Human Coronary Artery Segments Research Articles

Expression of Heregulin in Human Coronary Atherosclerotic Lesions

Background: Endothelial cells, monocytes/macrophages, and vascular smooth muscle cells contribute to the establishment and progression of atherosclerotic lesions by expressing growth and inflammatory factors. The aim of the present study was to determine whether heregulin (HRG) is associated with human coronary artery disease. Methods: Twenty-six fresh human coronary artery segments were collected at autopsy. Expression of cysteine-rich 61 (CYR61) and VEGF in response to HRG was studied in the human endothelial cell line EA.hy926, and expression of CYR61 and HRG was evaluated in activated macrophages isolated from peripheral blood of healthy donors. Results: We found that HRG was overexpressed at the protein and mRNA level in all lesions analyzed and gradually increased as the stages of the lesions progressed. Expression of HRG was observed in the intima primarily in macrophages. The same specimens were analyzed for the expression of CYR61, an angiogenetic factor regulated by HRG in breast cancer epithelial cells. CYR61 was expressed in both normal and atheromatic specimens, but its expression was significantly enhanced in macrophages of the intima. Activation of primary human macrophages results in increased expression of both HRG and CYR61. In addition, studies in endothelial cells where no endogenous HRG is present showed that HRG induces expression of CYR61 and secretion of VEGF. Conclusions: HRG may, therefore, play an important role in the development of coronary artery disease and the expansion of the atherosclerotic plaque and may locally regulate the expression of the angiogenetic factor CYR61.

αvβ3‐Targeted detection of arteriopathy in transplanted human coronary arteries: an autoradiographic study

Graft arteriopathy (GA), characterized by diffuse concentric narrowing of coronary arteries, is the major cause of late graft failure in cardiac transplantation. alphavbeta3 Integrin is up-regulated in proliferating vascular cells and may constitute an appropriate target for imaging GA. We used a human/mouse chimeric model of GA, in which segments of human coronary artery were transplanted to severe combined immunodeficiency mice, followed by reconstitution with allogeneic human peripheral blood mononuclear cells (PBMC). This led to vascular remodeling characterized by neointima formation over a period of 4 wk. alphavbeta3 expression in the graft was minimal in animals without PBMC, considerably increased by 2 wk, and decreased toward baseline by 4 wk after PBMC reconstitution. Cell proliferation was maximal at 2 wk, correlating with peak alphavbeta3 expression. RP748, an 111In-labeled alphavbeta3 (active conformation)-targeted radiotracer was injected into groups of 5 recipients at 0, 2, and 4 wk after PBMC reconstitution. Relative uptakes, defined as autoradiographic intensity in the graft/native aortas closely tracked the proliferative process. Specificity of uptake was demonstrated using excess nonlabeled tracer. In conclusion, alphavbeta3 integrin is transiently up-regulated (and activated) in GA and may be targeted by RP748 for detection of the proliferative process in early GA.

Protein and mRNA expression levels of VEGF-A and TGF-β1 in different types of human coronary atherosclerotic lesions

It is well documented that inflammation plays a major role in the establishment and progression of atherosclerosis. Endothelial cells, vascular smooth muscle cells and monocytes/macrophages are involved in this process by expressing inflammatory factors. The aim of the present study was to evaluate potential association and risk of VEGF-A and TGF-beta1 in human coronary atherosclerotic lesions. Twenty-six fresh human coronary artery segments were collected at autopsy. Conventional histology was performed and samples were classified into: no lesion group (NL), fatty streak group (FS), plaque group (P) and complicated lesion group (CL) based on the atherosclerotic lesion type. RNA extraction-analysis with RT-PCR and immunohistochemistry was also performed. We observed that VEGF-A protein and mRNA expression increased during atherogenesis. The expression levels (protein and mRNA levels) of TGF-beta1 were decreased from NL to the FS group while, strong protein-staining and signal of mRNA expression in P and CL groups were observed. Our findings suggest a crucial role of VEGF-A in the development of coronary artery disease. The high protein and mRNA expression levels of TGF-beta1 in P and CL suggest that this factor may be implicated in the deposition of excessive extracellular matrix in the intima of the vessel wall, contributing to the expansion of the atheromatic plaque.

Classification of arterial plaque by spectral analysis in remodelled human atherosclerotic coronary arteries

We aimed to characterise and to identify the predominant plaque type in vivo using unprocessed radiofrequency (RF) intravascular ultrasound (US) backscatter, in remodelled segments of human atherosclerotic coronary arteries. A total of 16 remodelled segments were identified using a 30-MHz intravascular ultrasound (IVUS) scanner in vivo. Of these, 9 segments were classified as positively remodelled (> 1.05 of the total vessel area in comparison with the proximal and distal reference segments) and 7 as negatively remodelled (< 0.95 of reference segment area). Spectral parameters (maximum power, mean power, minimum power and power at 30 MHz) were determined and plaque type was defined as mixed fibrous, calcified or lipid-rich. Positively remodelled segments had a larger total vessel area (16.5 ± 1.1 mm 2 vs. 8.7 ± 0.9 mm 2, p < 0.01) and plaque area (7.3 ± 1.1 mm 2 vs. 4.4 ± 0.8 mm 2, p = 0.05) than negatively remodelled segments. Both positively and negatively remodelled segments had a greater percentage of fibrous plaque ( p < 0.01) than calcified or lipid-rich plaque. Comparing positively and negatively remodelled segments, there was no significant difference between the proportion of fibrous, calcified or lipid-rich plaque. We have been able to characterise and to identify plaque composition in vivo in human atherosclerotic coronary arteries. Our data suggest that remodelled segments are predominantly composed of fibrous plaque, as identified by RF analysis, although plaque composition is similar, irrespective of the remodelling type. (E-mail: a.mcleod@ed.ac.uk)

Propofol and thiopental attenuate the contractile response to vasoconstrictors in human and porcine coronary artery segments.

The effects of propofol and thiopental on three vasoconstrictors, acetylcholine, histamine, and serotonin were studied in isolated porcine and human coronary artery rings. Propofol and thiopental attenuated the contractile response to all mediators in a dose-dependent manner. This dilating effect was fairly weak using low concentrations (propofol 1 microg mL-1 and 10 microg mL-1, thiopental 5 microg mL-1 and 10 microg mL-1). In the presence of high concentrations (propofol 100 microg mL-1, thiopental 50 microg mL-1) marked relaxation was observed (propofol -32% up to -49%, P < 0,05; thiopental -23% up to -67%, P < 0.05). These dilating effects were seen both in intact and denuded rings, the differences were not significant. Human coronary artery segments were relaxed by thiopental (-22% to -76%) and propofol (-11% to -67%) to a similar extent. Our data indicate that propofol and thiopental relax isolated coronary segments in a dose-dependent manner, and that there is no evidence that these effects are dependent of endothelial factors.

Propofol and thiopental attenuate the contractile response to vasoconstrictors in human and porcine coronary artery segments

Propofol and thiopental attenuate the contractile response to vasoconstrictors in human and porcine coronary artery segments

Influence of ageing on vasomotor responses of human epicardial coronary arteries.

Vasomotor responses to various agonists were studied on isolated circular segments of human epicardial coronary arteries from three different age groups; 23-38 years, 40-58 years and 63-86 years. Noradrenaline had no or only weak contractile effect on coronary arteries from younger patients but induced contraction of all artery segments from older patients. The Emax value was significantly (P<0.0001) higher in arteries from the oldest group compared to each of the two younger age groups, whereas the potency was similar in all three groups. Linear regression analysis of noradrenaline-induced contraction in individual patients revealed a significantly positive age-correlation (correlation coefficient 0.67, P<0.0001). Contraction induced by endothelin-1 and relaxation induced by substance P, calcitonin gene-related peptide and vasoactive intestinal peptide on arteries precontracted with U46619 showed no significant differences in maximum responses and potencies between the three age groups, and no significant linear age-correlation. These data demonstrate a large variability in contractile responses to noradrenaline with contractions seen mostly in coronary arteries from older patients. It thus seems that sympathetic activation could contribute to coronary ischaemia in some patients.

Magnesium and cardiovascular disease.

Magnesium and cardiovascular disease.

Modulation of Ca 2+-activated K + channels in human vascular cells by insulin and basic fibroblast growth factor

Insulin and basic fibroblast growth factor (bFGF) play an important role in the pathogenesis of atherosclerosis and have been shown to have vasodilatory effects. Since modulation of vascular ion channels determines membrane potential and thereby influences essential Ca2+-dependent intracellular pathways, we have investigated the effect of insulin and bFGF on Ca2+-activated K+ channels (BKCa) in human umbilical vein endothelial cells (HUVEC) and smooth muscle cells. The latter were obtained from either atherosclerotic plaques (SMCP) or from media segments (SMCM) of human coronary arteries. Using the patch-clamp technique, insulin (100 microU/ml) caused a significant increase in BKCa open-state probability in SMCP and HUVEC, whereas no significant changes were observed in SMCM. Basic FGF (30 ng/ml) revealed a significant increase in BKCa activity in HUVEC and a significant decrease in the BKCa open-state probability in SMCP, but caused no changes in SMCM. Thus, growth factors modulate vascular BKCa in a cell-type specific manner, which may be of importance concerning vasoactive and atherogenic effects of growth factors.

Differences in the Distribution of Versican, Decorin, and Biglycan in Atherosclerotic Human Coronary Arteries

The distributions of versican, biglycan, and decorin have been examined in segments of normal and atherosclerotic human coronary arteries using antibodies directed against the core proteins of these macromolecules. Versican immunostaining was prominent throughout the extracellular matrix (ECM) in regions of the vessels that contained abundant smooth-muscle cells, such as in diffuse intimal thickenings, fibrous caps, and in zones of loose, myxoid connective tissue. Versican also was present in smooth-muscle–rich thrombi and at borders of the lipid-rich cores of advanced atherosclerotic lesions. Biglycan immunostaining was observed in diffuse intimal thickenings, fibrous caps, and myxoid areas, but, unlike versican, it was abundant in the lipid-rich core of advanced plaques. However, biglycan immunostaining was absent in smooth-muscle cell–enriched thrombi. Decorin immunostaining paralleled biglycan immunostaining except that it was conspicuously absent in the myxoid areas of the plaque and markedly reduced in diffuse intimal thickenings. Both biglycan and decorin immunostaining were consistently associated with some of the microvessels in the thrombi and in advanced atherosclerotic plaques. Taken together, these results indicate that specific proteoglycans distribute to topographically defined regions of normal and atherosclerotic human coronary arteries and that these different distributions may indicate a diversity of functions in normal and pathologic processes of the arterial wall.

Determination of human coronary artery composition by Raman spectroscopy.

We present a method for in situ chemical analysis of human coronary artery using near-infrared Raman spectroscopy. It is rapid and accurate and does not require tissue removal; small volumes, approximately 1 mm3, can be sampled. This methodology is likely to be useful as a tool for intravascular diagnosis of artery disease. Human coronary artery segments were obtained from nine explanted recipient hearts within 1 hour of heart transplantation. Minces from one or more segments were obtained through grinding in a mortar and pestle containing liquid nitrogen. Artery segments and minces were excited with 830 nm near-infrared light, and Raman spectra were collected with a specially designed spectrometer. A model was developed to analyze the spectra and quantify the amounts of cholesterol, cholesterol esters, triglycerides and phospholipids, and calcium salts present. The model provided excellent fits to spectra from the artery segments, indicating its applicability to intact tissue. In addition, the minces were assayed chemically for lipid and calcium salt content, and the results were compared. The relative weights obtained using the Raman technique agreed with those of the standard assays within a few percentage points. The chemical composition of coronary artery can be quantified accurately with Raman spectroscopy. This opens the possibility of using histochemical analysis to predict acute events such as plaque rupture, to follow the progression of disease, and to select appropriate therapeutic interventions.

Mechanical properties and effects of sympathetic co-transmitters on human coronary arteries and veins.

Active isometric wall tension was studied at different levels of passive wall tension in isolated circular 2 mm long segments of human epicardial coronary arteries and veins, and maximum active wall tension was calculated to 6.60 mN/ mm for arteries and 0.86 mN/mm for veins. Vasomotor responses to sympathetic co-transmitters were studied at resting tension and after precontraction with U46619. Noradrenaline (NA) and adenosine 5'-triphosphate (ATP) induced strong contractions of veins, whereas relaxant responses dominated in arteries. Isoprenaline potently relaxed all arteries and veins. Prazosin and rauwolscine in a concentration of 10(-7) M both competitively antagonized NA-induced contraction of arteries and veins. For uridine 5'-triphosphate (UTP), relaxant responses were demonstrated in most arteries but only some veins. Neuropeptide Y (NPY) elicited no observable vasomotor responses in either arteries or veins. Mechanical removal of the arterial endothelium did not significantly alter relaxant responses to NA, ATP, UTP or isoprenaline. In conclusion, alpha 1- and alpha 2-adrenoceptors mediating contraction and beta-adrenoceptors mediating relaxation seem to be present in both human epicardial coronary arteries and veins. When applied to isolated epicardial coronary vessels, NA and ATP had a stronger influence on vasomotor tone than NPY and UTP, mediating strong contraction of veins but mainly relaxation of coronary arteries, that was independent of an intact endothelium.

5‐HT1D receptor agonists and human coronary artery reactivity in vitro: crossover comparisons of 5‐HT and sumatriptan with rizatriptan and L‐741,519

1Rizatriptan (MK‐462, (N,N‐dimethyl‐2‐[5‐(1,2,4‐triazol‐1‐ylmethyl)‐1H‐indol‐3‐yl]ethylamine)) and its structurally related analogue L‐741,519 (N‐methyl‐4‐[5‐(1,2,4‐triazol‐4‐yl)‐1H‐indol‐3‐yl]piperidine) are novel 5‐HT1D‐receptor agonists. Rizatriptan has shown efficacy as an anti‐migraine agent in clinical trials. Since angiographic studies in patients have shown that sumatriptan (an established 5‐HT1D‐receptor agonist) can cause coronary artery vasoconstriction, we compared the effects of rizatriptan and L‐741,519 with those of 5‐HT and sumatriptan on endothelium‐denuded segments of human coronary artery in vitro. 2Coronary arteries were obtained from explanted hearts from patients undergoing cardiac transplantation (n=16 viable arteries from 13 males, 3 females, aged 38–68 years) and arterial segments (5–6 mm in length) were mounted in organ baths for isometric tension recording. Each segment was first exposed to 45mm KCl and then to 5‐HT (1 nm–100 μm). Concentration–effect curves to rizatriptan and sumatriptan (Study 1, n=6 or 7 arteries) or sumatriptan and L‐741,519 (Study 2, n=8 arteries) were then performed in a consecutive and random manner. The response to repeated application of 5‐HT was obtained in separate segments. 3One artery showed severe atheroma and was not included in the analysis. ANOVA showed that 5‐HT responsiveness varied significantly between arteries from different patients, but not between arterial segments from the same patient. Desensitization was seen consistently across all agonists but did not significantly affect inter‐agonist comparisons. 4There was graded effectiveness in the ability of the agonists to cause contraction with the rank order of Emax values being 5‐HTsumatriptan&gt;L‐741,519&gt;rizatriptan. In terms of EC50 values, L‐741,519 was significantly more potent than sumatriptan. 5The present study (using a ‘cross‐over’ experimental protocol) confirms our previous observation that rizatriptan is less effective than sumatriptan in causing contraction of human isolated coronary artery. Furthermore, it shows that the lower maximum contractile response to rizatriptan, compared with that of sumatriptan, is not merely the consequence of variability in response to 5‐HT1D‐ receptor agonists between patients or between segments from the same artery.

Endothelin-A and -B receptors in human coronary arteries and veins

Using reverse transcriptase-polymerase chain reaction, products corresponding to mRNA encoding endothelin-A and -B (ET A and ET B) receptors were demonstrated in human coronary arteries and veins with intact endothelium and in endothelium-denuded human coronary arteries. Vasomotor responses were studied on isolated segments of human epicardial coronary arteries and veins at resting tension and after precontraction with U46619. In both arteries and veins, endothelin-1 (ET) induced strong and potent contractions, and preincubation with different concentrations of the non-selective ET A/ET B receptor antagonist PD 145065 caused a rightward shift of the concentration-response curves without significantly changing maximum responses (p A 2 value 6.7 arteries, 7.4 veins). The ET B receptor agonist IRL 1620 induced no contraction of arteries or veins at resting tension, but induced weak relaxation of all arteries and most precontracted veins, the relaxation being endothelium-dependent in arteries. ET at low concentrations induced weak relaxations of most precontracted arteries, but no veins. In conclusion, mRNA encoding ET A and ET B receptors is present in human coronary arteries and veins, ET A receptors mediating contraction and ET B receptors mediating relaxation. In arteries, mRNA for both receptor types was detected in the media, but ET B receptor-mediated relaxation was endothelium-dependent.

Up-Regulation of Endothelin-B Receptors in Atherosclerotic Human Coronary Arteries

Both endothelin-A (ETA) and endothelin-B (ETB) receptors are known to be present in human coronary arteries. However, their absolute and relative amounts, functional roles, and the influence of pathology are uncertain. The goal of the present study was to characterize endothelin receptors mediating constriction in human coronary arteries and to assess the influence of cardiomyopathy (CMP) and coronary artery disease (CAD) on ET receptors in human tissue. For comparison, porcine coronary arteries were evaluated in parallel. Competition binding experiments using [125I]ET-1 and different selective and nonselective ETA- and ETB-receptor agonists or antagonists revealed similar relative densities (relative Bmax) of ETA and ETB receptors in coronary arteries from human cardiomyopathic hearts (83% ETA and 17% ETB; n = 5) and porcine hearts (78% ETA and 22% ETB; n = 5). In marked contrast, the relative Bmax of ETB receptors were significantly higher in coronary arteries from human atherosclerotic hearts (51% ETA and 49% ETB; n = 3). Total receptor density (Bmax; fmol/mg protein) was highest in porcine (385 +/- 29) arteries, followed by human CAD (253 +/- 41) and CMP (174 +/- 20) coronary arteries. The relative and absolute Bmax values for ETA and ETB receptors in coronary arteries from a donor heart were similar to those obtained in CMP hearts. There were no significant differences in affinity constants (KD) values for ET-1, ET-3, Sarafotoxin S6c (SRTX S6c), BQ-123, and bosentan (Ro 47-0203) between tissues. In human coronary arteries from CMP hearts, ET-induced constriction seemed to be solely mediated via ETA receptors. In contrast, in porcine coronary arteries 20% of the maximal effect mediated by ET-1 could be attributed to ETB receptors, in agreement with the binding data. The functional role of ETB receptors in CAD tissue could not be evaluated because of the occurrence of spontaneous phasic contractions. We conclude that ETB receptors are up-regulated in human atherosclerotic coronary arteries. Further studies are needed to determine the pathophysiological importance of these receptors.

A comparison of the contractile effects of 5-hydroxytryptamine, sumatriptan and MK-462 on human coronary artery in vitro.

1. MK-462 (N,N-dimethyl-2-[5-(1,2,4-triazol-1-ylmethyl)-1H- indol-3-yl]ethylamine) is a novel selective 5-HT1D-receptor agonist which in clinical trials has been shown to be an effective antimigraine agent. As angiographic studies have shown that sumatriptan (an established 5-HT1D-receptor agonist) can cause coronary artery vasoconstriction in patients, we compared the effects of MK-462 with those of 5-HT and those of sumatriptan, on isolated segments of human coronary artery in vitro. 2. Coronary arteries were obtained from explanted hearts from patients (n = 22, 2 females, 20 males, aged 21-60 years) undergoing cardiac transplantation. Endothelium-denuded ring segments of coronary artery, 2mm long were mounted in organbaths for isometric tension recording. For each arterial ring segment, a cumulative concentration-effect curve to either 5-HT, sumatriptan or MK-462 was determined. After maximal response to each agonist had been obtained, ketanserin (a 5-HT2 receptor antagonist) 0.6 microM was added to the tissue bath, followed by methiotepin (0.6 microM) and the reduction in tension produced by the addition of each antagonist was determined. 3. Out of 22 coronary arteries studied, only 10 showed any response (contraction) to 5-HT. Not all arteries which responded to 5-HT contracted in response to both sumatriptan and MK-462 (one ring from each artery being exposed to a single agonist in each case).(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary Vascular and Antiplatelet Effects of Peroxynitrite in Human Tissues

The present study investigated the interrelationship between nitric oxide and its intermediate degradation product, peroxynitrite, on reactivity of isolated human coronary arteries and washed human platelets. Ninety-one ring segments of human coronary arteries, with minimal intimal proliferation, were isolated from 9 patients who underwent cardiac transplantation. All vessels were pretreated with 5 μM indomethacin and precontracted with 0.5-1 μM prostaglandin F2α. Addition of 0.01-300 μM peroxynitrite produced a rapid and dose-dependent relaxation similar to that observed with isolated canine coronary arteries. The IC50 of peroxynitrite induced relaxation was 3.2 ± 0.3 μM. Superoxide dismutase (SOD, 100 u/ml) enhanced, while hemoglobin (3 μM) inhibited, the observed relaxation and changed the IC50 to 0.5 ± 0.1 μM and 63 ± 9.4 μM, respectively. In washed human platelets, addition of 1-100 μM peroxynitrite by itself did not produce any direct effect on platelets, but resulted in a dose-dependent inhibition ...

Diffuse calcification in human coronary arteries. Association of osteopontin with atherosclerosis.

Coronary atherosclerosis is frequently associated with calcification of arterial plaque. To understand the mechanisms responsible for the formation of atherosclerotic calcification, we examined human coronary arteries for the presence and extent of mineral. In sections stained specifically for mineral, staining was diffuse and present in all atherosclerotic plaques. Hydroxyapatite was not detected in normal coronary artery sections. Distribution of hydroxyapatite coincided with a similar distribution of calcium detected by a radiodense pattern using contact microradiography of the same sections before cytochemical staining. By energy-dispersive x-ray microanalysis, the chemical composition of calcified sites was identical to hydroxyapatite (Ca10[PO4]6[OH]2), the major inorganic component of bone. Osteopontin is a phosphorylated glycoprotein with known involvement in the formation and calcification of bone and is regulated by local cytokines. Human coronary artery segments (14 normal and 34 atherosclerotic) obtained at autopsy were evaluated immunohistochemically using polyclonal antibodies generated against human osteopontin. Immunohistochemistry for osteopontin indicated intense, highly specific staining in the outer margins of all diseased segments at each calcification front; staining was evident throughout the entire plaque. Conversely, arterial segments free of atheroma and calcification and sections treated with nonimmune serum had no evidence of positive staining. Osteopontin, a protein involved in mineralization is specifically associated with calcific coronary atheroma and may play an important role in the onset and progression of this disease in human coronary arteries. The deposition of noncollagenous proteins such as osteopontin may regulate the presence or absence of calcification and ultimately alter vessel compliance.

Halothane Relaxes Previously Constricted Human Epicardial Coronary Artery Segments More Than Isoflurane

To compare the vasodilatory effects of isoflurane versus halothane on coronary arteries in vitro, we studied the capacity of isoflurane and halothane to relax resting and previously constricted human coronary artery segments with use of in vitro tension recording. Human epicardial coronary artery segments (1.5-2.0 mm outside diameter) were obtained from hearts excised from recipient patients at time of heart transplantation. The effects of 0.5%, 1.0%, 2.0%, and 3.0% isoflurane or halothane on resting coronary artery segments stretched to their optimal resting tension were determined. Next, after removal of anesthetic from the bathing solution, the segments were constricted with K+ (60 mM), and this contraction was allowed to plateau. The arteries were then again exposed to isoflurane or halothane at 0.5%, 1.0%, 2.0%, and 3.0% concentrations. Isoflurane and halothane had no effect on noncontracted coronary artery segments stretched to their optimal resting tension. Halothane caused significant relaxation of K(+)-induced (60 mM) contractions at 2.0% and 3.0% but not at lower concentrations. Isoflurane did not cause significant relaxation of K(+)-induced (60 mM) contractions at any concentration studied. Our studies indicate that under the conditions studied, isoflurane at clinically relevant concentrations is not a significant coronary dilator.

Assessment of endothelium-derived relaxing factor from human coronary arteries using the anti-platelet aggregatory effect.

Responses of human and canine washed platelets to thrombin in the presence and absence of human and canine coronary arteries were examined to establish a simple indirect measurement system for endothelium-derived relaxing factor (EDRF). Isolated rings of coronary arteries were obtained from either adult dogs or recipient hearts of cardiac transplant patients. The addition of small segments of canine and human coronary arteries with intact endothelia inhibited thrombin-induced platelet aggregation, but those with disrupted endothelia did not. Pretreatment of human and canine coronary arteries with the cyclo-oxygenase inhibitor indomethacin markedly attenuated the observed effect. The anti-platelet aggregatory effect of indomethacin-pretreated coronary artery was enhanced by acetylcholine or histamine, stimulators of EDRF production, or superoxide dismutase, which prolongs the half-life of EDRF, and inhibited by the EDRF inhibitor hemoglobin. These results suggest that endothelial cells of the human coronary artery, like the canine coronary artery, can produce EDRF which inhibits platelet aggregation, and that this simple experimental model is useful to examine the effect of environmental chemicals on EDRF in the human coronary artery.