Preservation of endothelium-dependent vasodilation in the spastic segment of the human epicardial coronary artery by substance P

Vasospastic Angina: A Contemporary Review of its Pathophysiology, Diagnosis and Management

Nearly 40% of patients presenting to the catheter laboratory with angina have non-obstructed coronary arteries (ANOCA), an umbrella term that encompasses distinct pathophysiological entities, such as coronary artery spasm. Coronary artery spasm leads to sudden reversible coronary flow attenuation, which clinically manifests as vasospastic angina (VSA). VSA is associated with poor quality of life and an increased risk of major adverse cardiac events. However, the pathophysiological mechanisms underlying this phenomenon are incompletely understood, which has resulted in limited therapeutic options for patients afflicted with this condition. The past decade has seen a surge in new research being conducted in the field of ANOCA and VSA. This review article provides a comprehensive summary of the underlying pathophysiological mechanisms of VSA and the current therapeutic options. We also appraise the current diagnostic approach in patients with suspected VSA.

Coronary Artery Spasm: The Interplay Between Endothelial Dysfunction and Vascular Smooth Muscle Cell Hyperreactivity

Patients with angina pectoris, the cardinal symptom of myocardial ischaemia, yet without significant flow-limiting epicardial artery stenosis represent a diagnostic and therapeutic challenge. Coronary artery spasm (CAS) is an established cause for anginal chest pain in patients with angiographically unobstructed coronary arteries. CAS may occur at the epicardial level and/or in the microvasculature. Although the underlying pathophysiological mechanisms of CAS are still largely unclear, endothelial dysfunction and vascular smooth muscle cell (VSMC) hyperreactivity seem to be involved as major players, although their contribution to induce CAS is still seen as controversial. This article will look at the role and possible mechanistic interplay between an impaired endothelial and VSMC function in the pathogenesis of CAS.

2014 Williams Harvey Lecture: importance of coronary vasomotion abnormalities-from bench to bedside

Coronary vasomotion abnormalities play important roles in the pathogenesis of ischaemic heart disease, in which endothelial dysfunction and coronary artery spasm are substantially involved. Endothelial vasodilator functions are heterogeneous depending on the vessel size, with relatively greater role of nitric oxide (NO) in conduit arteries and predominant role of endothelium-derived hyperpolarizing factor (EDHF) in resistance arteries, where endothelium-derived hydrogen peroxide serves as an important EDHF. The functions of NO synthases in the endothelium are also heterogeneous with multiple mechanisms involved, accounting for the diverse functions of the endothelium in vasomotor as well as metabolic modulations. Cardiovascular abnormalities and metabolic phenotypes become evident when all three NO synthases are deleted, suggesting the importance of both NO and EDHF. Coronary artery spasm plays important roles in the pathogenesis of a wide range of ischaemic heart disease. The central mechanism of the spasm is hypercontraction of vascular smooth muscle cells (VSMCs), but not endothelial dysfunction, where activation of Rho-kinase, a molecular switch of VSMC contraction, plays a major role through inhibition of myosin light-chain phosphatase. The Rho-kinase pathway is also involved in the pathogenesis of a wide range of cardiovascular diseases and new Rho-kinase inhibitors are under development for various indications. The registry study by the Japanese Coronary Spasm Association has demonstrated many important aspects of vasospastic angina. The ongoing international registry study of vasospastic angina in six nations should elucidate the unknown aspects of the disorder. Coronary vasomotion abnormalities appear to be an important therapeutic target in cardiovascular medicine.

Recent insights into the mechanisms of vasospastic angina

Coronary artery spasm plays an important role in the pathogenesis of many types of ischemic heart disease, not only in vasospastic angina but also in myocardial infarction and sudden death, particularly in the asian population. Patients with vasospastic angina are known to have defective endothelial function due to reduced nitric oxide bioavailability. Moreover, markers of oxidative stress and plasma levels of C-reactive protein are elevated. Smoking, polymorphysms of endothelial nitric oxide synthetase (eNOS), and low-grade inflammation have been regarded as the most important risk factors for vasospastic angina. The recent body of evidence indicates that RhoA and its down stream effector, ROCK/Rho-kinase, are associated with hypercontraction of vascular smooth muscle of the coronary artery and regulation of eNOS activity. Thus, endothelial dysfunction through abnormalities of eNOS and enhanced contractility of vascular smooth muscle in coronary artery segments are considered major mechanisms in vasospastic angina. However, the precise mechanisms for coronary vasospasm are not well understood. This article will review current understanding of the mechanism of coronary artery spasm.

Lack of association between the insertion/deletion polymorphism of the angiotensin-converting enzyme gene and vasospastic angina

BACKGROUND AND HYPOTHESIS

It has been suggested that the insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme (ACE) gene is an independent risk factor for coronary atherosclerosis and myocardial infarction, but its relation to vasospastic angina has not been fully proven. In the present study, we investigated the possible relationship between the ACE I/D genotype and vasospastic angina.

METHODS

We explored the distribution of the ACE genotype in 20 patients with vasospastic angina without fixed coronary artery stenosis, 55 angina patients with fixed coronary artery stenosis, and 30 control subjects without coronary artery disease.

RESULTS

The frequency of the DD genotype in patients with vasospastic angina (DD: 30.0%, ID: 20.0%, II: 50.0%) did not differ from that in the control subjects (DD: 23.3%, ID: 26.7%, II: 50.0%), while the frequency in patients with coronary artery stenosis (DD: 43.7%, ID: 21.8%, II: 34.5%) was significantly higher than that in the control subjects. The frequency of the D allele also did not differ between patients with vasospastic angina (0.40) and control subjects (0.37), while the frequency was significantly higher in patients with coronary artery stenosis (0.55).

CONCLUSIONS

These findings suggest that the ACE DD genotype is a potent genetic risk factor for organic coronary artery disease, while it confers no appreciable increase in risk of vasospastic angina. These results also suggest the diversity of the pathogenesis of vascular lesions in these two types of coronary artery disease.

Airway hyperresponsiveness in patients with coronary spastic angina: relationship between coronary spasticity and airway responsiveness

BACKGROUND

Several reports have suggested a possible link between bronchial asthma and coronary spasm, but the possibility of a relationship in coronary spastic angina (CSA) has not been clarified.

METHODS AND RESULTS

Airway responsiveness to methacholine and coronary spasticity to acetylcholine were examined in 42 patients with CSA and 36 patients with chest pain syndrome (CP). Furthermore, 18 control subjects were examined and their airway responsiveness compared with that of the CSA and CP patients. The incidence of airway hyperresponsiveness was significantly higher in the CSA group (74%) than in the CP (19%) and control (17%) groups (p<0.0001). The geometric mean of the log minimum dose (Dmin), defined as the cumulative dose at the point at which respiratory conductance began to decrease, was significantly lower in the CSA group (0.75 log units) than in the CP (1.20 log units) and control (1.38 log units) groups (p=0.004).

CONCLUSION

These results demonstrate that acetylcholine-induced coronary spasticity is significantly related to methacholine-induced airway responsiveness in patients with CSA. A generalized hyperresponsiveness of the vascular and nonvascular smooth muscles, including that through cholinergic mechanisms, may exist in patients with CSA.

Specificity of vascular reactivity and remodeling after repeated endothelial injury in a swine model

We investigated the difference in vascular responses and remodeling between coronary and iliac arteries after repeated endothelial denudation. Endothelial denudation of the left anterior descending coronary artery (LAD) and the right common iliac artery (RIA) was repeated 4 times twice a month using a Fogarty catheter in 21 pigs. Vascular responses to vasoactive drugs were evaluated as % luminal diameter changes on contrast angiography 2 weeks after the last denudation. Corresponding nondenuded sites, ie, the left circumflex coronary artery (LCX) and the left common iliac artery (LIA), were used as references. Acetylcholine (1 microg/kg) did not constrict the LCX (0 +/- 1%) and the LAD (1 +/- 1%, P < 0.05), whereas it constricted the RIA (20 +/- 6%) but not the LIA (-3 +/- 3%, P < 0.01). Alternatively, serotonin (10 microg/kg) constricted the LAD strikingly (88 +/- 5%, P < 0.01 versus LCX and RIA), as well as the RIA (35 +/- 10%, P < 0.05 versus LIA). Vasodilator responses to substance P and isosorbide dinitrate were not different after injury in both arteries. The intima-to-media ratio and adventitia-to-media ratio of the relevant site in cross section of tissue sample from LAD were greater than those from LCX, and were more prominent than those from RIA. The results show that vascular tone regulation after the endothelial injury and vascular remodeling might be altered in a vessel-specific manner.

Modulation of contractions to ergonovine and methylergonovine by nitric oxide and thromboxane A2 in the human coronary artery

This study explored the modulatory effects of nitric oxide and thromboxane A2 on contractions to ergonovine and methylergonovine in human coronary arteries. To elucidate the different role of nitric oxide synthase in the response to the ergot alkaloids, the serotonin (5-HT) receptors involved in nitric oxide synthase in the response to the ergot alkaloids, the 5-HT receptors involved in nitric oxide release and the contraction of the vascular smooth muscle were characterized with more selective 5-HT-receptor agonists and antagonists. Rings of human coronary arteries from explanted hearts were suspended in organ chambers for isometric tension recording. After testing for contractile (potassium chloride, 60 mM) and endothelial function (substance P, 10(-8) M), respectively, they were exposed to ergot alkaloids or other agonists in the absence or presence of U 46619 (10(-9) M), or nitro-L-arginine (10(-4) M), or both. Ergonovine and methylergonovine were comparable, weak vasoconstrictors in untreated preparations. Contractions to ergonovine were augmented by U 46619, but not by nitro-L-arginine. Contractions to methylergonovine were augmented only by combining U 46619 and nitro-L-arginine. Serotonin and methylergonovine, but not ergonovine, elicited endothelium-dependent, nitric oxide-mediated relaxations. Nonselective 5-HT(1B/1D)-receptor stimulation caused both contractions and relaxations; selective 5-HT1B stimulation caused relaxations only. In the human coronary artery, contractions to ergonovine are not dependent on NO release but are synergistically augmented by thromboxane. Methylergonovine causes similar effects on the vascular smooth muscle, but contractions are inhibited by the release of NO from the endothelium. The 5-HT receptor on the endothelium appears to be different from the receptor on the vascular smooth muscle, which mediates the contractile response to the ergot alkaloids.

Cellular and molecular mechanisms of coronary artery spasm: lessons from animal models

Coronary artery spasm plays an important role in the pathogenesis of a wide variety of ischemic heart diseases, especially in the Japanese population. Because coronary artery spasm can be induced by a variety of stimuli with different mechanisms of action, the occurrence of the spasm appears to be due to the local hyperreactivity of the coronary artery rather than to an enhanced stimulation with a single mechanism of action. Several lines of evidence indicate that coronary artery spasm is caused primarily by smooth muscle hypercontraction whereas the contribution of endothelial dysfunction may be minimal. In order to elucidate the cellular and molecular mechanisms of the spasm, porcine models of the spasm were developed. In the first model with balloon injury and high-cholesterol feeding, a close topological correlation between the early atherosclerotic lesions and the spastic sites was noted, whereas in the second model with an inflammatory cytokine the potential importance of coronary inflammatory changes, especially at the adventitia, was noted. Subsequent studies in vivo and in vitro demonstrated that protein kinase C (PKC) and Rho-kinase are substantially involved in the intracellular mechanism of the spasm, resulting in increases in the mono- and diphosphorylations of myosin light chain (MLC). Furthermore, molecular biological analyses demonstrated that Rho-kinase is upregulated at the spastic site (at all levels, including mRNA, protein, and activity), resulting in the inhibition of MLC phosphatase through the phosphorylation of its myosin binding subunit and thereby causing the increase in MLC phosphorylations. Preliminary results also suggest that the long-term inhibition of Rho-kinase is effective in inhibiting the development of arteriosclerotic vascular lesions in several porcine models. Thus, Rho-kinase could be regarded as a novel therapeutic target for coronary arteriosclerosis in general and coronary artery spasm in particular.

Systemic endothelial function is preserved in men with both active and inactive variant angina pectoris

To test the hypothesis that coronary spasm could be a coronary manifestation of systemic endothelial dysfunction and that the activity of coronary spasm could influence systemic endothelial function, we examined brachial flow-mediated, endothelium-dependent vasodilation and nitroglycerin-induced endothelium-independent vasodilation with high-resolution ultrasound in 11 men with variant angina pectoris (6 active and 5 inactive) without established coronary atherosclerosis. Endothelium-dependent vasodilation in peripheral circulation was preserved in men with active and inactive variant angina pectoris, suggesting that systemic endothelial dysfunction is not involved in either the pathogenesis or the activity of coronary spasm.

Endothelial vasodilator function is preserved at the spastic/inflammatory coronary lesions in pigs

BACKGROUND

The question of whether or not endothelial vasodilator function in the spastic coronary artery is preserved is still controversial. We recently developed a porcine model in which long-term and local treatment with interleukin-1beta (IL-1beta) from the adventitial site causes coronary arteriosclerotic changes and vasospastic responses to autacoids. The aim of this study was to examine the endothelial vasodilator function in our new porcine model of the spasm both in vivo and in vitro.

METHODS AND RESULTS

A segment of the porcine coronary artery was aseptically wrapped with cotton mesh that held absorbed IL-1beta-bound microbeads. Two weeks after the procedure, intracoronary administration of serotonin caused coronary vasospasm at the IL-1beta-treated site (n = 10). Coronary vasodilatation to bradykinin, substance P, or an increase in coronary blood flow was preserved at the spastic site. Vasodilator responses to 3-morpholinosydnonimine (an NO donor) and nitroglycerin also were comparable between the 2 sites. The vasoconstricting response to N(G)-monomethyl-L-arginine and the extent of the augmentation of the serotonin-induced vasoconstriction were comparable between the 2 sites. Organ chamber experiments showed that endothelium-dependent relaxations to bradykinin, the calcium ionophore A23187, and even the vasospastic agonist serotonin were preserved at the spastic site, whereas contractions to serotonin were augmented at the spastic site regardless of the presence or absence of the endothelium (n = 6). Endothelium-independent relaxations to sodium nitroprusside were also preserved at the spastic site.

CONCLUSIONS

These results indicate that endothelial vasodilator function is preserved at the spastic site and that the spasm is caused primarily by smooth muscle hypercontraction in our porcine model.

[Coronary spasm--a clinically relevant problem?]

Coronary spasms are defined as reversible coronary stenosis, which limits coronary blood flow under resting conditions. The demonstration of either spontaneous or provoked coronary spasm proves coronary hypercontractility and thus the diagnosis of variant angina. Several stimuli can provoke coronary vasospasm, but the highest sensitivity and specificity has been shown with ergonovine. Alternatively acetylcholine or with less sensitivity, but high specificity, hyperventilation may be employed. Typically coronary vasospasm presents with angina pectoris at rest; the manifestation with myocardial infarction or syncope are of great clinical importance. The prevalence of the disease is unknown due to the rarely performed provocation tests in Western countries. The incidence of positive test results strongly depends on the symptoms of the patients; from 0% in patients without any evidence for myocardial ischemia up to 54% in patients with typical angina at rest have been observed. Coronary vasospasm is closely related to atherosclerotic coronary artery disease, since intravascular ultrasound studies reveal atherosclerotic plaques in almost any spastic segment. Risk factors for coronary artery disease and coronary vasospasm, however, differ profoundly. For the latter cigarette smoking is the only established risk factor. Although several candidates and predisposing factors (serotonin, histamine, thromboxane, endothelin) have been described, the mediators and the pathogenesis of the disease remains unknown. Endothelial dysfunction alone is not sufficient to explain the features of variant angina. Some evidence supports the hypothesis of local inflammation. The mortality in variant angina depends on the extent of the coronary artery disease. Pure coronary vasospasm does not lead to increased mortality; patients with highly active disease presenting with syncope may have an increased risk. Medical treatment should include long-acting calcium antagonists or nitrates, beta-blockers may even favor the occurrence of ischemic attacks. Although the benefit has not been proven, the use of aspirin may considered in highly active disease.

Short-term estrogen augments both nitric oxide-mediated and non-nitric oxide-mediated endothelium-dependent forearm vasodilation in postmenopausal women

Estrogen is known to improve in the short term the impaired endothelium-dependent vasodilating responses in postmenopausal women, which may account in part for the beneficial cardiovascular effects of the female hormone. Endothelium-dependent vasodilation is achieved by combined effects of endothelium-derived prostacyclin, nitric oxide (NO), and hyperpolarizing factor. In this study, we investigated our hypothesis that short-term estrogen improves both NO-mediated and non-NO-mediated endothelium-dependent vasodilation in postmenopausal women. The study included 12 postmenopausal women (aged 64 +/- 3 years). The forearm blood flow was measured by strain-gauge plethysmography. The forearm vascular responses to the endothelium-dependent vasodilators, acetylcholine and substance P, were examined before and after intravenous administration of conjugated estrogen and subsequently after intraarterial infusion of NG-monomethyl-L-arginine (L-NMMA), an inhibitor of NO synthesis. Short-term estrogen augmented the forearm vasodilating responses to both acetylcholine and substance P. The treatment with L-NMMA almost abolished the augmented response to acetylcholine but did not affect that to substance P. The forearm vascular response to sodium nitroprusside was unchanged by the estrogen administration. These results indicate that estrogen augments (in the short-term) both NO-mediated and non-NO-mediated endothelium-dependent forearm vasodilation in postmenopausal women. Thus the beneficial effect of estrogen on endothelial vasodilator function appears to extend to non-NO-dependent mechanism(s).

Role of nitric oxide in substance P-induced vasodilation differs between the coronary and forearm circulation in humans

It has been shown that substance P causes endothelium-dependent vasodilation in the human coronary and forearm vessels. However, the precise mechanism whereby substance P dilates the coronary and peripheral vasculatures is unknown in humans. The aim of this study was to examine whether the vasodilator effect of substance P is mediated by nitric oxide in the human coronary and forearm vessels. Eight patients with normal coronary angiograms were studied for the measurements of coronary blood flow (intracoronary Doppler guide wire and quantitative coronary arteriography) and forearm blood flow (strain-gauge plethysmograph). Intracoronary acetylcholine (10 micrograms/min for 2 min) and substance P (30 and 90 ng/min for 2 min) increased coronary blood flow from the baseline value. Intracoronary infusion of NG-monomethyl-L-arginine (L-NMMA) at 200 mumol significantly attenuated the magnitudes of increase in coronary blood flow induced by both acetylcholine (p < 0.01) and substance P (p < 0.01). Acetylcholine (4, 8, and 16 micrograms/min for 2 min) and substance P (0.8, 1.6, and 3.2 ng/min for 2 min) also increased forearm blood flow in a dose-dependent manner. Intraarterial L-NMMA (8 mumol/min for 5 min) decreased the magnitudes of increase in forearm blood flow induced by acetylcholine (p < 0.01). L-NMMA at the same dosage decreased the increase in forearm blood flow induced by substance P, but the magnitude of the inhibitory effect of L-NMMA on blood-flow responses to substance P was significantly smaller in the forearm than in coronary vessels. It is suggested that endothelium-derived nitric oxide contributes to substance P-induced vasodilation, and that the contribution of nitric oxide to substance P-induced vasodilation is smaller in the forearm than in coronary circulation.

Impaired glucose tolerance with late hypersecretion of insulin during oral glucose tolerance test in patients with vasospastic angina

OBJECTIVES

This study tested whether patients with vasospastic angina have impaired glucose tolerance or impaired insulin response.

BACKGROUND

Hyperinsulinemia has been demonstrated in patients with coronary artery disease and syndrome X.

METHODS

We performed an oral glucose tolerance test (75 g) in 30 patients with vasospastic angina in whom severe coronary vasospasm was induced by acetylcholine and in a matched group of 30 patients with atypical chest pain in whom no significant vasospasm was induced. The responses of insulin and glucose were compared between the two groups. No subjects had overt diabetes mellitus, hypertension, dyslipidemia, obesity or angiographically detected significant baseline coronary stenosis. Venous blood samples were taken during fasting and at 30, 60, 120 and 180 min after glucose load to obtain plasma glucose and immunoreactive insulin levels.

RESULTS

Impaired glucose tolerance was detected in the 19 (63%) of 30 patients with vasospastic angina and in none of 30 patients with atypical chest pain (p < 0.001). The immunoreactive insulin levels at 60 and 120 min as well as the interval to peak insulin level were significantly greater in patients with vasospastic angina (p < 0.001). Among patients with vasospastic angina, those with acetylcholine-induced multivessel coronary vasospasm showed a significantly higher sum of insulin concentrations than those with single-vessel spasm (p < 0.01). During induction of coronary spasm, 10 patients with vasospastic angina presented ventricular arrhythmias. The sum of insulin concentrations was significantly greater in patients with than in those without ventricular arrhythmias.

CONCLUSIONS

Patients with vasospastic angina exhibited a high incidence of impaired glucose tolerance and delayed and significantly higher insulin responses. These findings suggest that impaired glucose tolerance with late hypersecretion of insulin may contribute to the pathogenesis of severe coronary vasospasm.

Basal release of endothelium-derived nitric oxide at site of spasm in patients with variant angina

OBJECTIVES

The aim of this study was to investigate the basal release of nitric oxide at spastic sites in patients with variant angina.

BACKGROUND

We previously reported that endothelium-dependent dilator responses to acetylcholine, substance P and bradykinin are preserved at the site of coronary artery spasm. However, it is not known whether the basal release of endothelium-derived nitric oxide is altered at the spastic site.

METHODS

The effects of intracoronary N(G)-monomethyl-L-arginine (L-NMMA, an inhibitor of nitric oxide synthesis) at cumulative doses of 50, 100 and 200 micromol on basal coronary artery tone were investigated in eight patients with variant angina and normal coronary angiograms and in eight control subjects. The lumen diameters of large epicardial coronary arteries were assessed by quantitative coronary arteriography.

RESULTS

Coronary spasm was provoked by the intracoronary administration of acetylcholine in all patients with variant angina. L-NMMA did not alter the arterial pressure and heart rate but significantly decreased the coronary artery diameter at spastic and nonspastic sites. Constrictive responses to L-NMMA were significantly greater (p < 0.01) at the spastic site (constriction by 200 micromol, 22+/-7%, mean +/- SD) than at the nonspastic site (10+/-7%). Constrictive responses to L-NMMA at the nonspastic site in patients with variant angina were comparable to those in the control subjects.

CONCLUSIONS

These findings support the hypothesis that the basal release of nitric oxide may not be decreased at the spastic site in patients with variant angina.

Angiotensin converting enzyme as a genetic risk factor for coronary artery spasm. Implication in the pathogenesis of myocardial infarction

It has been reported that individuals with the D allele of an insertion/deletion (I/D) polymorphism of the angiotensin converting enzyme (ACE) gene are at greater risk for myocardial infarction (MI), especially among subjects normally considered to be at low risk. However, little is known about the mechanism by which the ACE polymorphism affects the risk of MI. Coronary artery spasm (CAS) is considered to be one possible mechanism for developing MI. We therefore examined the ACE polymorphism relation to CAS to determine if this was the mechanism by which the DD genotype influences MI. We studied 150 angiographically assessed Japanese males, all more than 60 yr old. CASs were detected using intracoronary injection of ergonovine maleate. Subjects were divided into three groups: those with CAS (group 1), those without CAS, but with fixed organic stenosis (group 2); and those without CAS and no organic stenosis (group 3). DD subjects were significantly represented in group 1 when compared with groups 2 (P = 0.002) and 3 (P = 0.026). These results suggest that the DD genotype relates to the greater risk for MI in the patients with CAS.

Bradykinin-induced vasodilation is impaired at the atherosclerotic site but is preserved at the spastic site of human coronary arteries in vivo

BACKGROUND

Bradykinin causes endothelium-dependent vasodilation of isolated human coronary arteries in vitro. However, the effect of bradykinin on vasomotion of human coronary arteries in vivo has not been studied. The aim of this study was to examine whether bradykinin-induced vasodilation is altered at the atherosclerotic or spastic site of human coronary arteries in vivo.

METHODS AND RESULTS

The effect of bradykinin on vasomotion of epicardial coronary arteries was evaluated in 8 patients with normal coronary arteries (control group), 14 patients with organic coronary stenosis (coronary artery disease [CAD] group), and 8 patients with vasospastic angina (VSA group). Changes in the diameter of epicardial coronary artery were assessed by quantitative coronary arteriography. Intracoronary administration of bradykinin at graded doses (60, 200, and 600 ng) dilated epicardial coronary arteries without altering arterial pressure or heart rate in all patients of either group. In the control group, vasomotor responses of the site where acetylcholine caused dilation were compared with the responses of the site where acetylcholine caused constriction. The magnitudes of bradykinin-induced dilation at the site with acetylcholine-induced dilation (mean +/- SD: 6 +/- 6%, 11 +/- 9%, and 15 +/- 9%) were comparable to that (3 +/- 6%, 8 +/- 8%, and 13 +/- 9%) at the site with acetylcholine-induced constriction. In the CAD group, vasomotor responses of the stenotic site (% diameter stenosis, 15% to 50%) and nonstenotic site were examined. The bradykinin-induced dilation at the stenotic site (0 +/- 4%, 3 +/- 8%, and 5 +/- 9%) was significantly less (P < .01) than at the nonstenotic site (3 +/- 4%, 8 +/- 6%, and 16 +/- 11%) and in the control group. Coronary vasodilation with nitrate at the stenotic site (20 +/- 11%) was comparable to that at the nonstenotic site (22 +/- 16%) and in the control group (21 +/- 10%). In the VSA group, vasomotor responses of the site with acetylcholine-induced spasm and the site without spasm were examined. The bradykinin-induced vasodilation at the spastic site (5 +/- 5%, 16 +/- 15%, and 33 +/- 17%) was comparable to that at the nonspastic site (4 +/- 8%, 12 +/- 14%, and 21 +/- 9%). Nitrate-induced dilation was comparable at the spastic site (51 +/- 19%) and the nonspastic site (32 +/- 13%). The ratio of bradykinin-induced vasodilation to nitrate-induced vasodilation at the spastic site was comparable to the control group.

CONCLUSIONS

These results suggest that bradykinin causes vasodilation of human epicardial coronary arteries in vivo and that bradykinin-induced endothelium-dependent vasodilation is impaired at the stenotic site but is preserved at the angiographically normal site where endothelium-dependent vasodilation by acetylcholine is impaired and at the spastic site.

Enhanced insulin response relates to acetylcholine-induced vasoconstriction in vasospastic angina

OBJECTIVES

This study investigated whether insulin response to an oral glucose load correlates to acetylcholine-induced coronary vasoconstriction in subjects with vasospastic angina.

BACKGROUND

It has been suggested that coronary vasospasm is caused by augmented vascular responsiveness possibly exerted by atherosclerosis. Recently, insulin resistance syndrome has been proposed as a major promotor of atherosclerotic disease, potentially enhancing vascular smooth muscular tone.

METHODS

Among subjects with angiographically smooth coronary arteries, we selected 14 subjects with vasospastic angina and 14 age- and gender-matched subjects with atypical chest pain. We compared coronary vasomotor response to acetylcholine infusion, glucose and insulin responses to an oral glucose load (75 g), serum lipid concentrations, obesity, heart rate, blood pressure and smoking habits in both groups.

RESULTS

Fasting serum insulin concentrations and insulin response were higher in subjects with vasospastic angina than in those with atypical chest pain; however, glucose tolerance, obesity, heart rate, blood pressure and smoking habits did not differ between groups. In subjects with vasospastic angina, nearly all coronary segments, except distal segments of the left circumflex coronary artery, were constricted at peak acetylcholine infusion (20 to 100 micrograms), whereas all segments were dilated in subjects with atypical chest pain. Regression analysis for both groups demonstrated a correlation between coronary vasoconstriction and fasting serum insulin concentrations (r = 0.52, p < 0.01), insulin response (r = 0.71, p < 0.001), serum triglyceride concentrations (r = 0.51, p < 0.05) and atherogenic index (r = 0.44, p < 0.05).

CONCLUSIONS

Results show that acetylcholine-induced coronary vasoconstriction in subjects with vasospastic angina correlates with hyperinsulinemia and enhanced insulin response, suggesting insulin resistance syndrome as a feature of vasospastic angina.

Endothelium-dependent hyperpolarization: a role in the control of vascular tone

Endothelial-dependent relaxation of vascular smooth muscle cells evoked by a number of agonists, including cholinomimetics and substance P, is often accompanied by an increase (repolarization and/or hyperpolarization) in the membrane potential. This change in membrane potential appears predominantly to reflect the action of an endothelial-derived hyperpolarizing factor (EDHF), which is distinct from NO (or endothelial-derived relaxing factor), and is discussed in this article by Chris Garland and colleagues. In large conducting arteries, EDHF may provide a secondary system to NO, which assumes primary importance in some disease states such as pulmonary hypertension and atherosclerosis. However, in small resistance arteries (100-300 microns), EDHF appears to be a major determinant of vascular calibre under normal conditions, and may therefore be of primary importance in the regulation of vascular resistance.

Pharmacological reactivity of human epicardial coronary arteries: characterization of relaxation responses to endothelium-derived relaxing factor

1. Human epicardial coronary artery rings, freshly obtained from cardiac transplant patients, were examined for their responses to endothelium-derived relaxing factor (EDRF)-releasing agents. 2. Functional antagonism profoundly influenced relaxation responses in this tissue. Increasing force with concentrations of U46619 above 3 nM (40% of maximum contraction response) resulted in a reduction of the maximum response to four vasorelaxants which relax vascular smooth muscle via different mechanisms: the EDRF-releasing agents, substance P and bradykinin; the endothelium-independent nitro-vasodilator, sodium nitroprusside (SNP); and the beta-adrenoceptor agonist, isoprenaline. 3. Substance P, histamine, bradykinin and the Ca2+ ionophores ionomycin and A23187 all caused concentration- and endothelium-dependent relaxation in vessels pre-contracted with the thromboxane A2-mimetic, U46619 (3 nM) to an active force optimal for relaxation responses. Nifedipine (0.1 microM), added to prevent spontaneous contractions, had no effect or relaxation responses to substance P, bradykinin and histamine. 4. Substance P was the most potent of the EDRF-releasing agents examined and all agents except for bradykinin caused near-maximal relaxation. Bradykinin caused only 46.2% +/- 7.3% relaxation. Responses were abolished when the endothelium was removed and, except for histamine, were not significantly affected by indomethacin (3-10 microM, P > 0.05). Histamine (0.1-10 microM) caused a concentration-dependent contraction of arterial rings without endothelium. 5. The L-arginine analogues NG-nitro-L-arginine (L-NOARG, 0.1 mM) and NG-monomethyl-L-arginine (L-NMMA, 0.1 mM) both caused no further contraction in arteries precontracted with U46619 (3 nM) and were in general, poor inhibitors of responses to EDRF agonists. L-NMMA, but not L-NOARG,caused small but significant decreases in the maximum responses to substance P, bradykinin (18.5 +/- 6.9% and 27.6 +/- 10.9% relaxation with L-NMMA and L-NOARG, respectively), histamine and A23187 (P<0.05). The analogues had no effect on SNP responses.6. In conclusion, EDRF release in human isolated coronary artery is only poorly antagonized by the nitric oxide synthase inhibitors L-NOARG and L-NMMA. These results indicate that either the nitricoxide transduction pathway present in human coronary artery is different from that in other tissues or that another factor(s) (e.g. endothelium-derived hyperpolarizing factor) is also released in response to EDRF-releasing agents and augments the relaxation to nitric oxide.

Substance P potentiates the algogenic effects of intraarterial infusion of adenosine

OBJECTIVES

This study investigated whether substance P potentiates the muscular and cardiac pain caused by the intraarterial infusion of adenosine, an autocoid known to induce muscular and cardiac ischemic-like pain in humans.

BACKGROUND

Substance P is involved in the generation of neurogenic inflammation and causes cutaneous hyperalgesia. Because substance P is present in perivascular nerves it might also cause muscular and cardiac hyperalgesia. To test this hypothesis its effects on adenosine-induced muscular and cardiac pain were investigated in humans.

METHODS

A randomized, crossover study of the algogenic effects of the intrailiac infusion of increasing scalar doses (from 125 to 2,000 micrograms/min) of adenosine or substance P (11.2 pmol/min) for 3 min, followed by the simultaneous infusion of substance P plus the same doses of adenosine, was carried out in nine patients with no evidence of peripheral vascular disease. A similar protocol was carried out by infusing increasing scalar doses of adenosine (from 50 to 800 micrograms/min) or substance P (11.2 pmol/min) for 3 min, followed by the simultaneous infusion of substance P plus the same doses of adenosine, into the left coronary artery of eight patients with angina. Pain severity, assessed by a visual analog scale, is presented as median. The remaining data are presented as mean value +/- 1 SD.

RESULTS

All patients experienced pain during both adenosine and substance P plus adenosine infusion; no patient experienced pain during the infusion of substance P alone. During intrailiac infusion, all patients experienced pain in the right leg that occurred earlier (207 +/- 152 vs. 321 +/- 154 s, p < 0.05) and was greater (47 vs. 30 mm, p < 0.05) during the simultaneous infusion of substance P plus adenosine than during the infusion of adenosine. Similarly, during intracoronary infusion, all patients experienced chest pain that occurred earlier (409 +/- 242 vs. 596 +/- 210 s, p < 0.05) and was greater (51 vs. 33 mm, p < 0.05) during the simultaneous infusion of substance P plus adenosine than during infusion of adenosine. No patient exhibited electrocardiographic signs of ischemia.

CONCLUSIONS

Substance P does not cause muscular or cardiac pain, but it provokes muscular and cardiac hyperalgesia.

Effects of continuous intravenous infusion of isosorbide dinitrate on development of tolerance to vasodilating action in human epicardial coronary arteries

This study was performed to determine the effects of long-term intravenous infusion on the coronary vasodilating actions of continuous intravenous and bolus intracoronary administration of isosorbide dinitrate (ISDN). With quantitative coronary angiography, the coronary diameter and the vasodilating response to intracoronary ISDN (1 mg) at angiographically normal segments were studied before and after intravenous administration of ISDN, 10 to 60 micrograms/min for 1 hour, 2 days, or 5 days. The vasodilating effects of intravenous ISDN were 72% +/- 13%, 65% +/- 21%, and 6% +/- 11% of the response to intracoronary ISDN in the baseline study in each group. Irrespective of the duration of intravenous infusion, subsequent intracoronary ISDN dilated coronary arteries to extent similar to that observed in each baseline study. In conclusion, significant coronary vasodilating effects of intravenous ISDN were observed after a 2-day infusion, whereas tolerance to the vasodilating effects apparently developed within 5 days of infusion. The vasodilating response to bolus intracoronary ISDN was preserved even when the vasodilating effects of intravenous ISDN were no longer present.

Serotonin-induced coronary spasm in a swine model. A minor role of defective endothelium-derived relaxing factor

BACKGROUND

Coronary spasm may be caused by endothelial dysfunction, vascular smooth muscle hyperreactivity, or both. We aimed to determine the relative role of endothelial dysfunction and vascular smooth muscle hyperreactivity in the pathogenesis of coronary artery spasm in the swine model in vivo.

METHODS AND RESULTS

In Göttingen miniature pigs given a high cholesterol diet, a segment of the left coronary artery was denuded and irradiated with x-ray (total, 30 Gy). Three months after endothelial denudation and irradiation, vasomotor responses of the denuded and control sites to agonists were assessed by quantitative arteriography. Serotonin (10 micrograms/kg) provoked coronary spasm at the denuded site (diameter reduction, 79 +/- 6%) associated with ST elevation but not at the nondenuded control site (21 +/- 6%). Intracoronary infusion of N omega-nitro-L-arginine methyl ester (LNNA, an inhibitor of endothelium-derived nitric oxide) of 1 and 3 mg/kg potentiated constriction evoked with serotonin (1, 3, 10 micrograms/kg) at the control site but did not alter it at the denuded site. However, serotonin-induced constriction after LNNA was still less at the control site (31 +/- 3%) than at the denuded site (80 +/- 5%). Endothelium-dependent vasodilation with substance P (0.1, 1, 10 ng/kg), which was inhibited by LNNA, was less (P < .01) at the denuded site than at the control site, whereas vasodilation with the nitrovasodilator SIN-1 (0.1, 1, 10 ng/kg) was comparable between the two sites. Histological study revealed regenerated endothelial cells and intimal thickening at the denuded site.

CONCLUSIONS

The results suggest that the denuded segment of the coronary artery with regenerated endothelium was associated with defective endothelium-dependent vasodilation mediated by nitric oxide and vascular smooth muscle hyperreactivity to serotonin. However, provocation of coronary spasm with serotonin resulted primarily from vascular smooth muscle hyperreactivity but not by defective nitric oxide production in this swine model.

Peptidergic innervation of human epicardial coronary arteries

The peptidergic innervation of proximal (internal diameter, > 0.8 mm) and distal (internal diameter, < 0.8 mm) regions of human epicardial coronary arteries was investigated by means of immunohistochemical, chromatographic, radioimmunological, and in vitro pharmacological techniques. The use of an antiserum to the general neuronal marker protein gene product 9.5 revealed that the proximal part of epicardial arteries possessed a relatively sparse supply of nerve fibers forming a loose network in the adventitia. The perivascular network increased in density as the vessels were followed distally. In both proximal and distal regions, the majority of nerve fibers possessed neuropeptide Y and tyrosine hydroxylase immunoreactivity. Calcitonin gene-related peptide (CGRP)- and substance P-immunoreactive nerve fibers were very sparse in the proximal region of the arteries and increased in number distally. Only a few scattered vasoactive intestinal peptide (VIP)-immunoreactive nerve fibers were detected in both arterial regions. The use of high-performance liquid chromatography and radioimmunoassay revealed that the immunoreactive material present in coronary artery extracts closely resembled synthetic peptides. An in vitro pharmacological method demonstrated that neuropeptide Y elicited no detectable response in either proximal or distal arterial segments. In contrast, CGRP, substance P, and VIP all produced a concentration-dependent relaxation of both arterial regions. CGRP and substance P were stronger and more potent than VIP. CGRP and substance P induced a more potent response in distal compared with proximal regions of the arteries. These results suggest that the peptidergic nerves supplying human large epicardial coronary arteries may be predominantly involved in mediating vasodilation.