Maximal Vasodilation Research Articles

Vascular response to acetazolamide decreases as a function of age in the arcAβ mouse model of cerebral amyloidosis

Deposition of β-amyloid along cerebral vessels is found in most patients suffering from Alzheimer's disease. The effects of cerebral amyloid angiopathy (CAA) on the function of cerebral blood vessels were analyzed applying cerebral blood volume (CBV)-based fMRI to transgenic arcAβ mice. In a cortical brain region of interest (ROI), displaying high CAA, arcAβ mice older than 16 months showed reduced response to the vasodilatory substance acetazolamide compared to age-matched wild-type animals, both with regard to rate (vascular reactivity) and extent of vasodilation (maximal vasodilation). In a subcortical ROI, displaying little CAA, no genotype-specific decrease was observed, but maximal vasodilation decreased with age in arcAβ and wild-types. These findings indicate that vascular β-amyloid deposits reduce the capacity of cerebral blood vessels to dilate upon demand, supporting the hypothesis that vascular β-amyloid contributes to hypoperfusion and neurological deficits observed in AD and CAA. High diagnostic accuracy of the combined readouts in detecting vascular dysfunction in arcAβ mice was found.

Vasoactive and antioxidant activities of plants used in Mexican traditional medicine for the treatment of cardiovascular diseases

This study demonstrated that the aqueous extracts of plants employed in Mexican traditional medicine for the treatment of cardiovascular diseases are able to modify the tone of arterial smooth muscle. Agastache mexicana (Kunth) Lint & Epling (Labiatae), Chenopodium murale L. (Chenopodiaceae), Chirantodendron pentadactylon Larreat (Sterculiaceae), Dracocephalum moldavica L. (Labiatae), Psittacanthus calyculatus G. Don (Loranthaceae), Prunus serotina ssp. capuli (Cav. ex Spreng) McVaugh (Rosaceae), and Sechium edule Sw. (Cucurbitaceae) contain secondary metabolites that promote vascular relaxation and display antioxidant activities. As expected, their antioxidant effects showed a significant correlation with the polyphenolics content. However, a lower correlation was found between the antioxidant activity and the maximum vasodilatory effect, suggesting that the vasodilatation elicited by the plant extracts could be only partly attributed to their antioxidant properties. The extract of P. calyculatus, which displayed a maximum vasorelaxant effect that was higher than that of acetylcholine, induced endothelium-dependent vasodilatation. Futhermore, the vasorelaxant response to the P. calyculatus extract was reduced after adding an inhibitor of soluble guanylate cyclase activity, providing evidence that the NO/cGMP pathway is involved. On the other hand, the extracts of Bocconia frutescens L. (Papaveraceae), Magnolia grandiflora L. (Magnoliaceae), and Solanum rostratum Dunal (Solanaceae) induced concentration-dependent contraction of rat aortic rings, suggesting that these plants have potential health benefits for the treatment of ailments such as venous insufficiency. The pharmacological activities of the extracts studied provide scientific support for their ethnomedical use.

RELATIONSHIP BETWEEN GLUCOSE METABOLISM AND ENDOTHELIAL DYSFUNCTION IN HYPERTENSIVE PATIENTS WITH METABOLIC SYNDROME: PP.34.434

Objectives: To study the possible relationship between glucose abnormalities and endothelial function, and their possible relationship with adipokine markers in patients with hypertension and metabolic syndrome (MS). Methods: We studied 28 hypertensive patients with MS, according to NCEP-ATPIII criteria. IR was estimated by HOMA index. According to OGTT (75 g), we divided into two groups: Patients with normal glucose tolerance (Fasting glucose <100 mg/dl and 2 h glucose <140 mg/dl) (NG=8 patients) and patients with abnormal glucose tolerance (9 subjects with glucose intolerance and 11 patients with type 2 diabetes). Endothelial dysfunction was evaluated by brachial artery ultrasonographic (Echo Blaster 128; transductor 7.5 MHz), endothelial dependent-vasodilatation(EDVD) was measured during reactive hyperaemia (%change in the diameter of brachial artery after 1 min of hyperaemia). Endothelial independent-vasodilatation (EIVD) was measured by the nitroglycerin (0.4 mg sublingually) administrated after at least 10 minutes of rest following reactive hyperemia. Maximum vasodilation occurs three to four minutes after administration. Adiponectin levels were measured by RIA. Results: AG patients had more insulin resistance tan subjects in NG group. Moreover, AG subjects were elderly (67,2 ± 4.5 vs 46,8 ± 5,6; p < 0.05), and lower adiponectin levels (p < 0.05). The percentages of change in EDVD and EIVD were: 19.54 ± 12.5 y 6.68 ± 5.2, respectively. In AG group (n = 20), the percentage of change in EDVD was lower (10.1 ± 6.2) than NG group (29.34 ± 15). Any relationship between insulin resistance and endothelial dysfunction was found (r = -0.12 y -0.009; P = NS, respectively). Adiponectin levels (6.64 ± 4.5 μg/ml) showed a significant relation with insulin resistance (r = 0.59; p < 0.05). We did not find any significant correlation between adiponectin and EDVD or EIVD (r = -0.01; p = NS). Conclusion: Glucose metabolism abnormalities in hypertensive patients with metabolic syndrome are related to elderly, lower adiponectin levels and lower vascular reactivity (estimated by EDVD). Although we did not find any significant association between endothelial dysfunction and insulin resistance or adiponectin levels, more studies with a larger sample of patients will be necessary to confirm these outcomes

Direct effect of mild hypothermia on the coronary vasodilation induced by an ATP-sensitive K channel opener, a nitric oxide donor and isoflurane in isolated rat hearts

Deliberate mild hypothermia (MHT) is applied for cerebroprotection after cardiopulmonary resuscitation and during cardiac surgery. MHT has been shown to alter both contractility and relaxation of blood vessels in the brain. However, the effects of MHT on drug-induced vasodilation are not fully understood. The aim of this study was to clarify the effects of MHT on the coronary vasodilation induced by cromakalim (an ATP-sensitive K channel opener), S-nitroso acetyl-penicillamine (SNAP; a nitric oxide donor), and isoflurane in isolated rat hearts. Male SD rat hearts were isolated and perfused with Krebs-Henseleit buffer. Coronary flow was measured with the coronary perfusion pressure kept at 60 mmHg, and coronary vascular resistance (CVR) was calculated. After cardiac arrest was induced by tetrodotoxin, the hearts were allocated to one of three temperature groups: 37, 34, and 31 degrees C (n = 7 for each). All groups received 0.01, 0.1, and 1.0 microM of either cromakalim or SNAP or were exposed to isoflurane at 1MAC and 2MAC. Finally, 50 mM of adenosine was administered to obtain maximal coronary vasodilation. CVR significantly increased after cardiac arrest, but did not change after the application of each temperature. Cromakalim, SNAP and isoflurane significantly decreased CVR in each temperature group. There were no significant differences in CVR among the three temperature groups with any of the test drugs. These results indicate that cromakalim-, SNAP-, and isoflurane-induced coronary vasodilation are not affected by MHT.

VIP/PACAP receptor mediation of cutaneous active vasodilation during heat stress in humans

Vasoactive intestinal peptide (VIP) is implicated in cutaneous active vasodilation in humans. VIP and the closely related pituitary adenylate cyclase activating peptide (PACAP) act through several receptor types: VIP through VPAC1 and VPAC2 receptors and PACAP through VPAC1, VPAC2, and PAC1 receptors. We examined participation of VPAC2 and/or PAC1 receptors in cutaneous vasodilation during heat stress by testing the effects of their specific blockade with PACAP6-38. PACAP6-38 dissolved in Ringer's was administered by intradermal microdialysis at one forearm site while a control site received Ringer's solution. Skin blood flow was monitored by laser-Doppler flowmetry (LDF). Blood pressure was monitored noninvasively and cutaneous vascular conductance (CVC) calculated. A 5- to 10-min baseline period was followed by approximately 70 min of PACAP6-38 (100 microM) perfusion at one site in normothermia and a 3-min period of body cooling. Whole body heating was then performed to engage cutaneous active vasodilation and was maintained until CVC had plateaued at an elevated level at all sites for 5-10 min. Finally, 58 mM sodium nitroprusside was perfused through both microdialysis sites to effect maximal vasodilation. No CVC differences were found between control and PACAP6-38-treated sites during normothermia (19 +/- 3%max untreated vs. 20 +/- 3%max, PACAP6-38 treated; P > 0.05 between sites) or cold stress (11 +/- 2%max untreated vs. 10 +/- 2%max, PACAP6-38 treated, P > 0.05 between sites). PACAP6-38 attenuated the increase in CVC during whole body heating when compared with untreated sites (59 +/- 3%max untreated vs. 46 +/- 3%max, PACAP6-38 treated, P < 0.05). We conclude that VPAC2 and/or PAC1 receptor activation is involved in cutaneous active vasodilation in humans.

VPAC2 And/Or PAC1 Receptors Interact with NOS during Heat Stress in Humans

VPAC2 and/or PAC1 receptors are implicated in cutaneous active vasodilation(AVD) during heat stress(HS). Nitric oxide(NO) from NOS also plays important roles in HS in humans. We hypothesized that NO and VPAC2/PAC1 interact in AVD during HS. We examined this interaction by testing the effects of specific blockade of these receptors with and without NOS inhibition during HS. The VPAC2/PAC1 antagonist, Pituitary Adenylate Cyclase Activating Peptide 6‐38(PACAP6‐38) and the NOS inhibitor, L‐NAME(LNM) were used. PACAP6‐38, LNM, a combination(MIX) of PACAP6‐38 and LNM, or Ringer's solution alone were perfused at 4 separate intradermal microdialysis sites. Skin blood flow(SkBF) was monitored by aser‐Doppler flowmetry and body temperature controlled with water‐perfused suits. The protocol began with a 10 minute baseline period without antagonist perfusion. This was followed by 45 minutes of PACAP6‐38, L‐NM or Mix perfusion at respective site in normothermia(Norm). Norm was followed by a 3‐minute period of whole body cooling (CS). Whole body heating was then performed to effect HS and activate AVD. After HS, 58mM sodium nitroprusside was perfused at all MD sites to effect maximal vasodilation for data normalization. No differences were found between Ringer's and PACAP6‐38, L‐NAME, or MIX sites during Norm(p&gt;0.05 among sites) or CS(p&gt;0.05 among sites). All three treated sites attenuated AVD in HS when compared to Ringer's sites(p&lt;0.05). Greater attenuation occurred at LNM and MIX sites than in PACAP6‐38 sites(p&lt;0.05); however, AVD attenuation was not different between LNM and MIX treated sites(P&gt;0.05, LNM vs MIX). We conclude that VPAC2/PAC1 receptors interact with NO during AVD. (supported by NIH Grant HL065599)

CGMP is involved in Cutaneous Vasodilation in Local Skin Warming in Humans

Nitric oxide (NO) dependent systems typically involve cGMP generation via NO activation of soluble guanylyl cyclase(sGC) as a step in vasodilation. We hypothesize that this mechanism participates in the vasodilation induced by increased local skin temperature (Tloc). We examined effects of a specific sGC inhibitor, ODQ, on increases in skin blood flow (SkBF) caused by increased Tloc. 3 intradermal microdialysis probes (MD) were inserted into forearm skin in 11 subjects. Skin blood flow was monitored by Laser‐Doppler Flowmetry (LDF). Local temperatures at the MD sites were controlled by specialized LDF probe‐holder/local‐heater units. The study began with perfusion of Ringer's at all sites, followed by 2%DMSO in Ringer's or 1mM ODQ dissolved in 2%DMSO/Ringer's at 2 separate MD sites. (Preliminary studies showed that 1mMODQ antagonized NO mediated vasodilation by sodium nitroprusside.) Ringer's was continuously perfused at the 3rd control site (CTR). In the protocol, Tloc was initially held at 34°C and then was raised to 41.5°C to cause local vasodilation. Finally, 58mM nitroprusside was perfused at all MD sites to cause maximal vasodilation for data normalization. Results: no SkBF differences were found between sites with Tloc=34°C (p&gt;0.05 between sites). SkBF rose at all sites as Tloc was increased (p&lt;0.05 vs Tloc=34C)). SkBF increase was attenuated at the ODQ treated site with Tloc=41.5°C (p&lt;0.01 vs Ringer's or 2%DMSO sites). These data suggest that sGC activation participates in the vasodilation induced by increased local skin temperature. (supported by NIH Grant HL065599)

Characterization of the Non-Invasive Assessment of the Cutaneous Microcirculation by Laser Doppler Perfusion Scanner

Microcirculatory dysfunction contributes to morbidity and mortality in vascular diseases. Here, we aimed at establishing a sensitive and valid method to measure microvascular reactivity during post-occlusive reactive hyperemia (PORH) using scanning laser Doppler perfusion imaging (LDPI) of the forearm. In a first series, LDPI was methodologically evaluated on the volar forearm of healthy volunteers (n = 10) before and after one to five minutes of upper arm occlusion. In a second series, readings were performed in 20 healthy subjects and 20 patients with coronary artery disease (CAD). Three minutes of forearm occlusion were sufficient to induce maximal vasodilation during PORH as indicated by maximal increase in perfusion unit (PU) amplitude that did not further increase after five-minute occlusion. Five-minute occlusion led to a significant prolongation of PORH with greater area under curve (AUC) suggesting longer lasting vasodilation of microvessels. The five-minute occlusion was associated with lower variability as compared with three minutes (intraindividual variability: 9-17% vs. 12-21%; interindividual variability: 13-24% vs. 14-26%). CAD patients exhibited significantly reduced amplitude (105 +/- 49 vs. 164 +/- 35 PU; p < 0.001), ratio (4.7 +/- 1.8 vs. 7.1 +/- 1.8; p < 0.001), and AUC (1656 +/- 1070 vs. 2723 +/- 864 PU x minutes; p = 0.001). Scanning LDPI is a feasible and reproducible method for non-invasive assessment of the cutaneous microcirculatory response during PORH.

Measurement of coronary flow reserve by noninvasive cardiac imaging

Myocardial blood flow (MBF) must respond to changes in metabolic conditions and oxygen requests to meet the needs of myocytes, and autoregulation plays a mayor role in the control of the coronary circulation [1–3]. It has been demonstrated that as the coronary artery progressively narrows, resting flow does not change at first, but maximal flow resulting from injection of a vasodilator decreases progressively [4, 5]. Coronary flow reserve (CFR) indicates the amount of additional blood flow that can be supplied to the heart over baseline blood flow. The absence of CFR implies maximal vasodilatation of the resistance vessels at rest and an inability to further increase MBF. Different terms are used to describe CFR. Absolute flow reserve is the ratio of blood flow during maximal hyperaemia in a stenotic artery to blood flow in the same artery at rest [6, 7]. The invasive, Doppler-based technique that measures coronary blood velocity at rest and during hyperaemia is a good example of absolute CFR measurement. Relative flow reserve is the ratio of hyperaemic flow in a stenotic artery to hyperaemic flow in a normal artery [8, 9]. Fractional flow reserve is the ratio of the maximum achievable flow in the presence of a stenosis to the theoretical maximum flow in the same artery if the artery were normal [10, 11]. This is the basis of the pressure-derived method that is the invasive method of choice to determine the significance of a coronary stenosis [12]. Several factors influence CFR measurement, such as the ability to achieve maximal coronary vasodilatation, heart rate and myocardial contractility, right atrial pressure, serial coronary stenosis, coronary resistance, and coronary collateral circulation [13]. Each of these factors has a different impact according to the method used for CFR evaluation, and therefore the various techniques are not interchangeable. While problems with each of these techniques may explain the difference, the choice of technique used is often governed by the availability of local resources, and the important practical issue may not be which method is best, but that the techniques do not provide comparable results.

R-(-)-.ALPHA.-Methylhistamine, a Histamine H3 Receptor Agonist, Induces Endothelium-Dependent Vasodilation in Rat Mesenteric Resistance Arteries

A novel histamine receptor subtype, histamine H(3) receptor, mediates inhibition of peripheral autonomic neurotransmission. The present study was designed to examine vascular effects of histamine H(3) receptor by using a selective histamine H(3) receptor agonist, R-(-)-alpha methylhistamine (alpha-methylhistamine), in rat mesenteric resistance arteries. The isolated mesenteric vascular beds were perfused with Krebs solution and perfusion pressure was measured. Active tone was produced by perfusion of Krebs solution containing 7 microM methoxamine. In preparations with intact endothelium, perfusion of alpha-methylhistamine (1-100 microM) for 1 min produced a concentration-dependent vasodilation. The maximum vasodilation at the highest concentration was approximately 45%. This vasodilation was abolished by endothelium removal and attenuated by histamine H(3) receptor antagonists, thioperamide and clobenpropit, but not by chlorpheniramine (histamine H(1) receptor antagonist) and cimetidine (histamine H(2) receptor antagonist). N(omega)-nitro-L-arginine methyl ester (L-NAME, nitric oxide (NO) synthase inhibitor), indomethacin (cyclooxygenase inhibitor) and tetraethylammonium (nonselective K(+)-channel blocker) and high KCl (30 mM) significantly inhibited alpha-methylhistamine-induced endothelium-dependent vasodilation. These findings suggest that alpha-methylhistamine induces endothelium-dependent vasodilation mainly via endothelium histamine H(3) receptors. It is also suggested that activation of histamine H(3) receptors in the endothelium releases mainly NO and partially prostaglandin I(2) and endothelium-derived hyperpolarizing factors to induce endothelium-dependent vasodilation.

The Importance of Assessment of Endothelial Function According to the Time Course of Flow-mediated Dilation of the Brachial Artery

Ultrasonography is widely used to evaluate atherosclerosis. Therefore, many ultrasound parameters exist, each with its own clinical implications. Many reports have shown that these ultrasound parameters are useful for evaluating the progression of atherosclerosis or the risk of cardiovascular disease in healthy persons and in persons with cardiovascular risk factors. Ultrasound parameters are categorized as either structural or functional parameters. Particularly in the early stage of atherosclerosis, functional parameters are useful for evaluating the risk of the further development of atherosclerosis. We have also reported that the pulsatility index of the brachial artery is related to atherothrombotic infarctions in high-risk elderly subjects. Next, we studied flow-mediated dilation (FMD) as a functional parameter in the early stage of atherosclerosis. FMD is believed to be associated with endothelial nitric oxide (NO) synthesis. Furthermore, NO has the ability to prevent progression in the early stage of atherosclerosis. Guideline for FMD measurement have already been established. FMD has been defined as the rate of brachial artery vasodilation 60 seconds after a sphygmomanometric cuff is deflated after being inflated for 5 minutes to a pressure 50 mmHg greater than the systolic blood pressure. In several prospective studies, FMD measured according to these guidelines was shown to be a predictor of cardiovascular disease. We have also already reported a cross-sectional study in which FMD of the brachial artery based on this guideline was found to be associated with diabetic retinopathy in elderly persons who had diabetes but no cardiovascular disease. However, because these guidelines are based on the results of a study of healthy young adults, it remains to be seen whether these guidelines can be applied to elderly persons or persons with cardiovascular risk factors such as diabetes, hypertension, and dyslipidemia. Furthermore, because vasodilation occurred continuously for several minutes after sphygmomanometric cuff deflation, the time course of FMD of the brachial artery must be assessed. Therefore, we evaluated the time course of flow-mediated dilation of the brachial artery with a UNEXEF18G (UNEX Corp., Nagoya, Japan), which can continuously measure brachial artery vasodilation. Vasodilation measured 60 seconds after sphygmomanometric cuff deflation on the basis of the International Brachial Artery Reactivity Task Force guidelines designated FMD60, and the maximum vasodilation obtained during continuous measurement of the brachial artery was designated MaxFMD. Furthermore, the elapsed time from sphygmomanometric cuff deflation to MaxFMD was designated peak time (PT). Using these parameters, we evaluated the relationship between the time course of flow-mediated dilation of the brachial artery and aging, diabetes, hypertension, and dyslipidemia. Regarding the effect of age-related alteration of the time course of FMD of the brachial artery, we showed in

Effect of carvedilol on coronary flow reserve in patients with hypertensive left-ventricular hypertrophy

Objective. Patients with hypertensive left-ventricular hypertrophy (LVH) have lower coronary flow reserve (CFR). Whether carvedilol can improve CFR of patients with hypertensive LVH is unknown. We aimed to investigate the effects of carvedilol on CFR in patients with hypertensive LVH. Methods. Sixty-three patients were randomly divided into two groups for treatment with carvedilol or metoprolol. The peak diastolic coronary flow velocity in the left anterior descending coronary artery at rest and at maximal vasodilation with dipyridamole infusion was recorded by transesophageal echocardiography (TEE), then CFR was calculated at baseline and at the end of 6 months of therapy. Left-ventricular mass index (LVMI) was calculated by 2-D echocardiography. Endothelium-dependent and -independent reactivity of the brachial artery was measured. Levels of plasma endothelin-1 (ET1), nitric oxide (NO) and other metabolites were monitored and analyzed before and after 6-month therapy. Results. Both blood pressure and heart rate decreased significantly in the two treatment groups after therapy (p<0.05). With carvedilol treatment, LVMI was lower (p<0.05), endothelium function of the brachial artery was higher (p<0.05), and peak diastolic coronary flow velocity at rest and at maximal vasodilation after dipyridamole infusion was significantly higher (p<0.05) than with metoprolol treatment, which led to a significantly higher CFR (p<0.05). Changes in CFR and LVMI with carvedilol treatment were inversely correlated (R2=0.474, p=0.036). With carvedilol treatment, plasma level of ET-1 was lower, but that of NO was significantly higher than with metoprolol treatment (both p<0.05). Conclusions. The CFR of patients with hypertensive LVH but not coronary artery disease could increase with 6-month carvedilol therapy.

Letter by Venetucci et al Regarding Article “Effect of High-Dose Intracoronary Adenosine Administration During Primary Percutaneous Coronary Intervention in Acute Myocardial Infarction: A Randomized Controlled Trial”

To the Editor: In a recent article published in the August edition of Circulation: Cardiovascular Interventions , Fokkema et al1 demonstrated that the intracoronary adenosine given during primary percutaneous coronary intervention does not reduce infarct size or the incidence of no reflow phenomenon. In this article, the authors argue that the dose of adenosine they used (240 μg given in 2 120-μg boluses) is sufficient to achieve maximal vasodilation, and they cite an article that suggests 16 μg as the dose sufficient to achieve maximal vasodilatation. This is certainly true for normal coronary circulation. However, we do not feel …

Endothelial dysfunction is associated with increased levels of biomarkers in essential hypertension

To assess the correlation between endothelial dysfunction and the serum levels of biomarkers of inflammation, remodelling and oxidative stress in essential hypertension, 78 treatment-naïve essential hypertensives (mean age 43 years) underwent measurement of endothelial dysfunction, using the maximal acetylcholine-induced forearm vasodilation and serum levels of adhesion molecules, selectins, chemokines, metalloproteinases, copper, zinc, selenium, vitamins, homocysteine, malondialdehyde, erythrocyte glutathione peroxidase and erythrocyte superoxide dismutase. Mean (+/-s.e.m.) maximal acetylcholine-induced vasodilation was 367+/-20%. Patients with a more impaired acetylcholine-dependent vasodilation (first tertile) had increased levels of e-selectin (P=0.009), p-selectin (P<0.001), monocyte chemotactic protein type 1 (MCP-1; P=0.012) and the tissue inhibitor of metalloproteinases type 1 (TIMP-1; P=0.044), which in turn showed significant inverse correlations with maximal endothelium-dependent vasodilation. Serum levels of selenium (P=0.012), vitamin C (P=0.038), erythrocyte glutathione peroxidase (P<0.001) and superoxide dismutase (P=0.022) activities were reduced in patients with a more impaired endothelium-dependent vasodilation. Recently diagnosed treatment-naïve essential hypertensives showed a relationship between the endothelial dysfunction, serum markers of inflammation and remodelling and levels of antioxidant substances. These could be potentially helpful markers of high risk in hypertensive patients.

Acute attenuation of glycocalyx barrier properties increases coronary blood volume independently of coronary flow reserve

Vascular endothelium is covered with an extensive mesh of glycocalyx constituents, which acts like an effective barrier up to several micrometers thick that shields the luminal surface of the vasculature from direct exposure to flowing blood. Many studies report that various enzymatic and pharmaceutical challenges are able to increase glycocalyx porosity, resulting in farther permeation of plasma macromolecules and greater access of red blood cells into glycocalyx domain. Attenuation of glycocalyx barrier properties therefore potentially increases the amount of blood that effectively occupies available microvascular volume. We tested in the present study whether attenuation of coronary glycocalyx barrier properties actually increases coronary blood volume and whether such changes would be noticeable during measurements of coronary flow reserve using adenosine. In anesthetized goats (n = 6) with cannulated left main coronary artery that were perfused under controlled pressure, coronary blood volume was measured via the indicator-dilution technique using high-molecular-weight (2,000 kDa) dextrans as plasma tracer and labeled red blood cells as red blood cell tracer. Coronary blood volume was determined at baseline and during intracoronary infusion of adenosine causing maximal vasodilation (0.2-0.6 mg.kg(-1).h(-1)) before and after intracoronary hyaluronidase treatment (170,000 units) of the glycocalyx. With an intact glycocalyx, coronary blood volume was 18.9 +/- 1.1 ml/100 g heart tissue at baseline, which increased to 26.3 +/- 2.7 ml/100 g after hyaluronidase treatment of the coronary glycocalyx. Maximal vasodilation by administration of adenosine further increased coronary blood volume to 33.9 +/- 6.8 ml/100 g, a value not different from the maximal coronary blood volume of 33.2 +/- 5.3 ml/100 g obtained by administration of adenosine in the absence of hyaluronidase treatment. Adenosine-induced increases in coronary conductance were not affected by hyaluronidase treatment. We conclude that acute attenuation of glycocalyx barrier properties increases coronary blood volume by approximately 40%, which is of similar magnitude as additional changes in coronary blood volume during subsequent maximal vasodilation with adenosine. Furthermore, maximal coronary blood volume following administration of adenosine was similar with and without prior hyaluronidase degradation of the glycocalyx, suggesting that adenosine and hyaluronidase potentially increase glycocalyx porosity to a similar extent. Hyaluronidase-mediated changes in coronary blood volume did not affect baseline and adenosine-induced increases in coronary conductance, demonstrating that measurements of coronary flow reserve are insufficient to detect impairment of coronary blood volume recruitment in conditions of damaged glycocalyx.

Sex differences in endothelin-1-mediated vasoconstrictor tone in middle-aged and older adults

The prevalence of cardiovascular disease is lower in middle-aged and older women than men. Increased endothelin-1-mediated vasoconstriction has been linked to the etiology of a number of cardiovascular diseases, including atherosclerosis, heart failure, and hypertension. It is unknown whether a sex difference in endothelin-1-mediated vasoconstrictor tone exists in middle-aged and older adults. Therefore, we tested the hypothesis that middle-aged and older men would demonstrate greater ET-1-mediated vasoconstrictor tone than age-matched women. Forearm blood flow in response to intra-arterial infusions of endothelin (ET)-1, BQ-123 (a selective ET(A) receptor antagonist), and BQ-788 (a selective ET(B) receptor antagonist) was assessed by venous occlusion plethysmography in 21 women (age: 58 + or - 1 yr; body mass index: 26.0 + or - 1.0 kg/m(2)) and 25 men (age: 57 + or - 2 yr; body mass index: 26.8 + or - 0.7 kg/m(2)). In response to BQ-123, the increase in forearm blood flow from baseline was significantly higher in the men than the women (24 + or - 5% vs. 9 + or - 5%; P < 0.05). In contrast, the increase in forearm blood flow in response to BQ-123 coinfused with BQ-788 was greater in the women than the men, such that the maximum vasodilation to dual endothelin receptor blockade was similar between men and women (approximately 25%). There was no difference in the vasoconstrictor response to ET-1 between the sexes. These results indicate that middle-aged and older men are under greater ET(A) receptor-mediated vasoconstrictor tone than age-matched women. Since the ET(A) receptor is the predominant receptor subtype in the coronary vasculature, this sex difference in vasoconstrictor tone may be a mechanism contributing to the sex difference in the prevalence of coronary heart disease in middle-aged and older adults.

Abstract 5584: Extra Domain A of Fibronectin (EDA) is Critically Involved in Collateral Artery Growth

Background Shear stress induced arterial remodeling leading to collateral artery formation (arteriogenesis) is an important protective mechanism in cardiovascular disease, redirecting blood flow around arterial stenoses. Toll Like Receptors (TLRs), part of the innate immune system, play an important role in arterial remodeling, indicating the presence of a yet unknown endogenous ligand responsible for TLR mediated arteriogenesis. Methods &amp; Results RT-PCR for endogenous TLR ligands was performed in mouse hind limb tissue after femoral artery occlusion (n=10). Hsp60 and EDA, candidate endogenous TLR-4 ligands, were significantly upregulated compared to sham operated hind limbs (EDA: occlusion 0.88 ± 0.77 versus sham 0.0096 ± 0.012 pg plasmid; HSP60: occlusion 0.0050 ± 0.0049 versus sham 0.0026 ± 0.0021 pg plasmid). To address the functional role of the increased EDA expression, EDA −/− (n=22) and corresponding wild type mice (BALB/C, n=22) were subjected to unilateral femoral artery ligation and contra lateral sham operation. Maximum hind limb perfusion restoration was assessed using fluorescent microspheres 7 days after surgery under maximal vasodilation. Perfusion restoration was significantly decreased in EDA −/− mice compared to wild type mice (EDA 22±2.6% vs. BALB/C 31±1.8% of sham operated hind limb perfusion, p=0.011), supporting a critical role of EDA during collateral artery growth. Conclusion We demonstrate that the Extra Domain A of fibronectin may be the endogenous TLR ligand critically involved in collateral development. Its expression is enhanced during collateral development while its depletion in mice attenuates perfusion restoration after acute arterial occlusion.

RhoA/ROK Pathway Related to the Mechanism of Higher Susceptibility to Spasm in RA Than in IMA

By investigating the expression and function of RhoA/Rho kinase pathway in the radial artery (RA), internal mammary artery (IMA), and great saphenous vein (GSV), this study aimed to elucidate the mechanism for a higher susceptibility of spasm in the RA and provide an effective drug candidate to prevent and treat RA spasm. RA, IMA, and GSV that would otherwise have been discarded were collected from 25 patients who underwent coronary artery bypass grafting. Eleven matched rings of RA, IMA, and GSV were used to evaluate the vasodilatory properties of 10(-7-)10(-4) mol/l of fasudil, a Rho-kinase inhibitor, by using in vitro organ chambers. Another 14 matched RA, IMA, and GSV were used to demonstrate the immunohistochemistry (IHC) of RhoA and mRNA of RhoA and Rho kinase. The maximal vasodilation of RA to fasudil was significantly greater than IMA. RhoA protein IHC staining was different in IMA, RA, and GSV (RA > GSV >IMA). The expression of RhoA and Rho kinase mRNA in the RA was significantly greater than in the IMA. The expression of RhoA/Rho kinase mRNA and protein and function in the RA were significantly stronger than in the IMA, suggesting that RhoA/Rho kinase pathway may be one mechanism by which RA is more susceptible to spasm than IMA. Rho kinase inhibitors can be effective drug candidates to prevent and treat vasospasm.

Androgenicity and venous endothelial function in post-menopausal women

Endothelial dysfunction is one of the early signs of cardiovascular damage. High androgen levels have been related to inflammatory endothelial markers in pre- and post-menopausal women. This cross-sectional study aimed at investigating whether free androgen index (FAI) [estimated by dividing total testosterone (nmol/l) by SHBG (nmol/l) x 100] is related to endothelial function during post-menopause. Twenty-six post-menopausal women were assessed with the dorsal hand vein compliance technique. Acetylcholine (Ach) and sodium nitroprusside (SNP) dose-response curves were constructed to test endothelium-dependent and independent relaxation, respectively. Mean age was 54 yr (+/-4) and median time since menopause was 6 yr (interquartile range: 3-9). Patients were stratified according to FAI levels into two groups: FAI greater than or less than the group median of 2.5. Waist-to-hip ratio (WHR) was significantly higher in the group with FAI>2.5, as well as median dose of Ach for maximal vasodilation [720 (360-3600) ng/min with FAI>2.5 vs 36 (0.36-360) ng/min with FAI<or=2.5; p=0.005]. Maximal vasodilation with SNP was similar in both groups. Positive correlations were observed between Ach doses and maximal vasodilation and FAI (r=0.473, p=0.015), waist (r=0.510, p= 0.011), and WHR (r=0.479, p=0.021). SHBG was negatively correlated with Ach doses (rs=-0.400, p=0.043). This study suggests that FAI, even within normal limits, is related to early changes in endothelial function in healthy post-menopausal women. Longitudinal studies are required to determine the clinical relevance of these findings.

Acetazolamide-Induced Vasodilation Does Not Inhibit the Visually Evoked Flow Response

Different methods are used to assess the vasodilator ability of cerebral blood vessels; however, the exact mechanism of cerebral vasodilation, induced by different stimuli, is not entirely known. Our aim was to investigate whether the potent vasodilator agent, acetazolamide (AZ), inhibits the neurovascular coupling, which also requires vasodilation. Therefore, visually evoked flow parameters were examined by transcranial Doppler in ten healthy subjects before and after AZ administration. Pulsatility index and peak systolic flow velocity changes, evoked by visual stimulus, were recorded in the posterior cerebral arteries before and after intravenous administration of 15 mg/kg AZ. Repeated-measures ANOVA did not show significant group main effect between the visually evoked relative flow velocity time courses before and after AZ provocation (P=0.43). Visual stimulation induced significant increase of relative flow velocity and decrease of pulsatility index not only before but also at the maximal effect of AZ. These results suggest that maximal cerebral vasodilation cannot be determined by the clinically accepted dose of AZ (15 mg/kg) and prove that neurovascular coupling remains preserved despite AZ-induced vasodilation. Our observation indicates independent regulation of vasodilation during neurovascular coupling, allowing the adaptation of cerebral blood flow according to neuronal activity even if other processes require significant vasodilation.