may be useful in counteracting the vasoconstrictor influence of leukotrienes in situations such as coronary artery vasospasm.     

Synthesis and vascular actions of an arachidonic acid ethylene-diamino-triethyl-ester (AA-EDTA) derivative

An ethylene-diamino-triethyl-ester derivative of arachidonic acid (AA-EDTA) was newly synthetized and tested for its coronary vasoactivity in isolated perfused cat coronary arteries. This arachidonic acid analog exerted a coronary vasodilator effect and significantly antagonized the coronary vasoconstrictor effect of LTD₄. The constrictor response to the thromboxane analog carbocyclic thromboxane A₂ was unaffected by AA-EDTA. These properties of AA-EDTA may be useful in counteracting the vasoconstrictor influence of leukotrienes in situations such as coronary artery vasospasm.     

Dependence of nickel-induced coronary vasoconstriction on the activity of the electrogenic Na+, K+-pump

The possible interactions between the vasoactive trace metal nickel ion (Ni2+) and membrane Na-K-ATPase in the isolated perfused rat heart and in the isolated canine coronary artery have been studied. The characteristic features of 1 microM Ni2+-induced contractile response in the canine coronary artery strip were similar to those evoked by the inhibition of Na-K-ATPase. Inhibition of the pump activity by ouabain (10(-4)M) or by K+-deficient Krebs solution prevented Ni2+-action both in the canine coronary artery strip and in the perfused rat heart, indicating that when Ni2+ causes coronary vasoconstriction the Na, K-exchange is influenced. Further studies are needed to clarify whether Ni2+ acts directly on the enzyme, or the vascular action of this trace metal depends on the ionic gradients maintained by the electrogenic Na-K-pump.     

Scaling of myocardial mass to flow and morphometry of coronary arteries.

There is no doubt that scaling relations exist between myocardial mass and morphometry of coronary vasculature. The purpose of this study is to quantify several morphological (diameter, length, and volume) and functional (flow) parameters of the coronary arterial tree in relation to myocardial mass. Eight normal porcine hearts of 117-244 g (mean of 177.5 +/- 32.7) were used in this study. Various coronary subtrees of the left anterior descending, right coronary, and left circumflex arteries were perfused at pressure of 100 mmHg with different colors of a polymer (Microfil) to obtain rubber casts of arterial trees corresponding to different regions of myocardial mass. Volume, diameter, and cumulative length of coronary arteries were reconstructed from casts to analyze their relationship to the perfused myocardial mass. Volumetric flow was measured in relationship with perfused myocardial mass. Our results show that arterial volume is linearly related to regional myocardial mass, whereas the sum of coronary arterial branch lengths, vessel diameters, and volumetric flow show an approximately 3/4, 3/8, and 3/4 power-law relationship, respectively, in relation to myocardial mass. These scaling laws suggest fundamental design principles underlying the structure-function relationship of the coronary arterial tree that may facilitate diagnosis and management of diffuse coronary artery disease.     

The effects of periarterial nerve activation on coronary vessel tone in an isolated and perfused slab of beef ventricle.

The direct effects of extrinsic nerve stimulation on coronary artery tone are unclear because of the complications arising from alterations in myocardial dynamics which themselves alter flow. An isolated and perfused nonbeating slab of beef ventricle was utilized in the present experiments to eliminate secondary complications and the efects of periarterial nerve activation on coronary perfusion pressure were examined. It was found that stimulation induced vasoconstrictor responses which were enhanced by physostigmine, a cholinesterase inhibitor, and blocked by atropine. These responses were duplicated by exogenous acetylcholine both in the perfused preparation and in isolated strips of coronary artery. Although added noradrenaline gave vasodilatation, no response attributable to the release of noradrenaline from nerves was obtained. It is concluded that the coronary vasculature of the beef receives a cholinergic innervation and that its activation, especially under conditions of reduced transmitter degradation, may induce considerable coronary vessel constriction.     

Diameter-dependent axial prestretch of porcine coronary arteries and veins

The pressure-diameter relation (PDR) and the wall strain of coronary blood vessels have important implications for coronary blood flow and arthrosclerosis, respectively. Previous studies have shown that these mechanical quantities are significantly affected by the axial stretch of the vessels. The objective of this study was to measure the physiological axial stretch in the coronary vasculature; i.e., from left anterior descending (LAD) artery tree to coronary sinus vein and to determine its effect on the PDR and hence wall stiffness. Silicone elastomer was perfused through the LAD artery and coronary sinus trees to cast the vessels at the physiologic pressure. The results show that the physiological axial stretch exists for orders 4 to 11 (> 24 μm in diameter) arteries and orders -4 to -12 (>38 μm in diameter) veins but vanishes for the smaller vessels. Statistically, the axial stretch is higher for larger vessels and is higher for arteries than veins. The axial stretch λ(z) shows a linear variation with the order number (n) as: λ(z) = 0.062n + 0.75 (R(2) = 0.99) for artery and λ(z) = -0.029n + 0.89 (R(2) = 0.99) for vein. The mechanical analysis shows that the axial stretch significantly affects the PDR of the larger vessels. The circumferential stretch/strain was found to be significantly higher for the epicardial arteries (orders 9-11), which are free of myocardium constraint, than the intramyocardial arteries (orders 4-8). These findings have fundamental implications for coronary blood vessel mechanics.     

Changes in the myocardial ultrastructure of the perfused rabbit heart under hypoxia

Ultrastructure of rabbit heart left ventricle isolated according to Langendorf was examined under different conditions: in intact animals, during ligation of the coronary artery, and hypoxic heart perfusion. The intact perfused heart showed unmarked exo- and intracellular edema and moderate swelling of the mitochondria. During hypoxic perfusion, marked swelling and destruction of the mitochondria were noted. During ligation of the coronary artery, the heart was characterized by a high degree of mitochondrial heterogenicity. The correlation of the data obtained allowed one to reveal the myocardial adaptive-accommodative mechanism, (intermittent mitochondrial activity) that makes it possible to maintain the heart bioenergetics during coronary artery occlusion at a permanently high level.     

Relationship between arterial diameter and perfused tissue volume in myocardial microcirculation: a micro-CT-based analysis

The volume of myocardial tissue that is perfused by an epicardial coronary artery has been shown to be predictably related to the diameter of the epicardial arterial lumen. However, to what extent the intramyocardial microvasculature follows the epicardial rules remains unclear. To explore the relationship between the diameter of coronary arterioles and their subsequent perfused myocardial volumes, we quantified the volume of nonperfused myocardium resulting from an embolized arteriole of a certain diameter. We injected a single dose of microspheres selected from one of nine possible microsphere combinations (10, 30, and 100 microm diameter, each at three possible doses) into the left anterior descending coronary and/or left circumflex arteries of seven anesthetized pigs. At postmortem, the coronary arteries were infused with a radiopaque silicon polymer. Embolized myocardium (1 cm(3)) was scanned with a microcomputerized tomography scanner and resulted in three-dimensional images that consisted of 20 microm/side cubic voxels and a subvolume of the specimen with 4 microm/side cubic voxels. Image analysis provided the number and volumes of myocardial perfusion defects for each size and dose of microspheres. The smallest individual myocardial perfusion defects, which correspond to the volume of myocardium perfused by a single embolized arteriole, were found to be 0.0004 +/- 0.0002, 0.02 +/- 0.004, and 0.62 +/- 0.099 mm(3) for the 10-, 30-, and 100-microm microspheres, respectively. The number of myocardial perfusion defects in the embolized myocardium was inversely related to the dose of the injected microspheres. This reflects a clustering behavior that is consistent with a random distribution process of the individual embolized perfusion defects.     

Heat transfer mediated by coronary circulation in Langendorff-perfused isolated whole hearts

Although coronary flow is essential for oxygen supply, which is a prerequisite for cardiac electrical activity, energy metabolism and mechanical performance, the roles of coronary circulation on heat transfer to the heart have received less attention. This study investigated the effects of coronary circulation on epicardial temperature, the effects of temperature on coronary resistance, and the effects of ischemia on temperature fall, using isolated perfused rat or guinea pig hearts. Monophasic action potential (MAP) and epicardial temperature were recorded by a pair of suction electrodes and thermisters, while whole heart conductance (WHC) was estimated by a two-electrode instrument arranged in a diagonal array, under the alteration of the coronary flow rate of perfusate with different temperatures. MAP duration was sensitive to the local temperature, and lowering the temperature caused reduced WHC and increased coronary resistance calculated by dividing perfusion pressure by flow rate. After the onset of ischemia, WHC fell immediately in a single exponential manner, and MAP duration was abbreviated after transient behaviors explained well by the exquisite temperature gradient governed by coronary artery geometry. Epicardial temperature is maintained by coronary circulation in isolated perfused heart. Temperature-sensitive coronary tonus and MAP duration indicate that an exquisite temperature gradient underlies inhomogeneous distributions of coronary flow and electrical property. No-flow ischemia disturbs heat transfer and augments the temperature gradient transiently. Therefore, an isolated perfused heart can be considered as a heat transfer model where thermoregulation is maintained by warm coronary perfusion.     

Coronary flow measurements on the isolated rat heart following experimental coronary artery stenosis]

A stenosing proliferation of the vascular wall was produced by exposing the Ramus descendens of the rat's left coronary artery to continued mechanical stimulation. Two weeks after the operation the hearts were perfused according to a modified Langendorff method, and the flow rate was measured under aerobic conditions and following short-time anoxia. Under either experimental conditions, the flow rate proved to be significantly decreased.     

Clinical evidence for myocardial derecruitment downstream from severe stenosis: pressure-flow control interaction

To verify the interaction between coronary pressure (CP) and blood flow (CBF) control, we studied nine candidates for angioplasty of an isolated lesion of the left anterior descending coronary artery [i.e. , percutaneous transluminal coronary angioplasty (PTCA)]. CBF (i.e., flow velocity x coronary cross-sectional area at the Doppler tip) and CP were monitored during washout of 2-5 mCi of (133)Xe after bolus injection into the left main artery before and after PTCA. Xe mean transit time (MTT) was calculated as the area under the time-activity curve, acquired by a gamma camera, divided by the dose obtained from a model fit of the Xe curve in the anterior wall. CBF response to intracoronary adenosine (2 mg) was also assessed. PTCA increased baseline CBF (from 14.5 +/- 9.4 to 20 +/- 8 ml/min, P < 0.01), coronary flow reserve (from 1.52 +/- 0.24 to 2.33 +/- 0.8, P < 0.01), and CP (from 64 +/- 9 to 100 +/- 10 mmHg, P < 0.05). MTT decreased from 89 +/- 32 to 70 +/- 19 s (P < 0.05) after PTCA; however, MTT and CBF changes were not correlated (r = -0.09, not significant). Inasmuch as MTT is the ratio of distribution volume to CBF, MTT x CBF was used as an index of perfused myocardial volume. Volume increased after PTCA from 23 +/- 18 to 56 +/- 30 ml. A direct correlation was observed between the percent increase in distal CP and percent increase in perfused volume (r = 0.91, P < 0.01). Thus low CP was not associated with exhaustion of flow reserve but, rather, with reduction of perfused myocardial volume. These data suggest that, in the presence of a severe coronary stenosis, derecruitment of vascular units occurs that is proportional to the decrease in driving pressure. Residual perfused units maintain a vasomotor tone, thus explaining the paradoxical persistence of coronary reserve.     

The role of adrenergic receptors in Ni2+-induced coronary vasoconstriction

The possible involvement of adrenergic receptors in nickel ion (Ni2+)-induced coronary vasoconstriction was studied on isolated perfused rat hearts and on isolated canine coronary artery strips. The experiments on both models showed that (i) alfa-adrenergic blockade by phenoxybenzamine or phentholamine caused only partial depression of Ni2+-induced coronary vasoconstriction: (ii) beta-adrenergic receptor blockade by propranolol totally prevented Ni2+-action, and (iii) Ni2+ (1 microM) caused significant inhibition of coronary vasodilatation induced by isoproterenol. The experimental results indicate that alfa-adrenoceptors play minor role (if any) in the coronary action mechanism of Ni2+ but it may be mediated by beta-adrenergic mechanisms. Nickel was found to alter the reactivity of coronary beta-adrenoceptors suggesting a possible modulatory role of this trace metal in coronary adrenergic mechanisms.     

Inhibitory effects of L-NG-nitro-arginine on the synthesis of EDRF and the cerebroarterial response to vasodilator nerve stimulation

Treatment with L-NG-nitro-arginine (L-NA) inhibited the brady-kinin-induced relaxation, mediated via EDRF, in dog coronary artery strips partially contracted with prostaglandin F2 alpha; the inhibition was prevented by L-, but not D-, arginine. Relaxation caused by nitroglycerin was not altered by L-NA. The release of EDRF, as assayed using dog coronary artery strips without endothelium, from perfused femoral artery segments with endothelium in response to acetylcholine and substance P was significantly reduced by treatment of the femoral artery with L-NA. The inhibitory effect was reversed by L-arginine. Relaxant responses of dog cerebral artery strips with and without endothelium to electrical stimulation of non-adrenergic, non-cholinergic nerves were suppressed by L-NA, whereas relaxation of coronary arteries with and without endothelium by the stimulation of adrenergic nerves was not influenced. The L-NA-induced inhibition was reversed by L-arginine. It is speculated that L-NA inhibits the synthesis of EDRF, as does L-NG-monomethyl arginine, and NO-like substance(s) produced plays an important role in transferring information from vasodilator nerves to smooth muscle in cerebral arteries.     

Redistribution in left ventricular regional flow following acute right ventricular pressure overload

The left ventricular dysfunction following acute pulmowary hypertension remains unexplained. We wondered if acute pulmonary hypertension could alter the transmural flow distribution within the left ventricular myocardium, independent of coronary flow and perfusion pressure. We used a canine preparation in which the left coronary system was perfused at constant flow and induced a two- to three-fold increase in pulmonary artery pressure by banding the pulmonary artery. Regional myocardial blood flow of the left coronary system was measured using radioactive microspheres, injected into the left coronary system before and after 10-30 min of banding of the pulmonary artery. The left ventricular subendocardial:epicardial ratio fell by 12 and 31% (p less than 0.05) of control value, 10 and 30 min, respectively, after banding of the pulmonary artery, the total flow to the left coronary system being kept constant. Left atrial mean pressure increased from 2.9 +/- 2.4 to 3.6 +/- 1.9 and 6.0 +/- 2.1 (p less than 0.05) following banding. The mechanism of the redistribution of coronary flow may relate to inappropriate vasodilation of the right septal myocardium with consequent relative left ventricular subendocardial hypoperfusion which might aggravate left ventricular ischemia in the presence of hypotension and hypoxia.     

Apelin reduces myocardial reperfusion injury independently of PI3K/Akt and P70S6 kinase

Apelin, the endogenous ligand of the G protein-coupled APJ receptor, is a peptide mediator with emerging regulatory actions in the heart. The aim of the present studies was to explore potential roles of the apelin/APJ system in myocardial ischaemia/reperfusion injury. To determine the cardiac expression of apelin/APJ and potential regulation by acute ischaemic insult, Langendorff perfused rat hearts were subjected to regional ischaemia (left coronary artery occlusion, 35 min) or ischaemia followed by reperfusion (30 min). Apelin and APJ mRNA expression were then determined in ventricular myocardium by rt-PCR. Unlike APJ mRNA expression, which remained unchanged, apelin mRNA was upregulated 2.4 fold in ventricular myocardium from isolated rat hearts undergoing ischaemia alone, but returned back to control levels after 30 min reperfusion. We then proceeded to test the hypothesis that treatment with exogenous apelin is protective against ischaemia/reperfusion injury. Perfused hearts were subjected to 35 min left main coronary artery occlusion and 120 min reperfusion, after which infarct size was determined by tetrazolium staining. Exogenous Pyr(1)-apelin-13 (10(-8 )M) was perfused either from 5 min prior to 15 min after coronary occlusion, or from 5 min prior to 15 min after reperfusion. Whilst ineffective when used during ischaemia alone, apelin administered during reperfusion significantly reduced infarct size (47.6+/-2.6% of ischaemic risk zone compared to 62.6+/-2.8% in control, n=10 each, p<0.05) in hearts subject to temporary coronary occlusion followed by reperfusion. This protective effect was not abolished by co-administration of the PI3K inhibitor wortmannin (10(-7 )M, infarct size 49.8+/-4.1%, n=4) or the P70S6 kinase inhibitor rapamycin (10(-9 )M, 41.8+/-8.8%, n=4). In conclusion these results suggest that apelin may be a new and potentially important cardioprotective autacoid, upregulated rapidly after myocardial ischaemia and acting through an unknown pathway.     

正常小鼠冠状动脉的超声成像技术分析

目的探讨利用高频小动物心脏超声对C57BL／6小鼠冠状动脉进行评价的可行性,为小鼠冠状动脉相关疾病动物模型的制备及其功能评价提供依据。方法采用Vevo770型高分辨小动物超声仪,频率30mHz的宽频探头,对20只健康C57BL／6小鼠于4、8和12周龄时冠状动脉的情况进行观察。测定和分析不同周龄小鼠冠状动脉内径值的变化。结果全部20只小鼠超声均成功检测到冠状动脉。超声心动图显示小鼠4周龄时左冠状动脉主干内径检测值为0．36±0．02mm,右冠状动脉主干内径值为0．29±0．03mm;8周龄时左冠状动脉主干内径值为0．38±0．06mm,右冠状动脉主干内径值为0．37±0．02（mm）;12周龄时左冠状动脉主干内径值为0．38±0．02mm,右冠状动脉主干内径值为0．39±0．03mm。结论利用高频小动物心脏超声可获取正常小鼠清晰的冠状动脉图像,并能准确反映小鼠冠状动脉内径值动态变化。为小鼠冠状动脉疾病模型的制备及其功能评价提供依据。     

犬冠状动脉阻力的胆碱能调节

本实验在麻醉开胸犬,采用冠状动脉左旋支恒流灌注,于搏动的和心室纤颤(VF)的心脏,研究了电刺激迷走神经(VNS)及冠状动脉内注入乙酰胆碱(ACh)对冠状动脉阻力的影响。当 VNS 和冠脉内给 ACh 时,(1)心肌内小冠状动脉阻力显著减低,而心外膜大冠状动脉阻力并无明显变化;(2)冠状动脉左旋支总阻力的减低幅度在 VF 的心脏比在搏动的心脏显著减小。以上结果表明,迷走-ACh 扩张冠脉的作用主要是舒张心肌内小冠状动脉,并可通过减低心肌收缩力而间接降低冠状动脉阻力。