Flow- and acetylcholine-induced dilatation in small arteries from rats with renovascular hypertension--effect of tempol treatment

We investigated whether renovascular hypertension alters vasodilatation mediated by nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) and the influence of the superoxide dismutase mimetic tempol on vasodilatation. One-kidney one-clip hypertensive Sprague-Dawley rats, treated with either vehicle or tempol (from weeks 5 to 10 after placement of the clip), and uninephrectomized control rats were investigated. In renal hypertensive rats systolic blood pressure increased to 171+/-6 mmHg (n=10), while in tempol-treated rats systolic blood pressure remained normal (139+/-7 mmHg, n=5). In isolated pressurized mesenteric small arteries NO-mediated dilatation was obtained by increasing flow rate and EDHF-mediated dilatation by acetylcholine. In arteries from hypertensive rats, flow-induced dilatation was blunted, as compared to normotensive and tempol-treated rats, while acetylcholine-induced dilatation remained normal. Measured by dihydroethidium staining there was an increased amount of superoxide in arteries from vehicle-treated rats, but not from tempol-treated rats. Expression by immunoblotting of endothelial NO synthase and the NAD(P)H oxidase subunit p47phox remained unaffected by high blood pressure and tempol treatment. Simultaneous measurements of NO-concentration and relaxation were performed in isolated coronary arteries from the same animals. As compared to vehicle-treated rats, both acetylcholine-induced relaxation and NO-concentration increased in arteries from tempol-treated animals, while only the relaxation was improved by the NO donor, S-nitroso-N-acetylpenicillamine (SNAP). In conclusion renovascular hypertension selectively inhibits flow-induced NO-mediated vasodilatation, while EDHF-type vasodilatation remains unaffected, suggesting that high blood pressure leads to increased generation of superoxide contributing to decreased NO bioavailability. Furthermore, the abnormal endothelium function can be corrected by tempol treatment, but this seems to involve mechanisms partly independent of NO.     

Elevated pressure selectively blunts flow-evoked vasodilatation in rat mesenteric small arteries

BACKGROUND AND PURPOSE: The present study investigated mechanisms underlying impaired endothelium-dependent vasodilatation elicited by elevating the intraluminal pressure in rat mesenteric small arteries. EXPERIMENTAL APPROACH: Arterial segments (internal diameter 316+/-2 microm, n=86) were mounted in a pressure myograph. The effect of elevating pressure from 50 to 120 mmHg for 1 h before resetting it to 50 mmHg was studied on endothelium-dependent vasodilatation. KEY RESULTS: In arteries constricted with U46619 in the presence of indomethacin, shear stress generated by flow, evoked vasodilatation that was abolished by an inhibitor of nitric oxide (NO) synthase, asymmetric dimethylarginine (1 mM), whereas acetylcholine-induced vasodilatation was unchanged. After elevation of intraluminal pressure for 1 h and then resetting it to 50 mmHg, vasodilatation induced by shear stress and the NO donor, S-nitrosopenicillamine was inhibited, while vasodilatation induced by a guanylyl cyclase activator, BAY 412272, and acetylcholine was unaltered. Superoxide levels sensitive to polyethylene glycol superoxide dismutase were increased in segments exposed to elevated pressure. A superoxide scavenger, tempol (300 microM), a general endothelin receptor antagonist, SB 217242 and the selective ET(A) receptor antagonist, BQ 123 preserved shear stress-evoked vasodilatation. CONCLUSIONS AND IMPLICATIONS: The present study shows that transient exposure to an elevated intraluminal pressure selectively inhibits flow-evoked NO-mediated vasodilatation, probably through activation of endothelin receptors and increased formation of superoxide. In contrast, elevation of pressure did not affect the acetylcholine-evoked endothelium-derived hyperpolarizing factor type vasodilatation in mesenteric small arteries.     

Ischaemia/reperfusion selectively attenuates coronary vasodilatation to an adenosine A2- but not to an A1-agonist in the dog.

1. The effects of myocardial ischaemia/reperfusion were tested on the coronary vasorelaxant responses to agonists selective for the A1 and A2 adenosine receptor subtypes in the dog. The left anterior descending (LAD) coronary artery was occluded distal to the first diagonal branch. The occlusion was maintained for 1 h, followed by 1 h of reperfusion. 2. In the first series of experiments, LAD and circumflex arteries were excised and contracted with prostaglandin F2 alpha (PGF2 alpha). Ischaemia/reperfusion did not significantly alter the vasorelaxation produced by either sodium nitroprusside (endothelium-independent) or acetylcholine (endothelium-dependent). The A1 selective agonist, cyclopentyladenosine (CPA), produced coronary vasorelaxation in both normally perfused vessels and vessels subjected to ischaemia/reperfusion. In contrast, the relaxation produced by the A2-selective agonist N6-[2-(3,5-dimethoxyphenyl)-2-(2-methylphenyl) ethyl] adenosine (DPMA) was significantly attenuated by ischaemia/reperfusion (14 fold shift in EC50). 3. In the second series of experiments, coronary blood flow was increased by administration of the A1 and A2 agonists before and after ischaemia/reperfusion of the LAD in anaesthetized dogs. Both compounds dose-dependently increased coronary blood flow. The slopes of the dose-response functions to CPA or DPMA were not significantly altered in the normally perfused circumflex vascular bed. Similarly, the CPA dose-response function in the LAD was unaltered by ischaemia/reperfusion. However, the slope of the coronary vasodilator response to the A2 agonist was significantly reduced following ischaemia/reperfusion of the LAD. 4. We conclude that ischaemia/reperfusion reduces responsiveness to an adenosine A2 receptor subtype agonist, but not an A1 receptor subtype agonist. These data confirm the independent nature of A1- and A2-mediated coronary vasodilatation.     

Haemodynamic factors influencing myocardial ischaemia in a canine model of coronary artery stenosis: the effects of nitroglycerine.

At a critical degree of coronary stenosis (allowing a just adequate blood supply to the poststenotic area only at the expense of maximal hypoxic coronary vasodilatation), an additional loading of the heart induced marked local myocardial ischaemia, as indicated by appropriate biochemical, electrophysiological and haemodynamic changes. In this model myocardial oxygen demand was increased in three different ways: (i) increasing heart rate by atrial pacing; (ii) increasing afterload by aortic occlusion and (iii) increasing preload by blood infusion. These procedures were compared in their ability to produce local myocardial ischaemia and characterized by ST-segment elevation recorded from the endocardium and epicardium. Increasing afterload evoked the mildest degree of ischaemia since the resulting increase in coronary perfusion pressure and coronary flow almost met the augmented myocardial oxygen demand evoked by the elevated peripheral resistance and by the simultaneously increased preload. A rather more pronounced ischaemia was produced by increasing the preload. The most serious ischaemia of all was induced by atrial pacing. This reduced coronary flow and perfusion pressure and increased left ventricular end diastolic pressure (LVEDP). Nitroglycerine transiently reduced blood pressure and coronary blood flow and increased epicardial and endocardial ST-segment elevation; the changes had disappeared 10 min after terminating the infusion. However, at this time a prolonged protective action against pacing-induced ST-segment elevation was observed. This protection was also seen after intracoronary injections of nitroglycerine. This indicated that part of the beneficial effect of nitroglycerine in ischaemia is due to direct coronary and/or myocardial actions.     

Cytochrome p450 2C inhibition reduces post-ischemic vascular dysfunction

Cytochrome p450 (CYP) inhibitors provide protection against myocardial infarction following both global and focal cardiac ischemia and reperfusion (I/R). We hypothesized that sulfaphenazole, an inhibitor of CYP2C6 and 9, also attenuates post-ischemic endothelial dysfunction by reducing CYP-mediated superoxide generation (which scavenges nitric oxide (NO)), thereby restoring NO bioavailability and vascular tone. Rat hearts were perfused in the Langendorff mode for 20 min in the presence, or absence, of sulfaphenazole and then subjected to 30 min global no-flow ischemia followed by 15 min reperfusion. Septal coronary resistance arteries were isolated and mounted on glass cannulae for measurements of luminal diameter. Preconstricted arteries were exposed to acetylcholine to elicit endothelium-dependent, NO-mediated vasodilation. Acetylcholine caused near maximal dilation in control tissues not subjected to I/R. Following I/R, endothelium-dependent vasodilation was reduced. Pretreatment with sulfaphenazole restored endothelial sensitivity to acetylcholine. Vasoresponsiveness to endothelium-independent vasodilators, sodium nitroprusside and isoproterenol, were also reduced following I/R. However, sensitivity to endothelium-independent vasodilators was not restored by pretreatment with sulfaphenazole. I/R-induced superoxide production was assessed by dihydroethidium staining of flash frozen hearts. Sulfaphenazole treatment significantly reduced superoxide production in arterial walls following I/R injury. We conclude that sulfaphenazole restores post-ischemic endothelium-dependent, NO-mediated vasodilation by reducing superoxide production, suggesting that CYP2C9 plays a key role in post-ischemic vascular dysfunction.     

大鼠心肌梗死后非梗死区基质重构及相关调节因子变化的研究

目的:探讨大鼠急性心肌梗死后非梗死区心肌基质重构的机制及相关调节因子的变化。方法:结扎左冠状动脉前降支制作大鼠心肌梗死模型,分别于造模后1、3、7、14和28d处死动物,采用Masson染色检测非梗死区心肌胶原容积分数(CVF),明胶酶谱法检测基质金属蛋白酶(MMP)-2、金属蛋白酶组织抑制剂(TIMP)-2的活性,实时荧光定量PCR法检测核转录因子(NF)-κBmRNA、肿瘤坏死因子(TNF)-αmRNA表达。结果:与假手术组相比较,心肌梗死组大鼠非梗死区CVF随梗死后时间的延长而增加,28d最明显(P<0.01);MMP-2、TIMP-2活性随时间延长而增加,二者在梗死后14d达高峰,后有所下降,28d时活性仍高于假手术组(P<0.05);TNF-α的表达于梗死后7d达高峰(P<0.01),后有所下降,持续到28d仍高于假手术组(P<0.05);NF-κB的表达活性随梗死时间的延长而增加(P<0.05或P<0.01)。结论:急性心肌梗死后心肌非梗死区MMP-2/TIMP-2及相关调节因子活性改变具有明显时间依从性,是导致非梗死区基质重构的机制之一。     

The effect of ischaemia on endothelium-dependent vasodilatation and adrenoceptor-mediated vasoconstriction in rat isolated hearts.

1. The aim of this study was to investigate whether global ischaemia and reperfusion in rat isolated hearts affects endothelium-dependent vasodilatation and adrenoceptor-mediated vasoconstriction. In addition, it was first determined whether inhibition of the actions of nitric oxide (NO) influenced the responses to alpha-adrenoceptor agonists in the rat coronary vasculature. 2. In rat isolated, Langendorff perfused hearts, inhibition of NO with haemoglobin (Hb, 6 microM) significantly inhibited the vasodilator responses to the endothelium-dependent vasodilators, acetylcholine (ACh, 3-100 pmol), carbachol (CCh, 10-300 pmol), bradykinin (Bk, 1-30 pmol) and histamine (0.3-10 nmol) but did not affect responses to the endothelium-independent vasodilator, sodium nitroprusside (SNP, 0.01-1 nmol). 3. Inhibition of the action of NO by Hb significantly enhanced the vasoconstrictor response to the non-selective alpha-adrenoceptor agonist, noradrenaline (NA, 0.1-10 nmol) and the alpha 2-adrenoceptor agonist, B-HT 920 (0.001-1 mumol) but had no effect on the vascular response to the alpha 1-adrenoceptor agonist, methoxamine (MTX, 10-300 nmol). 4. In the perfused hearts ischaemia, induced by 30 min perfusion at 5% of the normal rate of flow, followed by 15 min of reperfusion (ischaemia/reperfusion) selectively impaired the vasodilator responses to ACh and CCh which act by muscarinic receptor stimulation but did not affect responses to the other endothelium-dependent vasodilators Bk and histamine or to the endothelium-independent dilator SNP. 5. After ischaemia/reperfusion the coronary vasoconstrictor responses to B-HT 920 were slightly but significantly enhanced whereas the responses to NA and MTX were unaffected. 6. Thus, in the rat isolated heart, low flow induced-ischaemia and reperfusion causes a selective impairment of muscarinic receptor-mediated vasodilatation but does not impair responses to all endothelium-dependent vasodilators. Enhanced constrictor responses to noradrenaline and B-HT 920 in the presence of Hb indicates that endogenous NO modulates the constriction of coronary resistance vessels in response to stimulation of alpha 2-adrenoceptors. Ischaemia and reperfusion in this isolated vascular bed caused only a small increase in the coronary vasoconstrictor response to alpha 2-adrenoceptor stimulation. It appears that in the rat isolated heart the degree of endothelial dysfunction caused by ischaemia/reperfusion is insufficient to cause a functionally significant change in alpha-adrenoceptor-mediated constriction.     

Impaired heart function and noradrenaline release after ischaemia in stroke-prone spontaneously hypertensive rats

1. Stroke-prone spontaneously hypertensive rats (SHRSP) are a strain of rat that exhibit severely high blood pressure and stroke attacks at an early age, but their heart function in vitro has seldom been studied in detail. Although the activity of the sympathetic nervous system is known to increase after myocardial ischaemia, there is little information about the cardiac release of noradrenaline (NA) associated with heart function after ischaemia in SHRSP. The aim of the present study was to examine heart function and cardiac NA release after ischaemia in SHRSP. 2. Isolated hearts of 4- and 8-month-old SHRSP and age-matched Wistar-Kyoto (WKY) rats were perfused in a working heart preparation and were subjected to 30 min ischaemia followed by 30 min reperfusion. Heart function and coronary flow were monitored throughout the experiment. Coronary effluent was collected for determination of NA using high-performance liquid chromatography coupled with electrochemical detection. 3. Under baseline conditions, cardiac output of 4-month-old SHRSP was slightly but significantly decreased compared with that of WKY rats (P < 0.05), although coronary flow was maintained normally at this age. Eight-month-old SHRSP showed a further impairment of systolic heart function, with lower coronary flow and higher coronary vascular resistance under baseline conditions. Elevated left ventricular end-diastolic pressure was evident in SHRSP at both ages before ischaemia. Heart function was severely damaged after 30 min global ischaemia in SHRSP from both age groups. Stroke-prone spontaneously hypertensive rats also showed lower coronary flow and higher coronary vascular resistance during reperfusion. 4. Coronary NA was not detectable in WKY rats or SHRSP at 4 months of age under baseline conditions. In 8-month-old SHRSP, pre-ischaemic NA release was significantly higher than that in age-matched WKY rat controls. The concentration of NA in the coronary effluent of SHRSP during reperfusion was also significantly higher than that of WKY rats at both ages. 5. These data demonstrate that SHRSP have early impairment of both systolic and diastolic heart function compared with WKY rats. Severe damage of heart function and coronary flow after ischaemia in SHRSP was accompanied with an increased release of NA, which may play a harmful role in heart function impairment in SHRSP after ischaemia.     

Time-dependent expression pattern of nitric oxide and superoxide after myocardial infarction in rats.

Previous experiments by our group have demonstrated a subacute increased contribution of nitric oxide (NO) to vasoreactivity after myocardial infarction in rats. However, the activation pattern of NO may be phasic after infarction and has been described to be strongly associated with superoxide production. Therefore, the present study evaluated the morphological distribution and time-dependent induction of NO and superoxide at the protein (via immunohistochemistry, chemiluminescence and spectrophotometry) and mRNA (via real-time RT-PCR) level after experimental induction of a myocardial infarction in rats. Myocardial infarction led to a modest but lasting upregulation of endothelial NO synthase (eNOS) in blood vessels and cardiomyocytes. In contrast, inducible NOS (iNOS) showed dramatic de novo formation 1 week after infarction, predominantly in the infarcted area and cardiomyocytes. In addition, a gradually increased myocardial production of superoxide was detected during remodelling, probably related by an upregulation of NADH oxidase in the peri-infarcted and remote myocardium. Furthermore, peroxynitrite formation was increased after myocardial infarction, indicating strong interaction between NO and superoxide. In conclusion, during the early remodelling phase after myocardial infarction mRNA concentrations and protein levels of eNOS and iNOS show an augmentation in a biphasic manner. Moreover, upregulation of NADH oxidase leads to increased presence of superoxide and peroxynitrite and thereby to a reduction of the bioavailability and compensatory effects of NO, as such influencing post-infarction remodelling.     

Coronary vasodilatation and adrenergic receptors in the dog heart and coronary.

The question of whether the coronary blood vessels contain an intrinsic adrenergic mechanism for vasodilatation of physiological significance has been examined in the canine heart-lung preparation with a donor by studying the response of the coronary vessels to epinephrine, norepinephrine, isoproterenol and salbutamol in combination with practolol. To differentiate the vasodilatation mediated through adrenoceptors in the coronary vessels from that resulting from an increase in the myocardial O2 consumption, a special method of analysis was developed based on the linear relation between the coronary flow and the myocardial O2 consumption. It was found that all four compounds produced an increase in the coronary flow attributable to an increased myocardial O2 consumption. Epinephrine and norepinephrine produced a decrease in the coronary flow after practolol which completely abolished the increase in the myocardial O2 consumption as well as the positive inotropic and chronotropic effects produced by these compounds, while isoproterenol and salbutamol produced an increase. These results indicate that adrenergic beta-receptor exists in the coronary subserving a vasodilatation. However, the vasodilatation through this mechanism is of minor importance under physiological conditions and becomes completely masked in the presence of an overwhelmingly strong vasodilatation consequent to an increase in the myocardial O2 consumption.     

Role of endothelium in ischaemia-induced myocardial dysfunction of isolated working hearts: cardioprotection by activation of adenosine A(2A) receptors

1 This study aimed to determine the role of the vascular endothelium on recovery of contractile function following global low-flow ischaemia of guinea-pig isolated working hearts and the effects of adenosine analogues on this recovery. 2 Guinea-pig isolated spontaneously beating or paced working hearts were set up and coronary flow (CF), aortic output (AO) (as an index of cardiac function), heart rate (HR), left ventricular pressure (LVP) and dP/dt max recorded. The endothelium was either intact or removed by a blast of oxygen. 3 In spontaneously beating hearts, low-flow ischaemia for 30 min reduced CF and cardiac contractility (LVP, dP/dt max) but not AO. On reperfusion, CF, LVP and dP/dt max recovered, while AO fell precipitously followed by a gradual recovery, indicative of myocardial stunning. The effects of ischaemia did not differ between endothelium-intact and -denuded hearts, indicating no role of the endothelium in the changes observed. 4 The adenosine analogues, N6-cyclopentyladenosine (CPA, A1 selective), 5'-N-ethylcarboxamidoadenosine (NECA, two-fold A2 selective over A1) and 2-p-((carboxyethyl)-phenethylamino)-5'carboxamidoadenosine (CGS21680, A2A selective) were infused (3 x 10-7 M) from 10 min into the 30-min low-flow ischaemia of denuded hearts and during reperfusion. 5 CGS21680 increased CF and improved the postischaemic functional recovery, as measured by the AO. NECA and CPA were not cardioprotective. The A2A selective antagonist, ZM241385, attenuated the coronary vasodilatation by CGS21680 and abolished the improved recovery of AO on reperfusion. 6 Reperfusion of paced working hearts caused a dramatic fall in AO which failed to recover. Infusion of CGS21680 from 15 min into the ischaemic period produced vasodilatation but failed to restore AO, presumably because the ischaemic damage was irreversible. 7 Thus, the endothelium plays no role in myocardial dysfunction following low-flow global ischaemia and reperfusion of guinea-pig working hearts. The A2A adenosine receptor-selective agonist but not the non-selective A2 receptor agonist, NECA, attenuated ischaemia- and reperfusion-induced stunning. This was attributed to increased CF and was independent of the endothelium.     

Persistence of EDHF pathway and impairment of the nitric oxide pathway after chronic mercury chloride exposure in rats: mechanisms of endothelial dysfunction

Chronic mercury exposure impairs vascular function, leading to the depression of endothelium-dependent vasodilatation. Loss of the nitric oxide (NO) pathway has been implicated, but little is known about effects on other endothelial mediators. This study investigated the mechanisms of endothelial dysfunction in rats subjected to chronic mercury chloride exposure. The endothelium-dependent relaxation of rat aorta evoked by acetylcholine (ACh) and isoproterenol was impaired in a dose-dependent manner by chronic mercury chloride exposure. Endothelium-independent responses to sodium nitroprusside (SNP) were not affected by chronic mercury chloride exposure. In healthy vessels, ACh-induced relaxation was inhibited by L-N-nitroarginine methyl ester (L-NAME; 10(-4) M) and partially by glybenclamide (10(-5) M), indicating the involvement of NO and endothelium-derived hyperpolarizing factor (EDHF). In vessels from mercury-exposed rats, responses to ACh were insensitive to L-NAME but were significantly reduced by glybenclamide, indicating selective loss of NO-mediated relaxation. In vessels from mercury-exposed rats, responses to ACh were partially restored after treatment with the antioxidant, superoxide dismutase (SOD) and catalase, this effect was not seen when aorta from exposed group was incubated with L-NAME along with SOD and catalase indicating selective loss of NO-mediated vasodilatation and with no affect the EDHF-mediated component of relaxation. The results imply that chronic mercury exposure selectively impairs the NO pathway as a consequence of oxidative stress, while EDHF is able to maintain endothelium-dependent relaxation at a reduced level.     

Reduction of cerebral infarct volume by apocynin requires pretreatment and is absent in Nox2-deficient mice

Background and purpose:

Reactive oxygen species (ROS) derived from Nox2-containing reduced form of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity is reportedly detrimental in cerebrovascular disease. However, ROS generation by other Nox isoforms may have a physiological role. No Nox2-selective inhibitors have yet been identified, and thus it is unclear whether isoform non-selective Nox inhibitors would necessarily improve outcome after stroke. We assessed the effect of apocynin on cerebrovascular ROS production and also on outcome following cerebral ischaemia when administered either before ischaemia or after cerebral reperfusion. The involvement of Nox2-containing NADPH oxidase in the effects of apocynin was assessed using Nox2^−/− mice.

Experimental approach:

Transient cerebral ischaemia was induced by 0.5 h middle cerebral artery occlusion followed by 23.5 h reperfusion. Mice received apocynin (2.5 mg·kg⁻¹, i.p.) either 0.5 h before ischaemia or 1 h after reperfusion. In situ superoxide production after cerebral ischaemia-reperfusion was measured in brain sections of wild-type mice at 24 h using dihydroethidium fluorescence.

Key results:

Treatment with apocynin 0.5 h before ischaemia reduced total infarct volume, neurological impairment and mortality in wild-type but not Nox2^−/− mice. Conversely, treatment with apocynin 1 h after initiation of reperfusion had no protective effect. Cerebral ischaemia and reperfusion increased superoxide production in the brain at 24 h, and pretreatment but not posttreatment with apocynin reduced superoxide levels.

Conclusions and implications:

Apocynin improves outcome following stroke when administered before ischaemia in wild-type but not Nox2^−/− mice.     

Ischaemia enhances the role of Ca2+-activated K+ channels in endothelium-dependent and nitric oxide-mediated dilatation of the rat hindquarters vasculature

1. We compared the effects of the nitric oxide synthase inhibitor N(G)-nitro-L-arginine (L-NOARG) and tetraethylammonium (TEA), a blocker of large conductance Ca(2+)-activated K(+) (BK(Ca)) channels, on vasodilator responses to endothelium-dependent (acetylcholine; ACh) and -independent (sodium nitroprusside; SNP) vasodilators. The mechanism of the vasodilator responses was determined in rat hindquarters under normal conditions (sham ischaemia) and after 2 h ischaemia followed by reperfusion with physiological saline. 2. In sham ischaemia, the responses to ACh were significantly reduced by L-NOARG (1 mmol/L) and TEA (1 mmol/L) and there was a further reduction in response the presence of both agents. Dilator responses to SNP were significantly enhanced by L-NOARG, whereas TEA did not alter the SNP-induced vasodilatation when given either alone or in the presence of L-NOARG. 3. After ischaemia, L-NOARG caused a similar inhibition of ACh-induced dilatation to that observed in sham ischaemia. However, TEA alone or combined with L-NOARG caused a significantly greater inhibition of the ACh-induced vasodilatation after ischaemia than observed in the sham ischaemia group. Tetraethylammonium alone did not affect the responses to SNP, but it did attenuate the enhanced dilatation observed in the presence of L-NOARG. 4. In the rat hindquarters vasculature, both nitric oxide and the opening of TEA-sensitive K(+) channels contribute to ACh-induced endothelium-dependent dilatation. In addition, a TEA-sensitive mechanism was not involved in the SNP-induced dilatation under normal conditions but, after ischaemia, if there is a further inhibition of endogenous nitric oxide by L-NOARG, exogenous nitric oxide causes dilatation that is sensitive, in part, to TEA. Thus, the contribution of the opening of BK(Ca) channels to endothelium-dependent vasodilatation assumes greater importance after ischaemia and reperfusion. This may reflect an increased ability of nitric oxide or cGMP to open BK(Ca) channels after ischaemia.     

雷米普利对心肌梗死后心脏血管紧张素受体基因转录的影响

目的;在慢性给予血管紧张素酶抑制剂雷米普利后的大鼠中观察心肌梗死后早期心肌组织中血管紧张素Ⅱ受体基因转录的改变。方法：通过冠状动脉结扎建立大鼠ＭＩ模型,手术前１周即开始给予雷米普利或水,术后在存活大鼠心间隔组织的ＡｎｇⅡ受体ｍＲＮＡ水平。结果： 大鼠ＭＩ后心间隔组织中ＡＴ１和ＡＴ２受体ｍＲＮＡ水平升高,在１ｄ时达到高峰。     

Heat stress-induced protection of endothelial function against ischaemic injury is abolished by ATP-sensitive potassium channel blockade in the isolated rat heart

The protection conferred by heat stress (HS) against myocardial ischaemia-reperfusion injury, in terms of mechanical function preservation and infarct size reduction, is well documented and mechanisms underlying these effects have been extensively explored. However, the effect of HS on coronary circulation is less known. The aim of this study was thus to investigate the role of ATP-sensitive potassium (K(ATP)) channels in the protection against ischaemic injury afforded by HS to the coronary endothelial function. Twenty-four hours after whole body hyperthermia (42 degrees C for 15 min, H groups) or sham anaesthesia (Sham groups), isolated perfused rat hearts were subjected to a 15 min stabilization period followed by a 30 min infusion of either 0.3 microM glibenclamide (Gli, a K(ATP) channel blocker) or its vehicle (V). Hearts were then exposed to a low-flow ischaemia (30 min)-reperfusion (20 min) (I/R) or normally perfused (50 min), after which coronaries were precontracted with 0.1 microM U-46619. Finally, the response to the endothelium-dependent vasodilator, 5-hydroxytryptamine (5-HT, 10 microM) was compared to that of the endothelium-independent vasodilator, sodium nitroprusside (SNP, 3 microM). In hearts from Sham-V and Sham-Gli groups, I/R selectively diminished 5-HT-induced vasodilatation without affecting the vasodilatation to SNP. In V-treated groups, prior HS preserved the vasodilatation produced by 5-HT. This HS-induced protection was abolished by Gli treatment. In conclusion, these results suggest that K(ATP) channel activation contributes to the preservation of coronary endothelial function conferred by heat stress against ischaemic insult.     

辛伐他汀对急性心肌梗死大鼠血红素加氧酶-1的影响

目的探讨大鼠急性心肌梗死后心肌内血红素加氧酶-1(HO-1)水平变化及辛伐他汀对HO-1表达的影响。方法结扎♂SD大鼠冠状动脉左前降支建立心肌梗死模型,24 h后存活大鼠随机分为心肌梗死组(MI组)、辛伐他汀(Sim组)和假手术组(Sham组,只穿线不结扎)。Sim组以辛伐他汀40 mg.kg-1.d-1灌胃,MI组和Sham组以等体积生理盐水灌胃。术后24 h、7 d、28 d处死动物,RT-PCR及Western bolt测定心肌非梗死区HO-1 mRNA和蛋白表达水平,并测非梗死区心肌超氧化物岐化酶(SOD)活性、丙二醛(MDA)含量。结果HO-1 mRNA和蛋白表达水平均在心梗后24 h开始升高,7 d达峰,28 d恢复至基线水平。3个时间点MI组上述指标均高于Sham组;术后7 d和28 d Sim组上述指标均高于MI组(P<0.05)。随HO-1 mRNA和蛋白表达水平升高,SOD活性升高,MDA含量降低。结论心肌内HO-1水平在急性心肌梗死后28 d内呈现动态变化。辛伐他汀可诱导HO-1表达,发挥抗氧化损伤的心脏保护作用。     

Potential of calcitonin gene-related peptide in coronary heart disease

A subpopulation of capsaicin-sensitive cardiac C-fibre afferents co-store calcitonin gene-related peptide (CGRP), substance P and neurokinin A. CGRP exerts positive inotropic and chronotropic effects and is one of the most potent endogenous vasodilators yet discovered. A number of endogenous agents and conditions cause activation of cardiac C-fibre afferents with subsequent local release of CGRP. In myocardial ischaemia with its clinical manifestations angina pectoris and infarction, C-fibre afferents not only convey the sensation of pain, but there is also a local 'efferent' release of CGRP in the heart. After being released, CGRP causes coronary vasodilatation and attenuates the development of myocardial infarction. CGRP may thus represent an endogenous local myocardial protective substance with interesting clinical implications.     

Vasopressin effects on the coronary circulation after a short ischemia in anesthetized goats: role of nitric oxide and prostanoids

To examine the coronary effects of arginine-vasopressin during reperfusion after a short ischemia, left circumflex coronary artery flow was electromagnetically measured, and 15 min total occlusion of this artery followed by reperfusion was induced in anesthetized goats (five nontreated, five treated with the inhibitor of nitric oxide synthesis Nomega-nitro-L-arginine methyl ester (L-NAME) and five treated with the inhibitor of cyclooxygenase meclofenamate). The vasoactive drugs and L-NAME were intracoronarily injected, and meclofenamate by i.v. route. At 60 min of reperfusion, coronary vascular conductance was not changed significantly in nontreated and was decreased by 35% (P<0.01) in L-NAME-treated and by 30% (P<0.01) in meclofenamate-treated animals. During reperfusion, the coronary vasodilatation with acetylcholine (3-100 ng) and sodium nitroprusside (1-10 microg) was not altered in nontreated animals, and the vasodilatation with acetylcholine but not with sodium nitroprusside was partially decreased in L-NAME--but not in meclofenamate-treated animals. The vasoconstriction in response to arginine-vasopressin (0.03-0.3 microg) was increased during reperfusion in nontreated, was not changed in L-NAME-treated and was decreased in meclofenamate-treated animals. Therefore, it is suggested that during reperfusion after a short ischemia: (1) the coronary vasodilator reserve is preserved; (2) the coronary vasodilatation with acetylcholine is also preserved, but in this vasodilatation, the role of nitric oxide may be attenuated and prostanoids may be not involved; and (3) the coronary vasoconstriction with arginine-vasopressin is increased, probably due to both attenuation of the modulatory role of nitric oxide and the release of vasoconstrictor prostanoids.     

Investigation of mechanisms that mediate reactive hyperaemia in guinea-pig hearts: role of K(ATP) channels, adenosine, nitric oxide and prostaglandins

1. Reactive hyperaemia is a transient vasodilatation following a brief ischaemic period. ATP-dependent K(+) (K(ATP)) channels may be important in mediating this response, however it is unclear whether mitochondrial K(ATP) channels contribute to this in the heart. 2. We examined the involvement of K(ATP) channels and the relative role of mitochondrial channels as mediators of coronary reactive hyperaemia and compared them to mechanisms involving NO, prostaglandins and adenosine in the guinea-pig isolated heart. 3. Reactive hyperaemic vasodilatation (peak vasodilator response and flow debt repayment) were assessed after global zero-flow ischaemia (5 -- 120 s) in the presence of nitro-L-arginine methyl ester (L-NAME, 10(-5) M, n=9), 8-phenyltheophylline (8-PT, 10(-6) M, n=12) and indomethacin (10(-5) M, n=12). 4. Glibenclamide (10(-6) M, n=12) a non-selective K(ATP) channel inhibitor and 5-hydroxy-decanoic acid (5-HD, 10(-4) M, n=10) a selective mitochondrial K(ATP) channel inhibitor were also used. The specificity of the effects of glibenclamide and 5-HD (n=6 each) were confirmed using pinacidil (38 nmol -- 10 micromol) and diazoxide (42 nmol -- 2 micromol). Glibenclamide was most effective in blocking the hyperaemic response (by 87%, P<0.001) although 5-HD and 8-PT also had a marked effect (40% inhibition, P<0.001 and 32%, P<0.001, respectively). L-NAME and indomethacin had little effect. 5. Perfusion with L-NAME and glibenclamide significantly reduced baseline coronary flow (22%, P<0.01 and 33%, P<0.01) while 8-PT, indomethacin and 5-HD had no effect. 6. K(ATP) channels are the major mediators of the coronary reactive hyperaemic response in the guinea-pig. Although mitochondrial K(ATP) channels contribute, they appear less important than sarcolemmal channels.