Takeshi Kuga

Effects of l-Arginine Supplementation on Endothelium-Dependent Coronary Vasodilation in Patients With Angina Pectoris and Normal Coronary Arteriograms

BACKGROUND The pathogenesis of impaired endothelium-dependent coronary vasodilation in angina pectoris and normal coronary arteriograms (microvascular angina pectoris) is not known. We examined whether supplementation with L-arginine, a precursor of endothelium-derived nitric oxide, improves endothelium-dependent coronary vasodilation in patients with microvascular angina. METHODS AND RESULTS The effect of intracoronary infusion of L-arginine (50 mg/mm) on acetylcholine-induced coronary vasomotion was studied in eight patients with microvascular angina and eight control subjects. The responses of the large epicardial coronary artery diameter and coronary blood flow were measured with coronary arteriography and an intracoronary Doppler catheter, respectively. Acetylcholine increased coronary blood flow with modest vasoconstriction of the large coronary artery without altering arterial pressure and heart rate. The acetylcholine-induced increases in coronary blood flow were significantly less (P < .01) in patients than in control subjects. L-Arginine significantly augmented the coronary blood flow responses to acetylcholine in patients, but not in control subjects. L-Arginine did not alter responses of the large coronary artery in either group. CONCLUSIONS Study results suggest that L-arginine improved endothelium-dependent vasodilation of coronary microcirculation in patients with microvascular angina pectoris.

Cell Cycle-Dependent Expression of L- and T-Type Ca2+ Currents in Rat Aortic Smooth Muscle Cells in Primary Culture

The expression of L- and T-type Ca2+ channels has been reported to change during various biological events, including cellular differentiation and proliferation. The present study aimed to examine whether or not the expression of L- and T-type Ca2+ channels depends on the cell cycle in rat aortic smooth muscle cells in primary culture. Both the phase of the cell cycle and the functional expression of Ca2+ channels were determined in the same single cell, using an immunocytochemical analysis of cell cycle-specific nuclear antigens and a whole-cell voltage-clamp method, respectively. In the G0 (n = 130) and M (n = 75) phases, all cells showed only L-type Ca2+ currents. The cells showing a T-type Ca2+ current appeared in the G1 phase (37%, n = 85) and increased in the S phase (90%, n = 21). For L-type Ca2+ channels, the current density was significantly greater in the G1 phase than in the G0 and M phases. However, either the voltage-dependent properties or the dose-response relationships of Bay K 8644- and second messenger-induced modulations of L-type Ca2+ current did not differ in the four phases of the cell cycle. These findings thus indicate that the expression of L- and T-type Ca2+ channels depends on the cell cycle, whereas the characteristics of L-type Ca2+ channels do not differ between the phases of the cell cycle.

Low‐voltage‐activated calcium current in rat aorta smooth muscle cells in primary culture.

1. Electrical and pharmacological properties of the low‐voltage‐activated Ca2+ current (ICa, LVA) in rat aorta smooth muscle cells (SMC) in primary culture were examined, particularly in comparison with the high‐voltage‐activated Ca2+ current (ICa, HVA). Both types of Ca2+ currents were recorded in external solution containing 20 mM‐Ca2+, using the whole‐cell voltage‐clamp technique. 2. ICa, LVA was evoked by step depolarizations to potentials more positive than ‐60 mV from a holding potential of ‐100 mV, and reached a peak in the current‐voltage (I‐V) relationship around ‐30 mV. ICa, HVA was activated at ‐20 mV, and reached a peak at +20 mV. 3. The intracellular dialysis of 5 mM‐F‐ irreversibly suppressed ICa, HVA, with time, while it has little effect on the ICa, LVA. The ICa, LVA could be separated from the ICa, HVA by either selecting the holding and test potential levels or by perfusing intracellularly with F‐. 4. The ratio of peak amplitude of Ba2+, Sr2+ and Ca2+ currents in the respective I‐V relationship was 1.6:1.2:1.0 for high‐voltage‐activated Ca2+ channels and was 1.0:1.4:1.0 for low‐voltage‐activated ones. 5. The inactivation phase of ICa, HVA was fitted by a sum of double‐exponential functions, the time constants of which were larger when the current was carried by Ba2+ than by Ca2+. The inactivation time course of ICa, LVA was fitted by a single‐exponential function, and the time constant was practically the same when the current was carried by Ba2+ or by Ca2+. Activation and inactivation processes of ICa, LVA were potential‐dependent. 6. The steady‐state inactivation curve of ICa, LVA was fitted by the Boltzmann equation, having a mid‐potential of ‐80 mV and a slope factor of 5.0. The recovery time course from steady‐state inactivation was fitted by a sum of two exponential functions. The time constants of the faster phase were 230 and 380 ms, and those of slower phase were 2.8 and 1.8 s at the repolarization potentials of ‐120 and ‐100 mV, respectively. 7. The amplitude of ICa, LVA depended on the external Ca2+ concentration ([Ca2+]o), approaching saturation at 95 mM [Ca2+]o. 8. Various polyvalent cations blocked both types of Ca2+ current reversibly in the order (IC50 in M): La3+ (8 x 10(‐8)) greater than Cd2+ (6 x 10(‐6)) greater than Ni2+ (1 x 10(‐5)) greater than Zn2+ (2 x 10(‐5)) for ICa, HVA, and La3+ (6 x 10(‐7)) greater than Zn2+ (3 x 10(‐5)) greater than Cd2+ (4 x 10(‐4)) greater than Ni2+ (6 x 10(‐4)) for ICa, LVA.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

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.

Role of Endothelium-Derived Nitric Oxide in Coronary Vasodilatation Induced by Pacing Tachycardia in Humans

Endothelium-derived NO contributes to the control of coronary perfusion. We investigated the roles of NO in the metabolic coronary vasodilatation induced by rapid pacing in humans. We evaluated the dilatation of large epicardial and resistance coronary arteries during rapid atrial pacing before and after intracoronary infusion of NG-monomethyl-L-arginine (L-NMMA), an inhibitor of NO synthesis, in 19 patients without significant coronary artery disease. The diameter of the large epicardial coronary artery and coronary blood flow (CBF) were assessed by quantitative coronary arteriography and by a Doppler flow velocity measurement. An increase in the heart rate increased CBF (P < .01) and the coronary artery diameter (P < .05). L-NMMA at a total dose of 200 mumol reduced basal CBF but did not significantly affect basal coronary artery diameter, arterial pressure, or heart rate. L-NMMA inhibited the pacing-induced dilatation of the large coronary arteries (P < .05) but did not affect pacing-induced increases in CBF. L-NMMA inhibited the acetylcholine-induced increase in CBF (P < .01) and acetylcholine-induced dilatation of the large epicardial coronary artery (P < .05). These results show that the contribution of NO to the metabolic vasodilatation during rapid pacing may differ between large epicardial and resistance coronary arteries in patients without significant coronary artery disease.

Bradykinin-Induced Vasodilation of Human Coronary Arteries In Vivo: Role of Nitric Oxide and Angiotensin-Converting Enzyme

OBJECTIVES The present study aimed to determine the role of nitric oxide (NO) and angiotensin-converting enzyme (ACE) in bradykinin (BK)-induced dilation of human coronary arteries in vivo. BACKGROUND BK, produced by way of the kinin-kallikrein system, causes endothelium-dependent vasodilation. However, little is known about the mechanism of BK-induced dilation of coronary arteries in humans in vivo. METHODS The effects of an inhibitor of NO synthesis and of an ACE inhibitor on BK-induced coronary vasodilation were examined in 20 patients who had no significant atherosclerotic stenosis in the artery under study. Lumen diameters of the large epicardial coronary arteries and coronary blood flow (CBF) were measured by quantitative coronary arteriography and intracoronary Doppler technique. RESULTS Intracoronary infusion of BK (0.6 and 2.0 micrograms/min) increased coronary artery diameter and CBF with no change in arterial pressure or heart rate. The BK-induced increases in coronary artery diameter and CBF were significantly reduced (p < 0.01) after pretreatment with NG-monomethyl-L-arginine (200 mumol) and were significantly increased (p < 0.01) after pretreatment with enalaprilat (50 micrograms). CONCLUSIONS BK-induced dilation of human large epicardial and resistance coronary arteries is mediated by NO and increased by prior ACE inhibition.

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.

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.

Altered Serotonin Receptor Subtypes Mediate Coronary Microvascular Hyperreactivityin Pigs With Chronic Inhibitionof Nitric Oxide Synthesis

BACKGROUND We previously reported that chronic inhibition of nitric oxide synthesis by administration of N omega-nitro-L-arginine methyl ester (L-NAME) causes microvascular hyperreactivity to 5-hydroxytryptamine (5-HT) and vascular structural changes in pigs in vivo. In the present study, we investigated the relative contributions of 5-HT receptor subtypes to microvascular hyper-reactivity in this animal model. METHODS AND RESULTS Coronary vasomotor response was studied in 16 pigs treated with oral L-NAME for 4 weeks (L group) and in 11 control pigs (C group). Intracoronary administration of 5-HT at 30 micrograms/kg decreased coronary blood flow (CBF) in the two groups. The decrease in CBF by 5-HT was greater (P < .01) in the L group than in the C group. The decrease in CBF by 5-HT in the C group was blocked completely by pretreatment with ketanserin, a 5-HT2 antagonist. In contrast, the augmented decrease in CBF by 5-HT in the L group was only partly inhibited by ketanserin alone and was blocked completely by ketanserin and methiothepin, a 5-HT1/5-HT2 antagonist. The decrease in CBF caused by prostaglandin F2 alpha and the increase in CBF caused by nitroglycerin were comparable between the two groups and were not affected by the 5-HT antagonists. CONCLUSIONS These results suggest that the 5-HT-induced microvascular hyperreactivity may be mediated by relative changes in affinity for 5-HT receptors or de novo expression of 5-HT1 receptors in microvascular smooth muscle cells in our animal model.