Human Coronary Microcirculation Research Articles

Electronic Cigarettes Impair Human Coronary Endothelial Function

Electronic (e‐) cigarettes are claimed—but unproven—to be less harmful than standard tobacco cigarettes, which are well known to impair coronary endothelial function and constitute a major cardiovascular risk factor. To determine whether e‐cigarettes cause impairment in human coronary endothelial function, we compared effects of tobacco cigarette smoking and e‐cigarette use to blunt the normal increase in myocardial blood flow (MBF) quantified by contrast enhanced echocardiography perfusion imaging, induced by the exercise pressor reflex (post‐handgrip forearm vascular occlusion). The exercise pressor reflex is a reproducible stimulus to endothelial‐dependent coronary vasodilation while also increasing coronary sympathetic vasoconstrictor drive. The coronary endothelial function testing was performed in healthy young adult cigarette smokers (n=5) and age‐matched e‐cigarette users (n=8), ages 21–38 years: a) after overnight smoking/vaping abstinence; and b) immediately after smoking one Camel‐filtered cigarette or one standard use (15 puffs in 7 minutes) of a popular tank‐style e‐cigarette (Evod: battery 3.7 volts, nicotine content 18 mg). During tobacco abstinence in the young cigarette smokers, the exercise pressor reflex increased mean arterial pressure (MAP) by 21.6 ± 4 mmHg (mean ± SE) and increased MBF by 66 ± 20% over baseline (p<0.05), the latter indicating endothelial‐dependent vasodilation in the human coronary microcirculation. As expected, the MBF failed to increase when the exercise pressor reflex was elicited immediately after cigarette smoking (Δ MBF −2 ± 24%, p=n.s.), indicating acute impairment in coronary endothelial function. The surprising new findings of this study are that MBF also failed to increase and tended to decrease by −45 ± 20% (p=n.s.) when the exercise pressor reflex was elicited immediately after acute e‐cigarette use and by −16 ± 10% (p=n.s.) even when elicited during vaping abstinence (despite comparable mean reflex increases in MAP of 21.1 and 21.6 mm Hg, respectively). Thus, our data to date suggest that, in contrast to what has been widely assumed, e‐cigarette use in young adults causes an impairment in coronary endothelial function that appears to be more persistent than with traditional tobacco cigarettes. Further research is warranted to determine if specific oxidant nanoparticles in e‐cigarette vapor mediate the impaired coronary endothelial function.Support or Funding InformationFunded by Tobacco Related Disease Research Program; ClinicalTrials.gov NCT02612701This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Acute Effect of Hookah Smoking on the Human Coronary Microcirculation

Hookah (water pipe) smoking is a major new understudied epidemic affecting youth. Because burning charcoal is used to heat the tobacco product, hookah smoke delivers not only nicotine but also large amounts of charcoal combustion products, including carbon-rich nanoparticles that constitute putative coronary vasoconstrictor stimuli and carbon monoxide, a known coronary vasodilator. We used myocardial contrast echocardiography perfusion imaging with intravenous lipid shelled microbubbles in young adult hookah smokers to determine the net effect of smoking hookah on myocardial blood flow. In 9hookah smokers (age 27 ± 5years, mean ± SD), we measured myocardial blood flow velocity (β), myocardial blood volume (A), myocardial blood flow (A× β) as well as myocardial oxygen consumption (MVO2) before and immediately after 30minutes of ad lib hookah smoking. Myocardial blood flow did not decrease with hookah smoking but rather increased acutely (88 ± 10 to 120 ± 19 a.u./s, mean ± SE, p=0.02), matching a mild increase in MVO2 (6.5 ± 0.3 to 7.6 ± 0.4ml·minute(-1), p <0.001). This was manifested primarily by increased myocardial blood flow velocity (0.7 ± 0.1 to 0.9 ± 0.1second(-1), p=0.01) with unchanged myocardial blood volume (133 ± 7 to 137 ± 7 a.u., p=ns), the same pattern of coronary microvascular response seen with a low-dose β-adrenergic agonist. Indeed, with hookah, the increased MVO2 was accompanied by decreased heart rate variability, an indirect index of adrenergic overactivity, and eliminated by β-adrenergic blockade (i.v. propranolol). In conclusion, nanoparticle-enriched hookah smoke either is not an acute coronary vasoconstrictor stimulus or its vasoconstrictor effect is too weak to overcome the physiologic dilation of coronary microvessels matching mild cardiac β-adrenergic stimulation.

Endothelium-Derived Hyperpolarization and Coronary Vasodilation: Diverse and Integrated Roles of Epoxyeicosatrienoic Acids, Hydrogen Peroxide, and Gap Junctions.

Myocardial perfusion and coronary vascular resistance are regulated by signaling metabolites released from the local myocardium that act either directly on the VSMC or indirectly via stimulation of the endothelium. A prominent mechanism of vasodilation is EDH of the arteriolar smooth muscle, with EETs and H(2)O(2) playing important roles in EDH in the coronary microcirculation. In some cases, EETs and H(2)O(2) are released as transferable hyperpolarizing factors (EDHFs) that act directly on the VSMCs. By contrast, EETs and H(2)O(2) can also promote endothelial KCa activity secondary to the amplification of extracellular Ca(2+) influx and Ca(2+) mobilization from intracellular stores, respectively. The resulting endothelial hyperpolarization may subsequently conduct to the media via myoendothelial gap junctions or potentially lead to the release of a chemically distinct factor(s). Furthermore, in human isolated coronary arterioles dilator signaling involving EETs and H(2)O(2) may be integrated, being either complimentary or inhibitory depending on the stimulus. With an emphasis on the human coronary microcirculation, this review addresses the diverse and integrated mechanisms by which EETs and H(2)O(2) regulate vessel tone and also examines the hypothesis that myoendothelial microdomain signaling facilitates EDH activity in the human heart.

Cocaine-Induced Vasoconstriction in the Human Coronary Microcirculation

Background— Cocaine is a major cause of acute coronary syndrome, especially in young adults; however, the mechanistic underpinning of cocaine-induced acute coronary syndrome remains limited. Previous studies in animals and in patients undergoing cardiac catheterization suggest that cocaine constricts coronary microvessels, yet direct evidence is lacking. Methods and Results— We used myocardial contrast echocardiography to test the hypothesis that cocaine causes vasoconstriction in the human coronary microcirculation. Measurements were performed at baseline and after a low, nonintoxicating dose of intranasal cocaine (2 mg/kg) in 10 healthy cocaine-naïve young men (median age, 32 years). Postdestruction time-intensity myocardial contrast echocardiography kinetic data were fit to the equation y=A(1−e −βt ) to quantify functional capillary blood volume (A), microvascular flow velocity (β), and myocardial perfusion (A×β). Heart rate, mean arterial pressure, and left ventricular work (2-dimensional echocardiography) were measured before and 45 minutes after cocaine. Cocaine increased mean arterial pressure (by 14±2 mm Hg [mean±SE]), heart rate (by 8±3 bpm), and left ventricular work (by 50±18 mm Hg·mL −1 ·bpm −1 ). Despite the increases in these determinants of myocardial oxygen demand, myocardial perfusion decreased by 30% (103.7±9.8 to 75.9±10.8 arbitrary units [AU]/s; P &lt;0.01) mainly as a result of decreased capillary blood volume (133.9±5.1 to 111.7±7.7 AU; P &lt;0.05) with no significant change in microvascular flow velocity (0.8±0.1 to 0.7±0.1 AU). Conclusions— In healthy cocaine-naïve young adults, a low-dose cocaine challenge evokes a sizeable decrease in myocardial perfusion. Moreover, the predominant effect is to decrease myocardial capillary blood volume rather than microvascular flow velocity, suggesting a specific action of cocaine to constrict terminal feed arteries.

Diversity in Mechanisms of Endothelium‐Dependent Vasodilation in Health and Disease

Small arterioles (40-150μm) contribute to the majority of vascular resistance within organs and tissues. Under resting conditions, the basal tone of these vessels is determined by a delicate balance between vasodilator and vasoconstrictor influences. Cardiovascular homeostasis and regional tissue perfusion is largely a function of the ability of these small blood vessels to constrict or dilate in response to the changing metabolic demands of specific tissues. The endothelial cell layer of these microvessels is a key modulator of vasodilation through the synthesis and release of vasoactive substances. Beyond their vasomotor properties, these compounds importantly modulate vascular cell proliferation, inflammation, and thrombosis. Thus, the balance between local regulation of vascular tone and vascular pathophysiology can vary depending upon which factors are released from the endothelium. This review will focus on the dynamic nature of the endothelial released dilator factors depending on species, anatomic site, and presence of disease, with a focus on the human coronary microcirculation. Knowledge how endothelial signaling changes with disease may provide insights into the early stages of developing vascular inflammation and atherosclerosis, or related vascular pathologies.

Regulation of the human coronary microcirculation

Atherosclerosis of conduit epicardial arteries is the principal culprit behind the complications of coronary heart disease, but a growing body of literature indicates that the coronary microcirculation also contributes substantially to the pathophysiology of cardiovascular disease. An understanding of mechanisms regulating microvascular function in humans is an essential foundation for understanding the role in disease, especially since these regulatory mechanisms vary substantially across species and vascular beds. In fact all subjects whose coronary tissue was used in the studies described have medical conditions that warrant cardiac surgery, thus relevance to the normal human must be inferential and is based on tissue from subjects without known arteriosclerotic disease. This review will focus on recent advances in the physiological and pathological mechanisms of coronary microcirculatory control, describing a robust plasticity in maintaining endothelial control over dilation, including mechanisms that are most relevant to the human heart. This article is part of a Special Issue entitled "Coronary Blood Flow".

Endothelin-1-induced contractile responses of human coronary arterioles via endothelin-A receptors and PKC-α signaling pathways

We investigated the contractile function in responses to endothelin-1 (ET-1) in the human coronary microvasculature as well as the roles of endothelin receptors and protein kinase C-alpha (PKC-alpha) in these responses. Human atrial tissue was harvested from patients who underwent cardiac surgery pre- and post-cardioplegia (CP)/cardiopulmanory bypass (CPB). Microvascular constriction was assessed in pre- and post-CP/CPB samples in responses to ET-1, in the presence and absence of an endothelin-A (ET-A) receptor antagonist, an endothelin-B (ET-B) receptor antagonist, or a PKC-alpha inhibitor, respectively. The expression and localization of the ET-A and ET-B receptors were also examined using immunoblot and immunofluorescence photomicroscopy. The post-CP/CPB contractile response of coronary arterioles to ET-1 was significantly decreased compared with the pre-CP/CPB responses. The response to ET-1 was significantly inhibited in the presence of the ET-A antagonist BQ123 (10(-7)mol/L), but these values remained unchanged with the ET-B receptor antagonist BQ788 (10(-7)mol/L). Pretreatment with the PKC-alpha inhibitor safingol (2.5 x 10(-5) mol/L) reversed the ET-1 responses from contraction into relaxation. The total polypeptide levels of ET-A and ET-B receptors were not altered post-CP/CPB. Immunoblot and immunofluorescent staining displayed strong signals for ET-A receptors and relatively weak signals for ET-B receptors localized on coronary microvasculature. CP/CPB decreases the contractile function of human coronary microvessels in responses to ET-1. ET-A receptors are predominantly localized in the human coronary microcirculation, whereas ET-B receptors seem to be less abundant. The contractile response to ET-1 is in part through the activation of ET-A receptors and PKC-alpha. These results suggest a role of ET-1-induced contraction in the vasomotor dysfunction after cardiac surgery.

Vascular control in humans: focus on the coronary microcirculation

Myocardial perfusion is regulated by a variety of factors that influence arteriolar vasomotor tone. An understanding of the physiological and pathophysiological factors that modulate coronary blood flow provides the basis for the judicious use of medications for the treatment of patients with coronary artery disease. Vasomotor properties of the coronary circulation vary among species. This review highlights the results of recent studies that examine the mechanisms by which the human coronary microcirculation is regulated in normal and disease states, focusing on diabetes. Multiple pathways responsible for myogenic constriction and flow-mediated dilation in human coronary arterioles are addressed. The important role of endothelium-derived hyperpolarizing factors, their interactions in mediating dilation, as well as speculation regarding the clinical significance are emphasized. Unique properties of coronary arterioles in human vs. other species are discussed.

2008 George E. Brown Memorial Lecture—Flow-Induced Vasodilation in the Human Heart: Unique Endothelial Mechanisms and Clinical Insights

The most physiologically important stimulus for endothelium-dependent dilation is shear stress. Flow across the endothelial surface triggers a mechanochemical signal transduction pathway that results in release of nitric oxide (NO), prostacyclin, and/or endothelial-derived hyperpolarizing factors (EDHFs) such as hydrogen peroxide (H 2 O 2 ) and epoxyeicosatrienoic acid (EET). In most normal arteries, NO is the prominent mediator; however, in disease states, NO may be quenched by an elevation in superoxide. In these situations, compensatory dilator mechanisms may emerge, using EDHFs. One mechanism of this compensation may involve an important dilator pathway interaction whereby NO inhibits CYP450 monooxygenase. This is particularly prominent in the microcirculation, where disease-induced loss of NO often results in enhanced endothelial CYP450 activity and generation of EET as an alternate dilator. Recent data indicate that H 2 O 2 can also inhibit CYP450. In the human coronary microcirculation from subjects with coronary artery disease, NO and prostacyclin play little role in the dilation to most pharmacological agonists or to shear stress. Instead, EETs and H 2 O 2 are critical mediators of flow-induced dilation. Interestingly, the dilation requires ROS generation from the endothelial mitochondrial electron transport chain. Dual vessel bioassay studies suggest that H 2 O 2 is the transferable compound responsible for hyperpolarizing and relaxing the underlying vascular smooth muscle cells. In contrast, dilation to bradykinin also involves both H 2 O 2 and EET, but the H 2 O 2 originates from endothelial nicotinamide adenine dinucleotide phosphateoxidase oxidase, and EETs serve as an important transferable dilator agent. Endothelial release of NO, EET, and H 2 O 2 has implications beyond vasodilation. NO and EETs have potent antiatherosclerotic properties. Hydrogen peroxide, on the other hand, although a potent dilator, has proatherogenic properties. Therefore, it is hypothesized that the profile of endothelial factors released by shear stress and other stimuli may help determine the balance between proatherosclerotic and anti-atherosclerotic factors in vascular homeostasis.

Endothelial cytoskeletal elements are critical for flow-mediated dilation in human coronary arterioles.

Mitochondrial H2O2 contributes to flow-mediated dilation (FMD) in human coronary arterioles (HCA). We examined the hypothesis that the endothelial cytoskeleton plays a critical role in transducing endothelial wall shear stress into a stimulus for releasing mitochondrial ROS. Phallacidin together with alpha-, beta-tubulin antibodies and Mito-Tracker Red showed the proximity of F-actin, microtubules and mitochondria in endothelial cells. Cytochalasin D (CytoD) and nocodazole (Noc) disrupted endothelial F-actin and microtubules in HCA, respectively, concurrent with a reduction in the generation of cytosolic and H2O2 (hydroethidine and dichlorodihydrofluorescein fluorescence) and mitochondrial superoxide (mitoSox) during flow (control: 3.5 +/- 1.6, Cyto D: 0.51 +/- 0.2, Noc: 0.81 +/- 0.6). FMD, but not the dilation to bradykinin or papaverine, was reduced by Cyto D (26 +/- 10% vs. 56 +/- 3%) or Noc (26 +/- 11% vs. 58 +/- 7%). These results suggest that cytoskeletal elements are a critical component of the signaling mechanism linking endothelial shear stress and mitochondrial release of ROS in the human coronary microcirculation.

12‐ and 15‐hydroxyeicosatetraenoic acids may function as endothelium‐derived hyperpolarizing factors in the human coronary microcirculation

12‐ and 15‐hydroxyeicosatetraenoic acids (12‐ and 15‐HETEs) are 12/15‐lipoxygenase metabolites of arachidonic acid (AA) that exhibit vasodilator activity characteristic of endothelium‐derived hyperpolarizing factors (EDHFs) in some animals. EDHFs predominate in microvessels, particularly in cardiovascular disease; however, a role for HETEs in human coronary arterioles (HCAs) has not been explored. We hypothesized that HCAs produce HETEs and that these lipids elicit vasodilation. HCAs (diameter 100–200 ìm) were isolated from right atrial appendages (n=13) and 14C‐AA metabolism was assayed by HPLC. HETE formation was quantified by mass spectrometry. Diameter changes of pressurized HCAs were measured by videomicroscopy. As observed by HPLC, HCAs metabolized 14C‐AA primarily to two products that coeluted with authentic 12‐ and 15‐HETE. Mass spectrometry confirmed the structures and revealed endogenous release of these lipids into perfusate (4.9±2.2 and 8.7±5.2 pg/min, respectively, n=6). Furthermore, 12‐ and 15‐HETE each induced a concentration‐dependent dilation (81±5% and 72±6% at 10−5 M, respectively, n=5 each) that was abolished by 40 mM KCl (6±5% and −2±3%, respectively, n=3 each, p&lt;0.05). We conclude that 12‐ and 15‐HETE are endogenously produced in HCAs and that they elicit dilation by a mechanism requiring K+ channels. These findings support a role for these lipids as EDHFs in the human heart.

Hydrogen Peroxide Inhibits Cytochrome P450 Epoxygenases

The cytochrome P450 epoxygenase (CYP)-derived metabolites of arachidonic acid the epoxyeicosatrienoic acids (EETs) and hydrogen peroxide (H2O2) both function as endothelium-derived hyperpolarizing factors (EDHFs) in the human coronary microcirculation. However, the relative importance of and potential interactions between these 2 vasodilators remain unexplored. We identified a novel inhibitory interaction between CYPs and H2O2 in human coronary arterioles, where EDHF-mediated vasodilatory mechanisms are prominent. Bradykinin induced vascular superoxide and H2O2 production in an endothelium-dependent manner and elicited a concentration-dependent dilation that was reduced by catalase but not by 14,15-epoxyeicosa-5(Z)-enoic acid (EEZE), 6-(2-propargyloxyphenyl)hexanoic acid, sulfaphenazole, or iberiotoxin. However, in the presence of catalase, an inhibitory effect of these compounds was unmasked. In a tandem-bioassay preparation, application of bradykinin to endothelium-intact donor vessels elicited dilation of downstream endothelium-denuded detectors that was partially inhibited by donor-applied catalase but not by detector-applied EEZE; however, EEZE significantly inhibited dilation in the presence of catalase. EET production by human recombinant CYP 2C9 and 2J2, 2 major epoxygenase isozymes expressed in human coronary arterioles, was directly inhibited in a concentration-dependent fashion by H2O2 in vitro, as observed by high-performance liquid chromatography (HPLC); however, EETs were not directly sensitive to oxidative modification. H2O2 inhibited dilation to arachidonic acid but not to 11,12-EET. These findings suggest that an inhibitory interaction exists between 2 EDHFs in the human coronary microcirculation. CYP epoxygenases are directly inhibited by H2O2, and this interaction may modulate vascular EET bioavailability.

Protein kinase C alpha modulates microvascular reactivity in the human coronary and skeletal microcirculation

Cardioplegic arrest (CP) and cardiopulmonary bypass (CPB) can lead to dysfunction in the coronary and skeletal microcirculation leading to impaired tissue perfusion. alpha-Adrenergic signaling pathways acting on these microcirculatory beds are thought to involve protein kinase C (PKC). We investigate here the role of the conventional PKCs in microvascular function in the setting of CP/CPB. Atrial and skeletal muscle was harvested from 30 patients undergoing cardiac surgery before and after CP/CPB. Microvessels were used for Western blotting and immunofluorescent staining against conventional PKCs. Microvascular constriction was assessed in pre- and post-CP/CPB samples in response to alpha-adrenergic stimulation with phenylephrine, with and without a PKC-alpha inhibitor or PKC-alpha activator. PKC activity was assessed in isolated microvessels. Western blotting and immunostaining demonstrated only PKC-alpha in coronary and skeletal microvessels. CP/CPB diminished contractile responses to phenylephrine in coronary and skeletal samples. Inhibition of PKC-alpha reduced phenylephrine induced vasoconstriction in coronary and skeletal microvessels, whereas activation of PKC-alpha-augmented phenylephrine induced responses. PKC activity was decreased in coronary microvessels and to an even greater degree in skeletal microvessels after CP/CPB. PKC-alpha is the predominant conventional PKC present in the human coronary and skeletal microcirculation. It likely plays a key role in alpha-adrenergic signaling in microvessels and in the vasomotor dysfunction after CP/CPB.

Epoxyeicosatrienoic and dihydroxyeicosatrienoic acids dilate human coronary arterioles via BKCachannels: implications for soluble epoxide hydrolase inhibition

Epoxyeicosatrienoic acids (EETs) are metabolized by soluble epoxide hydrolase (sEH) to form dihydroxyeicosatrienoic acids (DHETs) and are putative endothelium-derived hyperpolarizing factors (EDHFs). EDHFs modulate microvascular tone; however, the chemical identity of EDHF in the human coronary microcirculation is not known. We examined the capacity of EETs, DHETs, and sEH inhibition to affect vasomotor tone in isolated human coronary arterioles (HCAs). HCAs from right atrial appendages were prepared for videomicroscopy and immunohistochemistry. In vessels preconstricted with endothelin-1, three EET regioisomers (8,9-, 11,12-, and 14,15-EET) each induced a concentration-dependent dilation that was sensitive to blockade of large-conductance Ca2+-activated K+ (BK(Ca)) channels by iberiotoxin. EET-induced dilation was not altered by endothelial denudation. 8,9-, 11,12-, and 14,15-DHET also dilated HCA via activation of BK(Ca) channels. Dilation was less with 8,9- and 14,15-DHET but was similar with 11,12-DHET, compared with the corresponding EETs. Immunohistochemistry revealed prominent expression of cytochrome P-450 (CYP450) 2C8, 2C9, and 2J2, enzymes that may produce EETs, as well as sEH, in HCA. Inhibition of sEH by 1-cyclohexyl-3-dodecylurea (CDU) enhanced dilation caused by 14,15-EET but reduced dilation observed with 11,12-EET. DHET production from exogenous EETs was reduced in vessels pretreated with CDU compared with control, as measured by liquid chromatography electrospray-ionization mass spectrometry. In conclusion, EETs and DHETs dilate HCA by activating BK(Ca) channels, supporting a role for EETs/DHETs as EDHFs in the human heart. CYP450s and sEH may be endogenous sources of these compounds, and sEH inhibition has the potential to alter myocardial perfusion, depending on which EETs are produced endogenously.

Flow-induced dilation of human coronary arterioles: important role of Ca(2+)-activated K(+) channels.

Flow-induced vasodilation (FID) is a physiological mechanism for regulating coronary flow and is mediated largely by nitric oxide (NO) in animals. Because hyperpolarizing mechanisms may play a greater role than NO in the microcirculation, we hypothesized that hyperpolarization contributes importantly to FID of human coronary arterioles. Arterioles from atria or ventricles were cannulated for videomicroscopy. Membrane potential of vascular smooth muscle cells (VSMCs) was measured simultaneously. After constriction with endothelin-1, increases in flow induced an endothelium-dependent vasodilation. Nomega-Nitro-L-arginine methyl ester 10(-4) mol/L modestly impaired FID of arterioles from patients without coronary artery disease (CAD), whereas no inhibition was seen in arterioles from patients with CAD. Indomethacin 10(-5) mol/L was without effect, but 40 mmol/L KCl attenuated maximal FID. Tetraethylammonium 10(-3) mol/L but not glibenclamide 10(-6) mol/L reduced FID. Charybdotoxin 10(-8) mol/L impaired both FID (15+/-3% versus 75+/-12%, P<0.05) and hyperpolarization (-32+/-2 mV [from -28+/-2 mV after endothelin-1] versus -42+/-2 mV [-27+/-2 mV], P<0.05). Miconazole 10(-6) mol/L or 17-octadecynoic acid 10(-5) mol/L reduced FID. By multivariate analysis, age was an independent predictor for the reduced FID. Conclusions-We conclude that shear stress induces endothelium-dependent vasodilation, hyperpolarizing VSMCs through opening Ca(2+)-activated K(+) channels in human coronary arterioles. In subjects without CAD, NO contributes to FID. NO and prostaglandins play no role in patients with CAD; rather, cytochrome P450 metabolites are involved. This is consistent with a role for endothelium-derived hyperpolarizing factor in FID of the human coronary microcirculation.

Pharmacologic activation of the human coronary microcirculation in vitro: endothelium-dependent dilation and differential responses to acetylcholine.

In vivo studies of the human coronary resistance circulation cannot control for indirect effects of myocardial metabolism, compression, and neurohumoral influences. This study directly examined the vasodilator responses of the human coronary microcirculation to both receptor-dependent and -independent agonists. Atrial arterioles were dissected from human right atrial appendage (103 +/- 2 microns diameter, n = 185 vessels from 145 patients) obtained at the time of cardiopulmonary bypass and left ventricular vessels from explanted human hearts (148 +/- 10 microns diameter, n = 57 vessels from 18 patients). After dissection, vessels were mounted onto pipettes in Kreb's buffer under conditions of zero flow and at a constant distending pressure of 60 mmHg. Drugs were applied extraluminally and steady state changes in diameter measured with videomicroscopy. After contraction by endothelin or spontaneous tone, increasing concentrations of adenosine diphosphate (ADP) produced a similar dose-dependent dilation in vessels from atria (maximum 89 +/- 4%, n = 76) and ventricles (maximum 74 +/- 9%, n = 10). The dilation to ADP was abolished by mechanical removal of the endothelium. Similar dilator responses were found to bradykinin, substance P, arachidonic acid, and the calcium ionophore A23187 in both atria and ventricle. In contrast, acetylcholine (ACh) constricted all atrial vessels (-58 +/- 3%, n = 63) regardless of patient age or underlying disease. This constriction was attenuated by denudation, but not affected by inhibition of nitric oxide synthase or cyclo-oxygenase. Microvessels isolated from human ventricle exhibited a heterogeneous response to ACh with dilation being the predominant response. We conclude that isolated human coronary arterioles demonstrate endothelium-dependent dilation. However, the response to acetylcholine is unique with vasoconstriction in atrial vessels and dilation in ventricular arterioles.

Myogenic constriction of human coronary arterioles.

Myogenic constriction is an important mechanism of blood flow regulation; however, it has never been demonstrated in the human coronary circulation. We examined responses of human coronary resistance vessels in vitro to changes in intraluminal pressure and evaluated the role of protein kinase C (PKC). Microvessels (passive diameter 44-227 microns) were dissected from atrial appendages obtained during cardiac surgery and studied under conditions of zero flow. In response to stepped increases in pressure, there was a graded response such that at 100 mmHg, vessels constricted to 55 +/- 4% of their passive diameter. There was an inverse relationship between vessel diameter and myogenic responsiveness. Basal tone was attenuated by inhibition of voltage-dependent calcium channels (VDCC) with diltiazem and by inhibition of PKC with calphostin C. Activation of PKC with phorbol 12-myristate 13-acetate (PMA) enhanced basal tone. Active myogenic constriction was also impaired by calphostin C and augmented by PMA. Arterioles from patients with hypertension demonstrated enhanced myogenic constriction compared with vessels from normotensive patients (0.55 +/- 0.04 vs. 0.74 +/- 0.03; P < 0.01). These results demonstrate myogenic constriction in the human coronary microcirculation. Regulation of extracellular calcium by VDCC and intracellular calcium by PKC are important in mediating the magnitude of basal tone and myogenic responsiveness of these vessels.

Endothelial dysfunction of the coronary microvasculature is associated with coronary blood flow regulation in patients with early atherosclerosis.

The vascular endothelium is capable of regulating tissue perfusion by the release of endothelium-derived relaxing factor to modulate vasomotor tone of the resistance vasculature. To test whether atherosclerosis is associated with a functional abnormality of endothelium-mediated microvascular relaxation affecting coronary blood flow regulation, we compared coronary blood flow responses with cold pressor testing with the response of the coronary vasculature to acetylcholine (an endothelium-dependent vasodilator) and to papaverin (a direct dilator of vascular smooth muscle) in 12 normal control patients and in 19 patients with non-flow-limiting epicardial atherosclerosis (CAD). The drugs were subselectively infused into the left anterior descending coronary artery via a Doppler catheter, and the response in coronary blood flow was assessed by measuring intracoronary blood flow velocity and cross-sectional arterial area (quantitative angiography). Coronary vascular resistance decreased in all normal control patients by -24.1 +/- 5.5% (mean +/- SD) during the cold pressor test, whereas the CAD patients demonstrated a variable coronary vascular resistance response to cold pressor testing despite comparable changes in the rate-pressure product. The slopes of the acetylcholine dose-blood flow response (percent change in coronary blood flow/dosage of acetylcholine) were significantly reduced in the CAD patients with 38.5 +/- 24.8 compared with the normal patients (80.8 +/- 28.1; p less than 0.001). Although coronary blood flow responses to papaverin were slightly but significantly (p less than 0.05) reduced in the CAD patients, the response to the endothelium-dependent dilator acetylcholine was considerably out of proportion to the papaverin response in these patients compared with the normal patients. The capacity of the coronary system to increase blood flow in response to acetylcholine expressed as relative proportion of the maximal papaverin response was 52.5 +/- 18.2% in the normal control patients but only 33.6 +/- 23.6% in the CAD patients (p less than 0.025 versus normals). There was a significant negative correlation (r = -0.69; p less than 0.0001) between cold pressor test-induced changes in coronary vascular resistance and the capacity of the coronary system to increase blood flow in response to acetylcholine. Early stages of epicardial atherosclerosis are associated with an impairment in endothelium-dependent dilation of the coronary microvasculature, indicating that the pathophysiological consequences of atherosclerosis may extend into the human coronary microcirculation. The correlation between cold pressor test-induced coronary vascular resistance changes and the extent of endothelial dysfunction suggests a relation between endothelial function of the microvasculature and coronary blood flow regulation during sympathetic stimulation associated with increased myocardial work.