Hirofumi Tagawa

Angina pectoris caused by coronary microvascular spasm

BACKGROUND Microvascular angina can occur during exercise and at rest. Reduced vasodilator capacity of the coronary microvessels is implicated as a cause of angina during exercise, but the mechanism of angina at rest is not known. Our aim was to test the hypothesis that primary hyperconstriction (spasm) of coronary microvessels causes myocardial ischaemia at rest. METHODS Acetylcholine induces coronary artery spasm in patients with variant angina. We tested the effects of intracoronary acetylcholine at graded doses in 117 consecutive patients with chest pain (at rest, during exertion, or both) and no flow-limiting (>50%) organic stenosis in the large epicardial coronary arteries. We also assessed the metabolism of myocardial lactate during acetylcholine administration in 36 of the patients by measurement of lactate in paired blood samples from the coronary artery and coronary sinus vein. FINDINGS Of the 117 patients, 63 (54%) had large-artery spasm, 29 (25%) had microvascular spasm, and 25 (21%) had atypical chest pain. The 29 patients with microvascular spasm developed angina-like chest pain, ischaemic electrocardiogram (ECG) changes, or both spontaneously (two patients) or after administration of acetylcholine (27 patients) without spasm of the large epicardial coronary arteries. Testing of paired samples of arterial and coronary sinus venous blood showed that lactate was produced during angina attack in nine of 11 patients with microvascular spasm. There was more women (p<0.01) and fewer coronary risk factors (p<0.01) in patients with microvascular spasm than in those with large-artery spasm. INTERPRETATION Coronary microvascular spasm and resultant myocardial ischaemia may be the cause of chest pain in a subgroup of patients with microvascular angina.

Long-term treatment with eicosapentaenoic acid augments both nitric oxide-mediated and non-nitric oxide-mediated endothelium-dependent forearm vasodilatation in patients with coronary artery disease

Long-term treatment with eicosapentaenoic acid (EPA) is known to improve impaired endothelium-dependent relaxations of atherosclerotic blood vessels in animals and humans. However, it remains to be determined which mechanisms are involved in this beneficial effect of EPA. In this study, we investigated our hypothesis that EPA improves both nitric oxide (NO)-mediated and non-NO-mediated endothelium-dependent vasodilatation in patients with coronary artery disease. The study included eight patients with documented coronary artery disease. The forearm vascular responses to the endothelium-dependent vasodilator acetylcholine and substance P were examined before and after intraarterial infusion of NG-monomethyl-L-arginine (L-NMMA). Same measurements were repeated after the treatment with EPA (1,800 mg/day) for 6 weeks. The long-term treatment with EPA augmented forearm blood-flow response to both acetylcholine and substance P. Furthermore, acute administration of L-NMMA significantly inhibited the EPA-induced augmented response to acetylcholine but not that to substance P. The forearm vascular response to sodium nitroprusside was unchanged by the EPA treatment. These results indicate that long-term treatment with EPA augments both NO-dependent and non-NO-dependent endothelium-dependent forearm vasodilatation in patients with coronary artery disease. Thus the beneficial effects of EPA appear to extend to non-NO-dependent mechanism(s).

Role of myocyte nitric oxide in β-adrenergic hyporesponsiveness in heart failure

Background The positive inotropic response to β-adrenergic stimulation is attenuated at the isolated myocyte level in heart failure. Nitric oxide (NO) has a negative inotropic effect and attenuates the response to isoproterenol. It has been suggested that NO synthesis is increased in failing myocytes. However, the pathophysiological consequences after induction of NO in myocyte contractility are less clear in the setting of heart failure. Methods and Results We examined the effects of an NO synthase (NOS) inhibitor on contractile function in myocytes isolated from 11 dogs with rapid pacing–induced heart failure (ejection fraction, 29±2%) and 8 control dogs (ejection fraction, 74±3%). Sarcomere shortening velocity was measured as an index of contractility under four experimental conditions: at baseline, after adding isoproterenol (ISO; 1 nmol/L), after an NOS inhibitor (Nϖ-nitro-l-arginine methyl ester [L-NAME], 0.1 nmol/L), and after L-NAME plus ISO. L-NAME alone had no effects on basal sarcomere shorteni...

Basal release of nitric oxide is decreased in the coronary circulation in patients with heart failure.

It is unknown whether basal release of endothelium-derived nitric oxide in the coronary artery is altered in heart failure in humans. The aim of the present study was to evaluate the effect of inhibition of nitric oxide synthesis on basal tone of the conduit and resistance coronary arteries in awake patients. Coronary blood flow velocity (Doppler guide wire) and coronary arterial diameter (quantitative coronary angiography) were measured in 14 patients with heart failure caused by nonischemic left ventricular dysfunction (7 idiopathic dilated cardiomyopathy and 7 valvular insufficiency) and 7 patients with normal ventricular function (controls). Intracoronary N(G)-monomethyl-L-arginine (L-NMMA), an inhibitor of nitric oxide synthesis, at graded doses decreased coronary blood flow in both groups. However, the magnitude of flow reduction was smaller in patients with heart failure than in control patients (P<.0001). The magnitude of coronary blood flow reduction in response to L-NMMA inversely correlated to indexes of left ventricular contractile function (P<.01) but was not affected by the cause of heart failure. Constriction of the large epicardial coronary artery with L-NMMA also tended to be attenuated in patients with heart failure. In summary, vasoconstricting response to L-NMMA was blunted in the coronary resistance artery in heart failure in vivo. These findings suggest that basal release of nitric oxide in the coronary circulation is decreased in patients with heart failure.

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).

Regulation of Fibrillar Collagen Gene Expression and Protein Accumulation in Volume-Overloaded Cardiac Hypertrophy

BACKGROUND Interstitial collagen accumulation has been extensively demonstrated to be increased at both mRNA and protein levels in pressure-overloaded cardiac hypertrophy. However, few data are available regarding the effects of volume overload on myocardial collagens. METHODS AND RESULTS To determine whether the alterations of collagens may occur in volume-overloaded cardiac hypertrophy, we measured collagen types I and III mRNA levels and protein accumulation in left ventricular (LV) myocardium of rats at 3, 7, and 28 days after the creation of an aortocaval (AC) shunt. Eccentric LV hypertrophy was produced in rats with AC shunting. Northern blot analysis on RNA extracted from LV tissue indicated that the steady state mRNA levels for both type I and III collagen were persistently upregulated in AC shunt rats compared with sham-operated operated control rats. In contrast, the biochemical collagen protein concentration and morphometric collagen volume fraction were comparable between sham-operated control and AC shunt rats at any study time point. Furthermore, the immunohistochemical staining of types I and III collagen and Sirius red staining on myocardial tissue sections revealed no significant alterations in the distribution or density of fibrillar collagens in AC shunt rats. Tissue collagenase activity was not different between control and AC shunt rats after 28 days. CONCLUSIONS Cardiac volume overload increases LV collagen mRNA as does pressure overload. However, in contrast to pressure-overloaded hypertrophy, the upregulation of collagen transcriptional activity does not result in subsequent myocardial fibrosis in volume-overloaded hypertrophy due to AC shunting. Therefore, the upregulation of collagen gene expression and protein accumulation might be different in pressure-overloaded and volume overloaded hypertrophy.

Basis for Increased Microtubules in Pressure-Hypertrophied Cardiocytes

BACKGROUND We have shown the levels of the sarcomere and the cardiocyte that a persistent increase in microtubule density accounts to a remarkable degree for the contractile dysfunction seen in pressure-overload right ventricular hypertrophy. In the present study, we have asked whether these linked phenotypic and contractile abnormalities are an immediate and direct effect of load input into the cardiocyte or instead a concomitant of hypertrophic growth in response to pressure overloading. METHODS AND RESULTS The feline right ventricle was pressure-overloaded by pulmonary artery banding. The quantity of microtubules was estimated from immunoblots and immunofluorescent micrographs, and their mechanical effects were assessed by measuring sarcomere motion during microtubule depolymerization. The biogenesis of microtubules was estimated from Northern and Western blot analyses of tubulin mRNAs and proteins. These measurements were made in control cats and in operated cats during and after the completion of right ventricular hypertrophy; the left ventricle from each heart served as a normally loaded same-animal control. We have shown that the alterations in microtubule density and sarcomere mechanics are not an immediate consequence of pressure overloading but instead appear in parallel with the load-induced increase in cardiac mass. Of potential mechanistic importance, both these changes and increases in tubulin poly A+ mRNA and protein coexist indefinitely after a new, higher steady state of right ventricular mass is reached. CONCLUSIONS Because we find persistent increases both in microtubules and in their biosynthetic precursors in pressure-hypertrophied myocardium, the mechanisms for this cytoskeletal abnormality must be sought through studies of the control both of microtubule stability and of tubulin synthesis.

Role of coronary artery spasm in progression of organic coronary stenosis and acute myocardial infarction in a swine model. Importance of mode of onset and duration of coronary artery spasm.

BackgroundCoronary spasm may play an important role in progression of organic coronary stenosis and myocardial infarction, but the mechanisms responsible for these complications are not known. This study aimed to examine whether the mode of onset and the duration of coronary spasm influenced progression of organic coronary stenosis and acute myocardial infarction in a swine model of coronary spasm. Methods and ResultsGottingen miniature pigs were subjected to cholesterol feeding, balloon-induced coronary arterial denudation, and x-ray irradiation. Five months later, coronary spasm was induced by intracoronary injection of serotonin. In 10 pigs, coronary spasm was provoked abruptly and maintained for 25 minutes by five repeated intracoronary injections of serotonin (10 μg/kg) every 5 minutes (group A, abrupt onset and short duration). In group B, coronary spasm was provoked gradually by intracoronary injections of serotonin at graded doses of 0.1, 0.3, and 0.6 μg/kg every 5 minutes and was then maintained for 25 minutes in four pigs (group BR, gradual onset and short duration) and for 120 minutes in six pigs (group B2, gradual onset and long duration) by repeated intracoronary injections of serotonin (10 μg/kg) every 5 minutes. Intramural hemorrhage was noted histologically at the spastic site more frequently in group A with abrupt onset (nine of 10 pigs) than in group B with gradual onset (two of 10 pigs) (p<0.01). Progression of organic coronary stenosis due to intramural hemorrhage was noted in seven pigs (six pigs in group A and one pig in group B), including three cases of total coronary occlusion. Evidence for the evolution of acute myocardial infarction (serial ECG findings, left ventriculograms, and histological findings) was noted in one pig (7%) of group A or B1 with short duration and in five of six pigs (83%) in group B2 with long duration (p<0.01 versus group A and Bi). ConclusionThese results indicate that 1) intramural hemorrhage was frequently induced by coronary spasm of abrupt but not of gradual onset, 2) intramural hemorrhage resulted in acute progression of coronary stenosis and sometimes resulted in persistent total coronary occlusion leading to acute myocardial infarction, and 3) prolonged coronary spasm resulted in acute myocardial infarction without progression of organic coronary stenosis.

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.

Role of SR Ca2+-ATPase in contractile dysfunction of myocytes in tachycardia-induced heart failure.

Sarcoplasmic reticulum (SR) Ca2+-ATPase gene expression is reduced in the failing myocardium. However, the functional relevance of these changes to myocardial contractility is not yet established. We assessed myocardial contractile function by analyzing sarcomere motion of isolated myocytes and also quantified SR Ca2+ regulatory protein gene expression by Northern blot analysis in the same hearts obtained from 10 dogs with pacing-induced heart failure (HF; 240 beats/min, 4 wk) and 7 control dogs. Sarcomere-shortening velocity was depressed in HF myocytes, accompanied by the prolongation of intracellular Ca2+ concentration ([Ca2+]i) transient measured by indo 1 fluorescence ratio. SR Ca2+-ATPase mRNA levels (normalized to glyceraldehyde-3-phosphate dehydrogenase mRNA) were significantly depressed in HF, and calsequestrin mRNA was increased. For control and HF dogs, sarcomere-shortening velocity correlated positively with Ca2+-ATPase mRNA levels ( r = 0.73, n = 17, P < 0.01) but not with calsequestrin mRNA. Ca2+-ATPase mRNA levels were correlated with45Ca2+uptake rate by SR, which was also reduced in HF. Moreover, the inhibition of SR Ca2+-ATPase with thapsigargin or cyclopiazonic acid reproduced in normal myocytes the abnormalities observed in HF myocytes, such as depressed contractility and the prolonged [Ca2+]itransient duration. A downregulation of Ca2+-ATPase gene expression and a resultant decrease in Ca2+ uptake by SR may be responsible for the contractile dysfunction and the alterations of [Ca2+]itransient in HF.