Attenuation of reactive hyperemia caused by aspirin in canine coronary artery

Effects of intracoronary aspirin on coronary blood flow and reactive hyperemia were evaluated in closed-chest, anesthetized dogs. In 18 dogs the left circumflex coronary artery was cannulated and perfused by arterial blood at a constant pressure. Coronary blood flow was measured by an electromagnetic flowmeter. Intracoronary aspirin at doses of 5, 10, and 20 mg reduced coronary blood flow in a dose-dependent manner. Injection of aspirin at doses of 10 to 25 mg also inhibited reactive hyperemia following the coronary occlusion for fifteen seconds. The mean peak flow ratio was reduced from 2.13 +/- 0.42 to 1.75 +/- 0.35 (p less than 0.005). The increment of coronary blood flow provoked by intracoronary arachidonic acid at doses of 150 to 300 micrograms was almost entirely inhibited by the pretreatment of the coronary artery with aspirin. The authors conclude that aspirin increases coronary arterial resistance in a dose-dependent manner and also restricts the maximal dilating capacity, possibly by inhibition of prostacyclin synthesis.     

Blockade of ATP-sensitive potassium channels prevents myocardial preconditioning in dogs.

Single or multiple brief periods of ischemia (preconditioning) have been shown to protect the myocardium from infarction after a subsequent more prolonged ischemic insult. To test the hypothesis that preconditioning is the result of opening ATP-sensitive potassium (KATP) channels, a selective KATP channel antagonist, glibenclamide, was administered before or immediately after preconditioning in barbital-anesthetized open-chest dogs subjected to 60 minutes of left circumflex coronary artery (LCX) occlusion followed by 5 hours of reperfusion. Preconditioning was elicited by 5 minutes of LCX occlusion followed by 10 minutes of reperfusion before the 60-minute occlusion period. Glibenclamide (0.3 mg/kg i.v.) or vehicle was given 10 minutes before the initial ischemic insult in each of four groups. In a fifth group, glibenclamide was administered immediately after preconditioning. In a final series (group 6), a selective potassium channel opener, RP 52891 (10 micrograms/kg bolus and 0.1 micrograms/mg/min i.v.) was started 10 minutes before occlusion and continued throughout reperfusion. Transmural myocardial blood flow was measured at 30 minutes of occlusion, and infarct size was determined by triphenyltetrazolium staining and expressed as a percent of the area at risk. There were no significant differences in hemodynamics, collateral blood flow, or area at risk between groups. The ratio of infarct size to area at risk in the control group (28 +/- 6%) was not different from the group pretreated with glibenclamide in the absence of preconditioning (31 +/- 6%). Preconditioning produced a marked reduction (p less than 0.002) in infarct size (28 +/- 6% to 6 +/- 2%), whereas glibenclamide administered before or immediately after preconditioning completely abolished the protective effect (28 +/- 6% and 30 +/- 8%, respectively). RP 52891 also produced a significant (p less than 0.03) reduction (28 +/- 6% to 13 +/- 3%) in infarct size. These results suggest that myocardial preconditioning in the canine heart is mediated by activation of KATP channels and that these channels may serve an endogenous myocardial protective role.     

Adenosine metabolism in canine myocardial reactive hyperemia

In pentobrabital-anesthetized open chest dogs, myocardial adenosine content is elevated by 5 or 15 seconds of left coronary artery occlusion and falls exponentially to control levels during reactive hyperemia. The rate constants for adenosine dissipation are (mean +/- SEM): -0.08 +/- 0.01 and -0.034 +/- 0.007 sec-1 after 5- and 15-second occlusion, respectively. Kinetic analysis of the reactive hyperemia flow curves (Circ Res 14/15 (suppl I): 81-85, 1963) predicts rates of -0.069 +/- 0.009 sec-1 and -0.04 +/- 0.009 sec-1, indicating that changes in adenosine levels can account for the way coronary flow changes during this response. The log (dose-) response curve relating reactive hyperemia flow to tissue adenosine concentration has a steeper slope and is half-maximal at a lower adenosine concentration than the dose-response curve obtained by intracoronary infusions of adenosine in oxygenated hearts, indicating that the coronary vasoactivity of adenosine is enhanced during reactive hyperemia. This could explain why theophylline antagonizes the coronary vasocilatory effect of adenosine in oxygenated hearts but has relatively little effect on reactive hyperemia.     

Comparison of the effect of the ATP-sensitive potassium channel opener YM934 with that of nitroglycerin on impaired coronary circulation in dogs

We compared the effect of an ATP-sensitive potassium channel opener, YM934, with that of nitroglycerin (NTG) on impaired coronary circulation in dogs. Coronary stenosis was produced in 7 dogs by placing a hydraulic occluder around the proximal left circumflex coronary (LCx) artery and abolishing reactive hyperemia to compromise the LCx flow. The following parameters were measured: the aortic pressure, LCx flow velocity, LCx vessel diameter, LCx peripheral pressure, and segment length in the LCx area. Subsequently, we occluded the LCx artery for 15 seconds and measured the recovery-interval (time required for the segment shortening to return to the preocclusion value). The measurements were recorded under three study conditions: (1) at baseline without LCx stenosis; (2) with LCx stenosis under NTG infusion (3 microg/Kg/min); and (3) with LCx stenosis after intravenous administration of YM934 (0.3 microg/kg). The heart rate and aortic pressure were similar under the three study conditions. Mean LCx flow velocity and segment shortening did not significantly change either. However, LCx peripheral pressure decreased after the induction of stenosis (P < 0.05) and showed no response to either NTG or YM934. YM934 administration significantly increased LCx flow in the presence of LCx stenosis, (P < 0.05), whereas NTG infusion did not. YM934 significantly shortened the recovery-interval of the segment shortening after 15-sec LCx occlusion (P < 0.05), whereas NTG did not. These findings suggest that YM934 improves coronary blood flow and prevents myocardial ischemic damage in severely impaired coronary circulation.     

Sarcoplasmic ATP-sensitive potassium channel blocker HMR1098 protects the ischemic heart: implication of calcium, complex I, reactive oxygen species and mitochondrial ATP-sensitive potassium channel

The aim of this study was to investigate the effects of HMR1098, a selective blocker of sarcolemmal ATP-sensitive potassium channel (sarcK(ATP)), in Langendorff-perfused rat hearts submitted to ischemia and reperfusion. The recovery of heart hemodynamic and mitochondrial function, studied on skinned fibers, was analyzed after 30-min global ischemia followed by 20-min reperfusion. Infarct size was quantified on a regional ischemia model after 2-h reperfusion. We report that the perfusion of 10 microM HMR1098 before ischemia, delays the onset of ischemic contracture, improves recovery of cardiac function upon reperfusion, preserves the mitochondrial architecture, and finally decreases infarct size. This HMR1098-induced cardioprotection is prevented by 1 mM 2-mercaptopropionylglycine, an antioxidant, and by 100 nM nifedipine, an L-type calcium channel blocker. Concomitantly, it is shown that HMR1098 perfusion induces (i) a transient and specific inhibition of the respiratory chain complex I and, (ii) an increase in the averaged intracellular calcium concentration probed by the in situ measurement of indo-1 fluorescence. Finally, all the beneficial effects of HMR1098 were strongly inhibited by 5-hydroxydecanoate and abolished by glibenclamide, two mitoK(ATP) blockers. This study demonstrates that the HMR1098-induced cardioprotection occurs indirectly through extracellular calcium influx, respiratory chain complex inhibition, reactive oxygen species production and mitoK(ATP) opening. Taken together, these data suggest that a functional interaction between sarcK(ATP) and mitoK(ATP) exists in isolated rat heart ischemia model, which is mediated by extracellular calcium influx.     

Effect of ATP-sensitive potassium channel inhibition on resting coronary vascular responses in humans

Experimental data suggest that vascular ATP-sensitive potassium (K(ATP)) channels regulate coronary blood flow (CBF), but their role in regulating human CBF is unclear. We sought to determine the contribution of K(ATP) channels to resting conduit vessel and microvascular function in the human coronary circulation. Twenty-five patients (19 male/6 female, aged 56 +/- 12 years) were recruited. Systemic and coronary hemodynamics were assessed in 20 patients before and after K(ATP) channel inhibition with graded intracoronary glibenclamide infusions (4, 16, and 40 microg/min), in an angiographically smooth or mildly stenosed coronary artery following successful elective percutaneous coronary intervention to another vessel. Coronary blood velocity was measured with a Doppler guidewire and CBF calculated. Adenosine-induced hyperemia was determined following bolus intracoronary adenosine injection (24 microg). Time control studies were undertaken in 5 patients. Compared with vehicle infusion (0.9% saline), glibenclamide reduced resting conduit vessel diameter from 2.5 +/- 0.1 to 2.3 +/- 0.1 mm (P<0.01), resting CBF by 17% (P=0.05), and resting CBF corrected for rate pressure-product by 18% (P=0.01) in a dose-dependent manner. A corresponding 24% increase in coronary vascular resistance was noted at the highest dose (P<0.01). No alteration to resting CBF was noted in the time control studies. Glibenclamide reduced peak adenosine-induced hyperemia (P=0.01) but did not alter coronary flow reserve. Plasma insulin increased from 5.6 +/- 1.2 to 7.6 +/- 1.3 mU/L (P=0.02); however, plasma glucose was unchanged. Vascular K(ATP) channels are involved in the maintenance of basal coronary tone but may not be essential to adenosine-induced coronary hyperemia in humans.     

Altered effects of potassium channel modulation in the coronary circulation in experimental hypercholesterolemia

OBJECTIVE: To evaluate the role of potassium channels in the regulation of coronary hemodynamics in experimental hypercholesterolemia. BACKGROUND: Potassium (K(+)) channels play an important role in coronary vasoregulation. It has previously been demonstrated that experimental hypercholesterolemia is associated with altered coronary vasomotion; however, the role of K(+) channels in modulating coronary blood flow in this pathophysiologic state has not been evaluated. METHODS AND RESULTS: Pinacidil (group 1, n=5) at 2 microg/kg per min, glibenclamide (group 2, n=5), or N-monomethyl-L-arginine (LNMMA) (group 3, n=4) at 50 microg/kg per min were infused into the left anterior descending artery of pigs prior to and following 10 weeks of 2% cholesterol diet. After 10 weeks of cholesterol feeding, intracoronary pinacidil resulted in a significant increase in coronary blood flow (CBF) and coronary artery diameter (CAD) compared to the normolipidemic state (111+/-10 versus 59+/-12%, and 6+/-1.1 versus 2.7+/-1.0%, respectively, P<0.05 for both comparisons), whereas intracoronary glibenclamide resulted in a significant decrease in CBF and CAD compared to the normolipidemic state (-17+/-5 versus 5+/-6%, and -0.8+/-1.4 versus 3.6+/-1.6%, respectively, P<0.05 for both comparisons). The effect of intracoronary LNMMA on CBF and CAD was significantly attenuated after 10 weeks of cholesterol feeding as compared to the normolipidemic state (-47+/-5.4 versus -0.8+/-6.8%, and -19.4+/-5.7 versus -2.3+/-3.3%, respectively, P<0.05 for both comparisons). Furthermore, pretreatment with intracoronary LNMMA did not alter the CBF response to pinacidil in normal pigs (group 4, n=4) (57.4+/-19 versus 59+/-12%, P=NS). CONCLUSIONS: The current study demonstrates an enhanced effect of coronary K(+) channel modulation and confirms the attenuated basal NO activity previously reported in experimental hypercholesterolemia. Acute withdrawal of basal NO activity alone, however, does not explain the enhanced effect of coronary K(+) channel modulation. These findings underscore the importance of the K(+) channel pathway in the regulation of coronary vasomotor tone in pathophysiologic states.     

Segmental alpha-receptor-mediated vasoconstriction in the canine coronary circulation.

Recent studies from this laboratory have indicated that sympathetic alpha-receptor-mediated coronary vasoconstriction can compete with local metabolic vasodilation to reduce the oxygen supply to the myocardium. In vitro studies from other laboratories on isolated coronary vessel strips suggest that large epicardial vessels are the dominant site of adrenergic alpha-receptor activity. In this study we used anesthetized, open-chest dogs to test the hypothesis that alpha-receptor-mediated vasoconstriction occurs predominantly in epicardial vessels, which are partially removed from the metabolic milieu in the myocardium. Adrenergic beta-receptor blockade was achieved by propranolol (3 mg/kg, iv). The circumflex coronary artery was pump-perfused at constant pressure to minimize passive changes in large vessel resistance. Pressure was measured at the tip of the perfusion cannula sealed in the circumflex artery, and in an apical branch of the circumflex artery. Large vessel resistance was calculated as the pressure gradient along the vessel segment divided by the coronary flow. Intracoronary injections of nitroglycerin were used as an independent measure of the vasomotor responsiveness of the large vessel segment. Adrenergic alpha-receptor activation was produced by intracoronary bolus injections of norepinephrine and by electrical stimulation of the left stellate ganglion. Alpha-receptor stimulation caused an increase in total coronary vascular resistance; however, the relative increase in the resistance of the large vessel was only about 60% of that seen for the entire coronary bed. These data suggest that, contrary to the proposed hypothesis, adrenergic alpha-receptor-mediated vasoconstriction in the large coronary vessels is not proportionally greater than that observed in the total coronary vascular bed.     

Phasic contractions of canine and human coronary arteries induced by potassium channel blockers

To gain insight into mechanisms underlying phasic coronary vasospasm in patients with variant angina pectoris, we studied whether phasic contractions could be induced in isolated canine and human coronary arteries by agents which block potassium channels. Phasic contractions of canine coronary arteries were always induced by 3,4-diaminopyridine (10(-2) M) and less frequently by 4-aminopyridine (10(-2) M). These agents also caused phasic contractions in human, swine and monkey coronary arteries and in canine basilar, carotid, renal and femoral arteries. The cycle length of phasic coronary contractions ranged from 30 sec to 1 hour, and the developed tension was 2.5 times greater than for potassium contractions. The contractions continued for more than 11 hours. Morphologically, perinuclear vacuolization, a characteristic change of vasospasm, appeared in the coronary smooth muscles. The phasic contractions were not eliminated by tetrodotoxin, atropine, phentolamine or yohimbine, but they were eliminated by nicorandil which activates potassium channels and nifedipine which blocks slow calcium channels. The results indicate that potassium channel blockers can induce phasic arterial contractions.     

Role of ATP-sensitive potassium channels in coronary microvascular autoregulatory responses

The purpose of the present study was to test the hypothesis that ATP-sensitive potassium channels mediate autoregulatory vasodilatation of coronary arterioles in vivo. Experiments were performed in 23 open-chest anesthetized dogs. Coronary arterial microvascular diameters were directly measured with fluorescence microangiography using an intravital microscope and stroboscopic epi-illumination synchronized to the cardiac cycle. A mild coronary stenosis (perfusion pressure = 60 mm Hg), a critical coronary stenosis (perfusion pressure = 40 mm Hg), and complete coronary artery occlusion were produced with an occluder around the left anterior descending coronary artery in the presence or absence of glibenclamide (10(-5) M, topically), which inhibits ATP-sensitive potassium channels, or of vehicle. During topical application of vehicle (0.01% dimethyl sulfoxide), there was dilatation of small (less than 100 microns diameter) arterioles during reductions in perfusion pressure (percent change in diameter: 6.7 +/- 1.5%, 11.7 +/- 3.5%, and 10.4 +/- 5.1% during mild stenosis, critical stenosis, and complete occlusion, respectively). In the presence of glibenclamide, arteriolar dilatations during coronary stenoses and occlusions were abolished. Glibenclamide did not affect responses of arterioles greater than 100 microns. Glibenclamide did not alter microvascular responses to nitroprusside. These data suggest that ATP-sensitive potassium channels play an important role in determining the coronary microvascular response to reductions in perfusion pressure.     

纳他卡林对鼠脑线粒体ATP敏感性钾通道的开放作用

目的 探讨纳他卡林对脑线粒体ATP敏感性钾通道的影响.方法急性分离大鼠脑线粒体,采用Clark氧电极法测定纳他卡林对线粒体耗氧速率的影响;采用紫外分光光度法测定纳他卡林对线粒体悬液在540 nm处的吸光值的影响,用以监测线粒体基质容积的变化.结果纳他卡林可使脑线粒体的耗氧速率增加(7.58±2.76)%(P＜ 0.05...     

Potassium accumulation in the globally ischemic mammalian heart. A role for the ATP-sensitive potassium channel

We investigated the contribution of opening of the ATP-sensitive K+ channel to extracellular accumulation of K+ during ischemia with the use of glibenclamide, a specific blocker of this K+ channel. To characterize the electrophysiological effects of glibenclamide during metabolic inhibition (by either application of dinitrophenol or hypoxia) we performed patch-clamp studies in isolated membrane patches of guinea pig myocytes and in intact guinea pig myocytes and studied action potential parameters in isolated superfused guinea pig papillary muscle. We studied the effect of glibenclamide on extracellular accumulation of K+ and H+ in isolated retrogradely perfused globally ischemic hearts of rat, guinea pig, and rabbit. Experimental evidence is presented that supports the conclusions that glibenclamide 1) effectively blocks open K+ATP channels, 2) reverses the dinitrophenol-induced increase of the outward current and prevents the hypoxia-induced shortening of the action potential, 3) decreases the rate of K+ accumulation during the first minutes of ischemia in stimulated hearts, an effect which was entirely absent in quiescent hearts, and 4) does not influence the rate and extent of ischemia-induced extracellular acidification.     

Effect of diltiazem on coronary reactive hyperemia in patients with flow-limiting coronary artery stenosis

The acute effects of diltiazem on coronary reactive hyperemia were studied in 12 patients with flow-limiting coronary stenosis. Reactive hyperemia was elicited by injection of 8 ml contrast medium into the left coronary artery, while coronary sinus blood flow and left ventricular and aortic pressures were continuously recorded. Relative magnitude of hyperemia was estimated by the ratio of coronary flow at peak hyperemia to baseline flow (hyperemic ratio). Coronary resistance was calculated as the ratio between mean aortic pressure minus left ventricular mean diastolic pressure and coronary sinus blood flow. The 12 patients studied had flow-limiting coronary stenosis since their hyperemic ratio was significantly restrained when compared to that of seven control subjects (1.45 +/- 0.17 vs 2.02 +/- 0.24, respectively; p less than 0.001). The intravenous infusion of diltiazem (0.30 mg X kg-1) reduced heart rate, mean aortic pressure, and myocardial oxygen consumption (all p less than 0.001). After diltiazem the hyperemic ratio was blunted when compared to the basal state (1.36 +/- 0.15 vs 1.45 +/- 0.17, respectively; p less than 0.05), and hyperemia volume was reduced (-33%; p less than 0.001). The decrease in coronary resistance at peak hyperemia was also reduced from -30 +/- 8% to -25 +/- 8% (p less than 0.05). We conclude that diltiazem blunts coronary reactive hyperemia in patients with demonstrated flow-limiting coronary stenosis. This reduction of coronary flow response to a hyperemic stimulus could favorably influence blood flow distribution in patients with significant coronary stenosis.     

Manifestation of coronary subclavian steal phenomenon using reactive hyperemia in the ipsilateral forearm

Coronary subclavian steal syndrome (CSSS) is a coronary steal phenomenon secondary to subclavian artery stenosis in patients who have undergone coronary bypass surgery with the internal thoracic artery. Most commonly, CSSS is diagnosed angiographically. Our case emphasizes that stress ultrasound assessment using reactive hyperemia in the ipsilateral arm elicits a functional diagnosis of CSSS.     

一个2型糖尿病家系ATP敏感性钾通道基因突变分析

目的了解ATP敏感性钾通道（KATP）基因突变在一个2型糖尿病（T2DM）家系中的发生情况。方法提取家系成员的外周血DNA，用PCR扩增磺酰脲类受体1（SUR-1）基因第16、18、31外显子和KIR 6.2基因，用单链构象多态性分析（SSCP）检测PCR产物，对SSCP电泳结果异常者进行DNA序列分析。结果（1）在17名家系成员中，未检测到SUR-1基因第18号外显子ACC→ACT和第31外显子AGG→AGA突变；（2）SUR-1基因第16号外显子-3C→T的T等位基因频率为65％，比普通T2DM人群高8％；（3）KIR 6.2基因E23K的K等位基因频率38％，比普通T2DM人群低3％。结论SUR-1基因第16号外显子-3C→T多态性可能与饮食、环境等因素共同作用，参与该家系T2DM的发生和发展。