Coronary Vasodilator Response Research Articles

Cardioprotective actions of nitroxyl donor Angeli's salt are preserved in the diabetic heart and vasculature in the face of nitric oxide resistance

Background and PurposeThe risk of fatal cardiovascular events is increased in patients with type 2 diabetes mellitus (T2DM). A major contributor to poor prognosis is impaired nitric oxide (NO•) signalling at the level of tissue responsiveness, termed NO• resistance. This study aimed to determine if T2DM promotes NO• resistance in the heart and vasculature and whether tissue responsiveness to nitroxyl (HNO) is affected.Experimental ApproachAt 8 weeks of age, male Sprague–Dawley rats commenced a high‐fat diet. After 2 weeks, the rats received low‐dose streptozotocin (two intraperitoneal injections, 35 mg·kg−1, over two consecutive days) and continued on the same diet. Twelve weeks later, isolated hearts were Langendorff‐perfused to assess responses to the NO• donor diethylamine NONOate (DEA/NO) and the HNO donor Angeli's salt. Isolated mesenteric arteries were utilised to measure vascular responsiveness to the NO• donors sodium nitroprusside (SNP) and DEA/NO, and the HNO donor Angeli's salt.Key ResultsInotropic, lusitropic and coronary vasodilator responses to DEA/NO were impaired in T2DM hearts, whereas responses to Angeli's salt were preserved or enhanced. Vasorelaxation to Angeli's salt was augmented in T2DM mesenteric arteries, which were hyporesponsive to the relaxant effects of SNP and DEA/NO.Conclusion and ImplicationsThis is the first evidence that inotropic and lusitropic responses are preserved, and NO• resistance in the coronary and mesenteric vasculature is circumvented, by the HNO donor Angeli's salt in T2DM. These findings highlight the cardiovascular therapeutic potential of HNO donors, especially in emergencies such as acute ischaemia or heart failure.

Sex differences in the coronary vascular response to combined chemoreflex and metaboreflex stimulation in healthy humans.

What is the central question of this study? Coronary blood flow in healthy humans is controlled by both local metabolic signalling and adrenergic activity: does the integration of these signals during acute hypoxia and adrenergic activation differ between sexes? What are the main findings and its importance? Both males and females exhibit an increase in coronary blood velocity in response to acute hypoxia, a response that is constrained by adrenergic stimulation in males but not females. These findings suggest that coronary blood flow control differs between males and females. Coronary hyperaemia is mediated through multiple signalling pathways, including local metabolic messengers and adrenergic stimulation. This study aimed to determine whether the coronary vascular response to adrenergic stressors is different between sexes in normoxia and hypoxia. Young, healthy participants (n=32; 16F) underwent three randomized trials of isometric handgrip exercise followed by post-exercise circulatory occlusion (PECO) to activate the muscle metaboreflex. End-tidal was controlled at (1) normoxic levels throughout the trial, (2) 50mmHg for the duration of the trial (hypoxia trial), or (3) 50mmHg only during PECO (mixed trial). Mean left anterior descending coronary artery velocity (LADVmean ; transthoracic Doppler echocardiography), heart rate and blood pressure were assessed at baseline and during PECO. In normoxia, there was no change in LADVmean or cardiac workload induced by PECO in males and females. Acute hypoxia increased baseline LADVmean to a greater extent in males compared with females (P<0.05), despite a similar increase in cardiac workload. The change in LADVmean induced by PECO was similar between sexes in normoxia (P=0.31), greater in males during the mixed trial (male: 12.8 (7.7) cm/s vs. female: 8.1 (6.3) cm/s; P=0.02) and reduced in males but not females in acute hypoxia (male: -4.8 (4.5) cm/s vs. female: 0.8 (6.2) cm/s; P=0.006). In summary, sex differences in the coronary vasodilatory response to hypoxia were observed, and metaboreflex activation during hypoxia caused a paradoxical reduction in coronary blood velocity in males but not females.

Abstract P405: Cardioprotective Actions Of Nitroxyl Donor Angeli's Salt Are Preserved In The Diabetic Heart And Vasculature In The Face Of Nitric Oxide Resistance

Introduction: The risk of fatal cardiovascular events is increased in patients with type 2 diabetes mellitus (T2DM). A major contributor to poor prognosis is impaired nitric oxide (NO•) signalling at the level of tissue responsiveness, termed NO• resistance. Nitroxyl (HNO) induces positive inotropic and lusitropic effects in healthy and failing hearts. Hypothesis: We hypothesised that in a rodent model, T2DM will promote, and HNO will circumvent, NO• resistance in the myocardium and coronary vasculature. Methods: At 8 weeks of age, male Sprague-Dawley rats commenced a high-fat diet. After two weeks, the rats received low-dose streptozotocin (two intraperitoneal injections, 35 mg/kg, over two consecutive days), and continued the diet. Twelve weeks later, hearts were Langendorff-perfused to assess responses to the NO• donor diethylamine NONOate (DEA/NO) and the HNO donor Angeli’s salt. Results: Inotropic, lusitropic and coronary vasodilator responses to DEA/NO were impaired, and responses to Angeli’s salt were preserved or enhanced, in T2DM hearts compared with non-diabetic hearts. Conclusions: This is the first evidence that inotropic and lusitropic responses are preserved, and NO• resistance in the coronary vasculature is circumvented, by the HNO donor Angeli’s salt in T2DM. These findings highlight the cardiovascular therapeutic potential of HNO donors, especially in cardiac emergencies such as acute ischaemia or heart failure. Figure 1. Dose-response curves and maximal responses to DEA/NO or Angeli's salt in diabetic or non-diabetic hearts. (A-C) LV+dP/dt, (D-F) LV-dP/dt and (G-I) coronary flow rate. Data expressed as change from baseline (denoted by Δ), mean ± SEM. Data analysed by two-way RM ANOVA with Sidak's post-hoc test. *P&lt;0.05 vs. non-diabetic. LV, left ventricular; LV+dP/dt, maximal rate of rise in LV pressure; LV-dP/dt, maximal rate of fall in LV pressure.

New Insight Into the Cardioprotective Effects of Allium ursinum L. Extract Against Myocardial Ischemia-Reperfusion Injury.

This study aimed to estimate the effects of increasing doses of Allium ursinum methanol extract on cardiac ischemia/reperfusion injury (I/R) with a special emphasis on the role of oxidative stress. Fifty rats were randomly divided into five groups (10 animals per group) depending on the applied treatment as follows: sham, rats who drank only tap water for 28 days and hearts were retrogradely perfused for 80 min without I/R injury, I/R, rats who drank only tap water for 28 days and hearts were exposed to ex vivo I/R injury and rats who consumed increasing doses of A. ursinum 125, 250, and 500 mg/kg for 28 days before I/R injury. Hearts from all rats were isolated and retrogradely perfused according to the Langendorff technique. Parameters of oxidative stress were spectrophotometrically measured in blood, coronary venous effluent, and heart tissue samples. Intake of wild garlic extract for 28 days significantly contributed to the recovery of cardiac function, which was reflected through preserved cardiac contractility, systolic function, and coronary vasodilatory response after ischemia. Also, wild garlic extract showed the potential to modulate the systemic redox balance and stood out as a powerful antioxidant. The highest dose led to the most efficient decrease in cardiac oxidative stress and improve recovery of myocardial function after I/R injury. We might conclude that wild garlic possesses a significant role in cardioprotection and strong antioxidant activity, which implicates the possibility of its use alone in the prevention or as adjuvant antioxidant therapy in cardiovascular diseases (CVD).

Obesity decreases the contribution of Kv channels to hypoxic coronary vasodilation

Background and Hypothesis: Our group previously demonstrated that reductions in the functional expression of voltage-dependent K+ (Kv) channels contribute to impaired metabolic control of coronary blood flow in the setting of obesity. This study tested the hypothesis that obesity diminishes the contribution of Kv channels to coronary vasodilation in response to hypoxemia.&#x0D; Experimental Design or Project Methods: Control lean (n = 7) and obese (n = 5) swine were anesthetized and the heart exposed via left lateral thoracotomy. Coronary blood flow was measured in response to hypoxemia, before and after inhibition of Kv channels by 4-aminopyridine (4-AP; 0.3 mg/kg, iv), by a flow probe placed about the left anterior descending coronary artery. Hypoxemia was induced by progressive increases in the amount of nitrogen introduced into the ventilator. Arterial blood samples were obtained at each reduction in arterial oxygenation via a catheter placed in the femoral artery.&#x0D; Results: Blood pressure decreased from ~88 ± 5 mmHg to ~68 ± 6 mmHg (P = 0.01) as arterial PO2 was reduced below 50 mmHg in both lean and obese swine (P = 0.51). In lean swine, coronary flow progressively increased from ~0.6 to &gt;3.0 ml/min/g as arterial PO2 was reduced. This response was decreased by ~40% in obese swine and by ~30% in lean swine treated with 4-AP. Administration of 4AP had no effect on coronary flow in obese swine.&#x0D; Conclusion and Potential Impact: These data support that Kv channels contribute to increases in coronary flow in response to hypoxemia in lean swine and that reductions in Kv channel function contribute to impaired hypoxic coronary vasodilation in obese swine. We propose that therapeutic targeting of obesity associated pathways (angiotensin-aldosterone system) known to influence K+ channel expression could improve coronary microvascular function and cardiovascular outcomes in subjects with obesity. Supported by R01 HL136386; T35 HL 110854.

Peripheral Microvascular Function Reflects Coronary Vascular Function.

Objectives- Coronary endothelial dysfunction is a precursor of atherosclerosis and adverse outcomes. Whether endothelial dysfunction is a localized or generalized phenomenon in humans remains uncertain. We simultaneously measured femoral and coronary vascular function with the hypothesis that peripheral vascular endothelial function will be reflective of coronary endothelial function. Approach and Results- Eighty-five subjects underwent coronary angiography for evaluation of chest pain or abnormal stress tests. Endothelium-dependent and -independent vascular function were measured using intracoronary and intrafemoral infusions of acetylcholine and sodium nitroprusside, respectively. Coronary flow reserve was assessed using intracoronary adenosine infusion. Flow velocity was measured in each circulation using a Doppler wire (FloWire, EndoSonics). Coronary vascular resistance and femoral vascular resistance were calculated as mean arterial pressure (mm Hg)/coronary blood flow (mL/min) and mean arterial pressure (mm Hg)/femoral average peak velocity (cm/s), respectively. Mean age was 53±11 years, 37% were female, 44% had hypertension, 12% had diabetes mellitus, and 38% had obstructive coronary artery disease. There was a correlation between the change in femoral vascular resistance with acetylcholine and acetylcholine-mediated changes in both the coronary vascular resistance ( r=0.27; P=0.014) and in the epicardial coronary artery diameter ( r=-0.25; P=0.021), indicating that subjects with normal endothelial function in the femoral circulation had normal endothelial function in the coronary epicardial and microcirculation and vice versa. The coronary vasodilator response to adenosine also correlated with the femoral vasodilatation with acetylcholine ( r=0.4; P=0.0002). There was no correlation between the coronary and femoral responses to sodium nitroprusside. Conclusions- Endothelial functional changes in the peripheral and coronary circulations were modestly correlated. Thus, peripheral microvascular endothelial function reflects endothelium-dependent coronary epicardial and microvascular function and the coronary flow reserve. Visual Overview- An online visual overview is available for this article.

Protective Effects of Galium verum L. Extract against Cardiac Ischemia/Reperfusion Injury in Spontaneously Hypertensive Rats.

Galium verum L. (G. verum, lady's bedstraw) is a perennial herbaceous plant, belonging to the Rubiaceae family. It has been widely used throughout history due to multiple therapeutic properties. However, the effects of this plant species on functional recovery of the heart after ischemia have still not been fully clarified. Therefore, the aim of our study was to examine the effects of methanol extract of G. verum on myocardial ischemia/reperfusion (I/R) injury in spontaneously hypertensive rats (SHR), with a special emphasis on the role of oxidative stress. Rats involved in the research were divided randomly into two groups: control (spontaneously hypertensive rats (SHR)) and G. verum group, including SHR rats treated with the G. verum extract (500 mg/kg body weight per os) for 4 weeks. At the end of the treatment, in vivo cardiac function was assessed by echocardiography. Rats were sacrificed and blood samples were taken for spectrophotometric determination of systemic redox state. Hearts from all rats were isolated and retrogradely perfused according to the Langendorff technique. After a stabilization period, hearts were subjected to 20-minute ischemia, followed by 30-minute reperfusion. Levels of prooxidants were spectrophotometrically measured in coronary venous effluent, while antioxidant enzymes activity was assessed in heart tissue. Cell morphology was evaluated by hematoxylin and eosin (HE) staining. 4-week treatment with G. verum extract alleviated left ventricular hypertrophy and considerably improved in vivo cardiac function. Furthermore, G. verum extract preserved cardiac contractility, systolic function, and coronary vasodilatory response after ischemia. Moreover, it alleviated I/R-induced structural damage of the heart. Additionally, G. verum extract led to a drop in the generation of most of the measured prooxidants, thus mitigating cardiac oxidative damage. Promising potential of G. verum in the present study may be a basis for further researches which would fully clarify the mechanisms through which this plant species triggers cardioprotection.

Chronically Increased Aldosterone In Vivo Attenuates Coronary Vasodilation to Adenosine

Adenosine‐induced coronary vasodilation is an important cardioprotective mechanism during cardiac hypoxia and ischemia and is utilized clinically for the determination of coronary flow reserve (CFR), an independent predictor of cardiac mortality. Impaired coronary vasodilation to adenosine is more common in diseases associated with inappropriate activation of the renin‐angiotensin‐aldosterone system (RAAS) and recent evidence indicates that systemic blockade of mineralocorticoid receptors (MR) improves CFR in patients with diabetes. The mechanisms underlying RAAS‐dependent attenuation of coronary adenosine‐induced vasodilation, however, remain unclear. Therefore, we hypothesized that chronic infusion of the MR agonist aldosterone would blunt coronary adenosine‐mediated vasodilation and that this would involve reduced adenosine type 2A (A2A) receptor‐dependent vasodilation. Studies were performed using 13–15 week old male C57BL/6J mice infused with either vehicle (95% EtOH in saline) or a subpressor dose of aldosterone (250 μg/kg/d) chronically for 4 weeks via osmotic minipump. After infusion, left ventricular coronary arteries were dissected and function was assessed by wire myography. Chronic infusion of aldosterone raised circulating aldosterone concentrations but did not increase heart weight. Aldosterone infusion blunted coronary vasodilation to adenosine, particularly within the range of adenosine concentrations relevant to those in vivo during cardiac hypoxia (1–10 μM), but did not reduce maximal adenosine‐induced vasodilation. Coronary vasodilation to the endothelium‐dependent vasodilator acetylcholine was also blunted by aldosterone infusion. Additional studies revealed that coronary adenosine‐induced vasodilation in the mouse is entirely dependent on activation of K+ channels and that selective activation of adenosine type 2B (A2B) receptors with BAY 60–6583 induces greater vasodilation that activation of A2A receptors with CGS‐21680. Chronic aldosterone infusion blunted coronary vasodilation in response to selective A2A, but not selective A2B, activation. RT‐PCR revealed no difference in aortic A2A and A2B gene expression. Taken together, our data demonstrate that chronic elevations of aldosterone blunt coronary vasodilation to adenosine via impaired A2A‐dependent vasodilation. This aldosterone‐dependent blunting of adenosine‐mediated vasodilation has implications for cardiac injury in response to hypoxia in states associated with inappropriate RAAS activation such as obesity and diabetes.Support or Funding InformationFunded by VHA BLR&amp;D BX002030 (SBB) and a STRIDE Undergraduate Summer Research Fellowship (MK) supported by the American Physiological Society and NIH NHLBI R25 HL115473‐01.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Uridine Adenosine Tetraphosphate-Induced Coronary Relaxation Is Blunted in Swine With Pressure Overload: A Role for Vasoconstrictor Prostanoids

Plasma levels of the vasoactive substance uridine adenosine tetraphosphate (Up4A) are elevated in hypertensive patients and Up4A-induced vascular contraction is exacerbated in various arteries isolated from hypertensive animals, suggesting a potential role of Up4A in development of hypertension. We previously demonstrated that Up4A produced potent and partially endothelium-dependent relaxation in the porcine coronary microvasculature. Since pressure-overload is accompanied by structural abnormalities in the coronary microvasculature as well as by endothelial dysfunction, we hypothesized that pressure-overload blunts the coronary vasodilator response to Up4A, and that the involvement of purinergic receptors and endothelium-derived factors is altered. The effects of Up4A were investigated using wire-myography in isolated coronary small arteries from Sham-operated swine and swine with prolonged (8 weeks) pressure overload of the left ventricle induced by aortic banding (AoB). Expression of purinergic receptors and endothelium-derived factors was assessed in isolated coronary small arteries using real-time PCR. Up4A (10-9 to 10-5 M) failed to produce contraction in isolated coronary small arteries from either Sham or AoB swine, but produced relaxation in preconstricted arteries, which was significantly blunted in AoB compared to Sham. Blockade of purinergic P1, and P2 receptors attenuated Up4A-induced coronary relaxation more, while the effect of P2X1-blockade was similar and the effects of A2A- and P2Y1-blockade were reduced in AoB as compared to Sham. mRNA expression of neither A1, A2, A3, nor P2X1, P2X7, P2Y1, P2Y2, nor P2Y6-receptors was altered in AoB as compared to Sham, while P2Y12 expression was higher in AoB. eNOS inhibition attenuated Up4A-induced coronary relaxation in both Sham and AoB. Additional blockade of cyclooxygenase enhanced Up4A-induced coronary relaxation in AoB but not Sham swine, suggesting the involvement of vasoconstrictor prostanoids. In endothelium-denuded coronary small arteries from normal swine, thromboxane synthase (TxS) inhibition enhanced relaxation to Up4A compared to endothelium-intact arteries, to a similar extent as P2Y12 inhibition, while the combination inhibition of P2Y12 and TxS had no additional effect. In conclusion, Up4A-induced coronary relaxation is blunted in swine with AoB, which appears to be due to the production of a vasoconstrictor prostanoid, likely thromboxane A2.

Regulation of myocardial oxygen delivery in response to graded reductions in hematocrit: role of K+ channels.

This study was designed to identify mechanisms responsible for coronary vasodilation in response to progressive decreases in hematocrit. Isovolemic hemodilution was produced in open-chest, anesthetized swine via concurrent removal of 500ml of arterial blood and the addition of 500ml of 37°C saline or synthetic plasma expander (Hespan, 6% hetastarch in 0.9% sodium chloride). Progressive hemodilution with Hespan resulted in an increase in coronary flow from 0.39±0.05 to 1.63±0.16ml/min/g (P<0.001) as hematocrit was reduced from 32±1 to 10±1% (P<0.001). Overall, coronary flow corresponded with the level of myocardial oxygen consumption, was dependent on arterial pressures≥~60mmHg, and occurred with little/no change in coronary venous PO2. Anemic coronary vasodilation was unaffected by the inhibition of nitric oxide synthase (L-NAME: 25mg/kg iv; P=0.92) or voltage-dependent K+ (K V) channels (4-aminopyridine: 0.3mg/kg iv; P=0.52). However, administration of the K ATP channel antagonist (glibenclamide: 3.6mg/kg iv) resulted in an~40% decrease in coronary blood flow (P<0.001) as hematocrit was reduced to~10%. These reductions in coronary blood flow corresponded with significant reductions in myocardial oxygen delivery at baseline and throughout isovolemic anemia (P<0.001). These data indicate that vasodilator factors produced in response to isovolemic hemodilution converge on vascular smooth muscle glibenclamide-sensitive (K ATP) channels to maintain myocardial oxygen delivery and that this response is not dependent on endothelial-derived nitric oxide production or pathways that mediate dilation via K V channels.

The human coronary vasodilatory response to acute mental stress is mediated by neuronal nitric oxide synthase.

Mental stress-induced ischemia approximately doubles the risk of cardiac events in patients with coronary artery disease, yet the mechanisms underlying changes in coronary blood flow in response to mental stress are poorly characterized. Neuronal nitric oxide synthase (nNOS) regulates basal coronary blood flow in healthy humans and mediates mental stress-induced vasodilation in the forearm. However, its possible role in mental stress-induced increases in coronary blood flow is unknown. We studied 11 patients (6 men and 5 women, mean age: 58 ± 14 yr) undergoing elective diagnostic cardiac catheterization and assessed the vasodilator response to mental stress elicited by the Stroop color-word test. Intracoronary substance P (20 pmol/min) and isosorbide dinitrate (1 mg) were used to assess endothelium-dependent and -independent vasodilation, respectively. Coronary blood flow was estimated using intracoronary Doppler recordings and quantitative coronary angiography to measure coronary artery diameter. Mental stress increased coronary flow by 34 ± 7.0% over the preceding baseline during saline infusion (P < 0.01), and this was reduced to 26 ± 7.0% in the presence of the selective nNOS inhibitor S-methyl-l-thiocitrulline (0.625 µmol/min, P < 0.001). Mental stress increased coronary artery diameter by 6.9 ± 3.7% (P = 0.02) and 0.5 ± 2.8% (P = 0.51) in the presence of S-methyl-l-thiocitrulline. The response to substance P did not predict the response to mental stress (r2 = -0.22, P = 0.83). nNOS mediates the human coronary vasodilator response to mental stress, predominantly through actions at the level of coronary resistance vessels.NEW & NOTEWORTHY Acute mental stress induces vasodilation of the coronary microvasculature. Here, we show that this response involves neuronal nitric oxide synthase in the human coronary circulation.Listen to this article's corresponding podcast at http://ajpheart.podbean.com/e/nnos-and-coronary-flow-during-mental-stress/.

Altered purinergic signaling in uridine adenosine tetraphosphate-induced coronary relaxation in swine with metabolic derangement

We previously demonstrated that uridine adenosine tetraphosphate (Up4A) induces potent and partially endothelium-dependent relaxation in the healthy porcine coronary microvasculature. We subsequently showed that Up4A-induced porcine coronary relaxation was impaired via downregulation of P1 receptors after myocardial infarction. In view of the deleterious effect of metabolic derangement on vascular function, we hypothesized that the coronary vasodilator response to Up4A is impaired in metabolic derangement, and that the involvement of purinergic receptor subtypes and endothelium-derived vasoactive factors (EDVFs) is altered. Coronary small arteries, dissected from the apex of healthy swine and swine 6 months after induction of diabetes with streptozotocin and fed a high-fat diet, were mounted on wire myographs. Up4A (10−9–10−5 M)-induced coronary relaxation was maintained in swine with metabolic derangement compared to normal swine, despite impaired endothelium-dependent relaxation to bradykinin and despite blunted P2X7 receptor and NO-mediated vasodilator influences of Up4A. Moreover, a thromboxane-mediated vasoconstrictor influence was unmasked. In contrast, an increased Up4A-mediated vasodilator influence via P2Y1 receptors was observed, while, in response to Up4A, cytochrome P450 2C9 switched from producing vasoconstrictor to vasodilator metabolites in swine with metabolic derangement. Coronary vascular expression of A2A and P2X7 receptors as well as eNOS, as assessed with real-time PCR, was reduced in swine with metabolic derangement. In conclusion, although the overall coronary vasodilator response to Up4A was maintained in swine with metabolic derangement, the involvement of purinergic receptor subtypes and EDVF was markedly altered, revealing compensatory mechanisms among signaling pathways in Up4A-mediated coronary vasomotor influence in the early phase of metabolic derangement. Future studies are warranted to investigate the effects of severe metabolic derangement on coronary responses to Up4A.

Correlation of carotid artery reactivity with cardiovascular risk factors and coronary artery vasodilator responses in asymptomatic, healthy volunteers.

Carotid artery reactivity (CAR%), involving carotid artery diameter responses to a cold pressor test (CPT), is a noninvasive measure of conduit artery function in humans. This study examined the impact of age and cardiovascular risk factors on the CAR% and the relationship between CAR% and coronary artery vasodilator responses to the CPT. Ultrasound was used to measure resting and peak carotid artery diameters during the CPT, with CAR% being calculated as the relative change from baseline (%). We compared CAR% between young (n = 50, 24 ± 3 years) and older participants (n = 44, 61 ± 8 years), and subsequently assessed relationships between CAR% and traditional cardiovascular risk factors in 50 participants (44 ± 21 years). Subsequently, we compared left anterior descending (LAD) artery velocity (using transthoracic Doppler) with carotid artery diameter (i.e. CAR%) during the CPT (n = 33, 37 ± 17 years). A significantly larger CAR% was found in young versus older healthy participants (4.1 ± 3.7 versus 1.8 ± 2.6, P < 0.001). Participants without cardiovascular risk factors demonstrated a higher CAR% than those with at least two risk factors (2.9 ± 2.9 versus 0.5 ± 2.9, P = 0.019). Carotid artery diameter and LAD velocity increased during CPT (P < 0.001). Carotid diameter and change in velocity correlated with LAD velocity (r = 0.486 and 0.402, P < 0.004 and 0.02, respectively). Older age and cardiovascular risk factors are related to lower CAR%, while CAR% shows good correlation with coronary artery responses to the CPT. Therefore, CAR% may represent a valuable technique to assess cardiovascular risk, while CAR% seems to reflect coronary artery vasodilator function.

Chronic intermittent hypoxia accelerates coronary microcirculatory dysfunction in insulin-resistant Goto-Kakizaki rats.

Chronic intermittent hypoxia (IH) induces oxidative stress and inflammation, which impair vascular endothelial function. Long-term insulin resistance also leads to endothelial dysfunction. We determined, in vivo, whether the effects of chronic IH and insulin resistance on endothelial function augment each other. Male 12-wk-old Goto-Kakizaki (GK) and Wistar control rats were subjected to normoxia or chronic IH (90-s N2, 5% O2 at nadir, 90-s air, 20 cycles/h, 8 h/day) for 4 wk. Coronary endothelial function was assessed using microangiography with synchrotron radiation. Imaging was performed at baseline, during infusion of acetylcholine (ACh, 5 μg·kg(-1)·min(-1)) and then sodium nitroprusside (SNP, 5 μg·kg(-1)·min(-1)), after blockade of both nitric oxide (NO) synthase (NOS) with N(ω)-nitro-l-arginine methyl ester (l-NAME, 50 mg/kg) and cyclooxygenase (COX, meclofenamate, 3 mg/kg), and during subsequent ACh. In GK rats, coronary vasodilatation in response to ACh and SNP was blunted compared with Wistar rats, and responses to ACh were abolished after blockade. In Wistar rats, IH blunted the ability of ACh or SNP to increase the number of visible vessels. In GK rats exposed to IH, neither ACh nor SNP were able to increase visible vessel number or caliber, and blockade resulted in marked vasoconstriction. Our findings indicate that IH augments the deleterious effects of insulin resistance on coronary endothelial function. They appear to increase the dependence of the coronary microcirculation on NO and/or vasodilator prostanoids, and greatly blunt the residual vasodilation in response to ACh after blockade of NOS/COX, presumably mediated by endothelium-derived hyperpolarizing factors.

Preservation of Coronary Vasodilator Responses to the Nitroxyl Donor Angeli's Salt after Ischemia/Reperfusion of the Rat Isolated Heart

We previously reported that Angeli's salt (AS) simultaneously increases cardiac contractility and coronary flow (CF) in normal rat hearts. In this study, we tested the hypothesis that the cardiac contractile and vasodilator actions of AS will be preserved after myocardial ischaemia‐reperfusion (I/R). Isolated hearts from male rats were Langendorff‐perfused for 90 min (sham) or subjected to 30 min equilibration followed by 30 min global ischaemia and 30 min reperfusion. Haemodynamic responses to AS (1 nmol ‐ 10 μmol), the nitric oxide donor, diethylamine NONOate (DEA/NO, 1 nmol – 1 μmol) and the clinically used inotrope for heart failure, dobutamine (DOB, 0.1 nmol – 0.1 μmol) were determined. I/R reduced the cardiac contractile action of AS [change (Δ) in left ventricular (LV) +dP/dt (% baseline) by 10 μmol: sham 77 ± 13%, I/R‐treated hearts 17 ± 5%, p&lt;0.0001] however, I/R had no effect on the AS‐induced increase in heart rate (HR) [Δ HR (% baseline) by 10 μmol: sham 11 ± 3%, I/R‐treated hearts 14 ± 6%] or CF [Δ CF (% baseline) by 1 μmol: sham 72 ± 13%, I/R‐treated hearts 76 ± 15%]. In contrast, the DEA/NO‐induced vasodilatation was reduced by I/R [Δ CF (% baseline) by 1 μmol: sham 78 ± 12%, I/R‐treated hearts 37 ± 8%, p&lt;0.05]. I/R also significantly reduced the DOB‐induced increase in contractility [Δ LV+dP/dt (% baseline) by 10 nmol: sham 71 ± 13%, I/R‐treated hearts 22 ± 4%, p&lt;0.0001] while I/R aggravated DOB‐induced tachycardia [Δ HR (% baseline) by 0.1 μmol: sham 11 ± 4%, I/R‐treated hearts 36 ± 8%, p&lt;0.01], which increases the risk of arrhythmias. These data suggest that AS has superior coronary vasodilator capacity after I/R.

Time course of coronary vasodilator response to intravenous adenosine in humans (1071.2)

Measurement of coronary flow velocity reserve (CFVR) has proven useful in assessing coronary vasodilator potential in humans. CFVR is frequently assessed by measuring coronary vasodilator responses to intravenous infusion of adenosine. Importantly, the time course of the coronary vasodilator response to intravenous adenosine infusion has not been well documented. We retrospectively studied this time course during 39 adenosine stress tests obtained in 21 adults (6 F; age range 22‐76 yrs.). Peak coronary blood velocity (CBV) in the left anterior descending artery was assessed non‐invasively in the distal left anterior descending artery using transthoracic Doppler echocardiography before (baseline) and continuously throughout a 6‐min adenosine infusion (0.14 mg/kg/min) in all subjects. CFVR was quantified as CBV peak adenosine/CBVbaseline. Overall, adenosine infusion increased CBV in all subjects (P&lt;0.001) and peak CFVR was observed during the 4th minute in the group as a whole. However, marked variability in the timing of this response was observed. On an individual basis peak CFVR occurred during the 2nd (n=11), 3rd, (n=9), 4th (n=9,) 5th (n=7) and 6th min (n=3) of adenosine infusion. These data suggest that maximal coronary vasodilator responsiveness (i.e., CFVR) occurs variably between the 2nd and 6th minute of adenosine infusion. Based on these findings, we believe the current 6 min adenosine infusion protocol is appropriate. However, we suggest that CBV be monitored during each minute of the infusion so as to capture the true peak response in all subjects.Grant Funding Source: Supported by P01 HL096570 and UL1 TR000127

Coronary perivascular adipose tissue and K+ channel‐mediated vasodilation in lean and obese hearts (1071.4)

This investigation examined the mechanisms by which perivascular adipose tissue (PVAT) influences coronary vasodilation. Coronary arteries from lean and obese Ossabaw swine were isolated, incubated with or without 0.3 g of PVAT for 30 min and pre‐constricted with U46619 (1 μM). In arteries cleaned of PVAT, vasodilation to adenosine (0.01‐30 μM) was decreased ~25% in obese arteries. However, the presence of PVAT attenuated adenosine relaxation ~30% in both lean and obese arteries. Pre‐constriction with KCl (60 mM) abolished coronary dilation to adenosine, suggesting activation of K+ channels. Inhibition of KCa channels with penitrem A (1 μM) impaired responses to adenosine in lean (p&lt;0.001), but not obese (p=0.53), arteries. Dilation to the KCa channel agonist NS‐1619 (30 μM) was attenuated by PVAT in lean, but not obese, arteries. Inhibition of KV7 channels with linopirdine (10 μM) impaired adenosine dilation ~56% in lean arteries. Relaxation to the KV7 channel agonist L364,373 (10 μM) averaged 91 ± 5% in lean arteries vs. 55 ± 8% in obese arteries. Incubation with PVAT diminished vasodilation to L364,373 by ~22% in lean arteries, but had no effect in obese arteries. These findings indicate that while PVAT attenuates adenosine‐mediated vasodilation to a similar extent in lean and obese hearts, the contribution of KCa and KV7 channels to coronary vasodilator responses is markedly impaired in the setting of obesity.Grant Funding Source: Supported by HL117620 and HL092245

HDL-Mediated Protection of Coronary Vasodilator Response to Adenosine in the Hypercholesterolemic Swine

It is known that high-cholesterol diet impairs coronary vasodilatation in animal models of athe-rosclerosis irrespective of overt pathology. We evaluated the specific role of LDL and HDL on adenosine-elicited coronary vasodilatation after short time (10 weeks) high-cholesterol diet in pigs. Nineteen pigs on standard (C), atherogenic (HF) and alternate standard or atherogenic diet every other week (IHF) underwent left coronary angiography and flow (CFR) measurement during intracoronary adenosine injection. Total cholesterol, HDL, LDL, Apo lipoprotein A-1, IL-6, TNF-α and ICAM-1 were measured and histology of coronary samples was performed. IHF and HF show comparable intimal thickening of lesions, similar cholesterol (598.4 ± 198.2 and 633.2 ± 83.5 mg/dL) and LDL (502.6 ± 193.7 and 576.1 ± 83.2), while HDL is double in IHF group (88.3 ± 6.4 vs 46.4 ± 18.7 p < 0.0001). Vasodilation is reduced in HF (CFR = 1.6 ± 0.2, p < 0.001) as compared to C (2.6 ± 0.4), whilst it is preserved in IHF (2.7 ± 0.4). CFR and HDL values of all hypercholesterolemia cases are positively correlated (r = 0.88, p < 0.001). No relation with cytokines/cell adhesion markers is present. These findings suggest for the first time that elevation of plasma HDL level counteracts LDL related vasodilation impairment during coronary atherogenesis in swine.

Coronary artery disease and age: beyond atherosclerosis

Coronary artery disease and age: beyond atherosclerosis

Genetic variation and gender determine bradykinin type 1 receptor responses in human tissue: implications for the ACE-inhibitor-induced effects in patients with coronary artery disease

The efficacy of the ACE (angiotensin-converting enzyme) inhibitor perindopril in coronary artery disease [EUROPA (European trial on reduction of cardiac events with perindopril in stable coronary artery disease) study] is associated with the rs12050217 A/G single nucleotide polymorphism in the B1 receptor (bradykinin type 1 receptor) gene. To investigate the underlying mechanism, we examined the effect of this polymorphism on B1-receptor-mediated coronary artery dilation and peripheral blood mononuclear cell activation. Vasorelaxant responses of human coronary microarteries from subjects without coronary disease to des-Arg(9)-bradykinin and to bradykinin were studied in organ bath experiments. Des-Arg9-bradykinin responses were endothelium-dependent and exclusively mediated by B1 receptors, whereas responses to bradykinin were induced through B2 receptors (bradykinin type 2 receptors). The presence of the G allele reduced the response to 3 × 10(-8) mol/l des-Arg(9)-bradykinin by 29% [AA (n=13) compared with AG/GG (n=8); P<0.03], and tended to lower concentration-related responses (P=0.065) to this agonist, whereas the responses to bradykinin were unaffected by the rs12050217 genotype. In freshly obtained human mononuclear cells 1 μmol/l des-Arg(9)-bradykinin increased expression of the pro-inflammatory factors CXCL5 (CXC chemokine ligand 5) and IL6 (interleukin-6). These responses were not affected by genotype and exclusively occurred in blood cells from women, correlating (in the case of CXCL5) with their plasma 17β-oestradiol levels (r(2)=0.32, P=0.02; n=17). IL-1β (interleukin-1β) increased CXCL5 and IL6 expression in both genders, and this response was not associated with 17β-oestradiol levels. The gender difference in responses to B1 receptor stimulation in blood mononuclear cells implies possible gender differences in the response to ACE inhibitor therapy, which needs to be studied more comprehensively. The observed decrease in coronary vasodilator response might contribute to the impaired treatment response to perindopril of G allele carriers found in the EUROPA study.