Relationship between normalization of negative T waves on exercise ECG and residual myocardial viability in patients with previous myocardial infarction and no post-infarction angina

The usefulness of normalization of negative T waves in exercise ECG was investigated as an index of myocardial viability in patients with previous myocardial infarction with no symptoms or ischemic ST-segment change during exercise test. A total of 39 patients, 20 with T-wave normalization (POS group) and 19 without T-wave normalization (NEG group) on exercise ECG. were studied. Myocardial viability was evaluated by thallium-201 single-photon emission computed tomography (SPECT) during exercise or at rest. We also assessed left ventricular ejection fraction (LVEF) by contrast ventriculography before (n=39) and after percutaneous transluminal coronary angioplasty (PTCA) (n=17). SPECT detected myocardial viability in 16 (80%) of the 20 patients in the POS group and in 4 (21%) of the 19 patients in the NEG group (p<0.01). LVEF increased after successful PTCA in the POS group (from 53+/-13% to 63+/-8%, p<0.025), but fell in the NEG group (from 57+/-10% to 51+/-8%). It is concluded that normalization of negative T waves on exercise ECG is a useful, simple index of myocardial viability in patients with previous myocardial infarction with no symptoms or ischemic ST-segment change during exercise testing.

Methylenetetrahydrofolate reductase and apolipoprotein E polymorphisms are independent risk factors for coronary heart disease in Japanese: a case-control study

A missense variant of the C677T (Ala --> Val) polymorphism in the methylenetetrahydrofolate reductase gene (MTHFR) (the T allele) may increase levels of plasma homocysteine. Apolipoprotein E4 increases plasma LDL-cholesterol levels. Increased levels of homocysteine and LDL-cholesterol have been recognized as risk factors for coronary heart disease (CHD). To examine whether the polymorphisms in the MTHFR gene and the APOE gene are associated with CHD in the Japanese, we analyzed 214 CHD patients with an onset age before 65 and 310 apparently healthy persons. In the controls, significantly higher plasma concentrations of homocysteine were observed in the MTHFR TT genotype (15.1+/-6.0 mmol/l) compared with the CT genotype (11.2+/-1.9 mmol/l) and the CC genotype (10.5+/-3.3 mmol/l). The MTHFR TT genotype was significantly more frequent in the CHD patients (28.5%) compared with the control subjects (13.5%); the odds ratio was 2.54 (P < 0.00003). Subjects with the apo E4 allele were significantly more frequent in the CHD group (22.9%) than in the control group (10.0%); the odds ratio was 2.74 (P < 0.00004). Multivariate analysis showed that the TT genotype of MTHFR and the apoE4 allele are independent risk factors for CHD in the Japanese.

[The results of questionnaire on quantitative assessment of 123I-metaiodobenzylguanidine myocardial scintigraphy in heart failure]

This study was done by working group under the cooperation between Japanese Society of Nuclear Medicine and Japanese Circulation Society. We evaluated the usefulness of quantitative assessment of 123I-metaiodobenzylguanidine (MIBG) myocardial scintigraphy in heart failure by the results of questionnaire. Forty-nine (72.1%) of 68 selected institutions participated in this study. The incidence of MIBG myocardial scintigraphy used in heart failure was 41.1%. The imaging protocol was mostly done by both planar and SPECT at 15 min and 3.6 hr after intravenous injection of 111 MBq of MIBG. The quantitative assessment was mostly done by heart/mediastinum (H/M) ratio and washout rate analysis based on planar imaging. The mean normal value of H/M ratio were 2.34 +/- 0.36, and 2.49 +/- 0.40, at early and delayed images, respectively. The normal value of washout rate was 27.74 +/- 5.34%. On the other hand, those of H/M ratio in heart failure were 1.87 +/- 0.27, and 1.75 +/- 0.24, at early and delayed images, respectively. That of washout rate was 42.30 +/- 6.75%. These parameters were very useful for the evaluation of heart failure. In conclusion, MIBG myocardial scintigraphy was widely used for not only early detection and severity assessment, but also indication for therapy and prognosis evaluation in heart failure patients.

Long-term evaluation of combined antihypertensive therapy with lisinopril and a thiazide diuretic in patients with essential hypertension

For the treatment of hypertension, the combination of an angiotensin-converting enzyme (ACE) inhibitor and a thiazide diuretic is supported by multiple lines of evidence, because these drugs have synergistic action and are expected to cancel out each other's adverse side effects. However, the long-term outcome of this combination antihypertensive therapy is not entirely clear. In the present multicenter open trial, we investigated the long-term efficacy and safety of combined antihypertensive therapy with an ACE inhibitor, lisinopril, and a thiazide diuretic, trichlormethiazide. A total of 466 patients with essential hypertension were treated with lisinopril alone (monotherapy group, n = 360) or with a combination of lisinopril with trichlormethiazide (combination therapy group, n = 106) for 1 year. The average blood pressure was effectively lowered to below 150/90 mmHg in both the monotherapy and the combination therapy groups throughout the study period. The average maintenance dose of lisinopril was lower when combined with thiazide than when given alone (9.8 vs. 11.5 mg/day, p < 0.001). Dry cough was the major side effect of lisinopril; no severe adverse effects were observed. The incidence of cough was not significantly different between the monotherapy group (13.1%) and the combination therapy group (11.3%). The increase in serum potassium observed in the monotherapy group was reversed by the concurrent use of the thiazide diuretic in the combination therapy group. Fasting blood glucose was significantly reduced in the monotherapy group; the reduction observed in the combination therapy group was not significant. Thus, the present results provide useful information as to the effectiveness and safety of combined antihypertensive therapy with lisinopril and a thiazide in comparison with monotherapy with lisinopril.

Randomized, double-blind, placebo-controlled study of supplemental vitamin E on attenuation of the development of nitrate tolerance

BACKGROUND

The attenuation of intracellular production of cGMP has been known to be a mechanism of nitrate tolerance. A recent in vitro study showed an increase in superoxide levels and a reduced activation of guanylate cyclase in tolerant vessels. We investigated the preventive effect of an antioxidant, vitamin E, on the development of nitrate tolerance.

METHODS AND RESULTS

In this double-blind, placebo-controlled study, 24 normal volunteers and 24 patients with ischemic heart disease (IHD patients) were randomized to receive either vitamin E (200 mg TID vitamin E group) or placebo (placebo group). Vasodilator response to nitroglycerin was assessed with forearm plethysmography by measurement of the change in the forearm blood flow before and 5 minutes after sublingual administration of 0.3 mg nitroglycerin, and at the same time, blood samples were taken from veins to measure the platelet cGMP level. Measurements of the forearm blood flow and blood sampling were obtained serially at baseline (day 0), 3 days after vitamin E or placebo alone was taken (day 3), and 3 days after application of a 10-mg/24-h nitroglycerin tape concomitantly with oral vitamin E or placebo (day 6). The responses of forearm blood flow (%FBF) and cGMP (%cGMP) after sublingual nitroglycerin on day 0 (%FBF: normal volunteers, 32+/-12 versus 31+/-11; IHD patients, 35+/-15 versus 34+/-15; %cGMP: normal volunteers, 38+/-10 versus 35+/-11; IHD patients, 37+/-11 versus 38+/-12, vitamin E group versus placebo group) and day 3 (%FBF: normal volunteers, 33+/-9 versus 32+/-12; IHD patients, 35+/-12 versus 33+/-13; %cGMP: normal volunteers, 38+/-10 versus 37+/-11; IHD patients, 36+/-14 versus 37+/-10, vitamin E group versus placebo group) were not different between the two groups. On day 6, %FBF and %cGMP in the placebo group were significantly lower compared with day 0, and there were significant differences in them between the two groups (%FBF: normal volunteers, 30+/-12 versus 17+/-9, P<.01; IHD patients, 28+/-14 versus 17+/-8, P<.01; %cGMP: normal volunteers, 35+/-11 versus 8+/-5, P<.01; IHD patients, 38+/-10 versus 12+/-4, P<.01, vitamin E group versus placebo group).

CONCLUSIONS

These results indicate that the combination therapy with vitamin E is potentially a useful method to prevent the development of nitrate tolerance.

Effects of enalapril during continuous nitrate therapy: analysis of diameter of coronary arteries and platelet cyclic guanosine monophosphate

To investigate the effects of enalapril, an angiotensin-converting enzyme inhibitor, on nitrate tolerance during continuous nitrate therapy, coronary artery diameters and platelet cyclic guanosine monophosphate (cGMP) levels were measured before and 2 minutes after intracoronary injection of nitroglycerin 200 microg in 60 patients with coronary artery disease and were compared among 20 patients treated with nitrates (nitrate group), 20 patients treated with both nitrates and enalapril (enalapril group), and 20 untreated patients (control group). The percent increase in platelet cGMP and coronary dilatation in the nitrate group was significantly less than in the control group, but the percent increase in the enalapril group was significantly greater than that in the nitrate group. These results indicate that enalapril may be helpful as concomitant therapy to maintain the effect of nitrates during continuous nitrate therapy.

[Typical normal cases and normal cases with abnormal image pattern in every myocardial SPECT radiopharmaceutical]

Working group of cardiac nuclear medicine was made as a Japanese part of society of international cardiac nuclear medicine under the cooperation between Japanese society of nuclear medicine and Japanese society of cardiology. We investigated typical normal cases and normal cases with abnormal image pattern in every myocardial SPECT radiopharmaceutical as one of the research activity of working group. From 11 faculties, 16 T1 cases, 14 BMIPP cases, 8 MIBG cases, 8 MIBI cases and 14 tetrofosmin cases were submitted as typical normal cases, and 12 T1 cases, 5 BMIPP cases, 12 MIBG cases, 10 MIBI cases and 5 tetrofosmin cases were submitted as normal cases with abnormal image pattern. We summarized the condition of SPECT data acquisition of each faculties. And we added the discussion from literature about how to discriminate normal cases with abnormal image pattern from abnormal cases. In MIBG, patterns of typical normal cases and normal cases with abnormal image pattern were slightly different from other 4 pharmaceuticals. In other 4 pharmaceuticals, diaphragmatic attenuation, breast attenuation, apical thinning and others were presented as normal cases with abnormal image pattern.

Dynamic intravenous coronary arteriography using synchrotron radiation and its application to the measurement of coronary blood flow

We have developed dynamic intravenous coronary arteriography (IVCAG) using a monochromatic (33.3 keV), 2-dimensional X-ray beam (70 x 70 mm) generated from synchrotron radiation. To investigate its use to visualize the coronary arteries and to estimate coronary blood flow, we performed IVCAG in 10 dogs and 1 goat. The animals were irradiated with the synchrotron beam after intravenous injection of a contrast agent, and images were obtained using a TV camera and videorecorder. In the dogs, blood flow in the left anterior descending coronary artery (LAD) was also estimated from the images by applying a transit-time analysis. We obtained dynamic IVCAG images in the dogs and goat and could visualize even a deliberately created coronary stenosis about 1 mm in length. In addition, coronary blood flow could be estimated with an acceptable degree of accuracy. LAD flow calculated from IVCAG was 14.7 +/- 5.1 ml/min, whereas measured LAD flow was 16.6 +/- 4.8 ml/min. There was a close correlation between the estimated and measured LAD flows (r = 0.90, p < 0.01). Thus, dynamic IVCAG is minimally invasive, permits the simultaneous evaluation of coronary anatomy and blood flow, and may be feasible for clinical application.

Relation of a decrease in arterial compliance to ST segment depression on exercise electrocardiograms in patients with hypertension

Decreased arterial compliance (ACo) and increased arterial resistance are the major alterations of arterial function in patients with hypertension. The influence of decreased ACo on the heart was investigated in patients with hypertension. Patients with a systolic blood pressure of > 140 mmHg, a diastolic blood pressure of > 90 mmHg, or both, who had normal coronary arteriograms were enrolled. These patients were divided into two groups according to the value of ACo: Group I, patients with ACo > or = 0.9 ml/mmHg (n = 15); and Group II, patients with ACo < 0.9 ml/mmHg (n = 13). There were no significant differences in arterial resistance, age, gender, and body surface area between the groups. Echocardiographic, hemodynamic, and exercise stress test variables were compared between the groups. There were no differences between the groups in left ventricular (LV) wall thickness and volume, cardiac output, LV end-diastolic pressure, and LV ejection fraction. However, pulse pressure was higher in Group II than in Group I. Ergometer exercise stress testing revealed that, although exercise duration and the peak rate-pressure product were similar in the two groups, ST segment depression of > or = 1.0 mm on the exercise electrocardiograms was induced more frequently in Group II than in Group I (92% vs. 27%, p < 0.001). Thus, the decrease in ACo in patients with hypertension may not significantly affect LV wall thickness, volume, or ejection fraction; however, it may increase pulse pressure and may adversely affect coronary circulation, as suggested by the ST segment depression on exercise electrocardiograms.

Pregnancy increases ET-1-induced contraction and changes receptor subtypes in uterine smooth muscle in humans

The purpose of the present study was to investigate whether pregnancy affects endothelin (ET)-1-induced contraction, the density ofET receptors, and the ratio of receptor subtypes (ET(A) and ET(B)) in uterine smooth muscle in humans. We also investigated which ET receptor subtypes mediate ET-1-induced contraction in the human uterus. In uterine membrane preparations, (125)I-labeled ET-1 ((125)I-ET-1) binding sites (Bmax) in pregnant women did not differ from those in age-matched nonpregnant women (596.2 +/- 107.1 vs. 512.1 +/- 167.7 fmol/mg protein). The dissociation constant (Kd) in pregnant women did not differ from that in nonpregnant women. Competitive displacement experiments with (125)I-ET-1 binding to the membranes using BQ-123 (ET(A) receptor antagonist) showed that the percentage of ET(A) receptors in uterine muscle was significantly higher in pregnant women than in nonpregnant women (P < 0.01). The calculated ratios of ET(A) to ET(B) receptors in pregnant and nonpregnant uteri were 92:8 and 68:32, respectively. Combination treatment with BQ-788 (ET(B) receptor antagonist) completely inhibited the BQ-123-resistant component of (125)I-ET-1 specific binding. ET-1 caused dose-dependent contractions in isolated human uteri from both pregnant and nonpregnant women. The maximum response was markedly greater in pregnant women than in nonpregnant women, whereas pD2 (-log[EC50]) values did not differ between pregnant and nonpregnant uteri. In pregnant human uterus, BQ-123 (10(-6) M) significantly shifted the dose-dependent curve of ET-1 response to the right, whereas BQ-3020 (ET(B) receptor agonist) did not cause contraction. These results suggested that ET-1-induced contraction of the human uterus is mediated through only ET(A) receptors and that ET-1-induced uterine contraction in humans is markedly increased during pregnancy. In addition, the present study suggests that, although (125)I-ET-1 Bmax are not altered during pregnancy, the proportion of ET(A) receptors is increased and that of ET(B) receptors is decreased in the pregnant human uterus.

Inhibition of myocardial endothelin pathway improves long-term survival in heart failure

Occlusion of the diseased coronary artery in humans causes acute myocardial infarction, survivors of which have a high risk for the development of chronic heart failure. Cardiac myocytes and vascular endothelial cells produce endothelin-1 (refs 2-4), which increases the contractility of cardiac muscle and of vascular smooth muscle cells. Endothelin-1 also exerts long-term effects such as myocardial hypertrophy, and causes cellular injury in cardiac myocytes. Production of endothelin-1 is markedly increased in the myocardium of rats with heart failure, and acute application of an endothelin-receptor antagonist decreases myocardial contractility in such rats, indicating that myocardial endothelin-1 may help to support contractility of the failing heart. But we report here that the upregulated myocardial endothelin system may contribute to the progression of chronic heart failure, because long-term treatment with an endothelin-receptor antagonist greatly improved the survival of rats with chronic heart failure. This beneficial effect was accompanied by significant amelioration of left ventricular dysfunction and prevention of ventricular remodelling, in which there is usually an increase in the ventricular mass and cavity enlargement of the ventricle.

Pulmonary hypertension caused by congestive heart failure is ameliorated by long-term application of an endothelin receptor antagonist. Increased expression of endothelin-1 messenger ribonucleic acid and endothelin-1-like immunoreactivity in the lung in congestive heart failure in rats

OBJECTIVES

The purpose of this study was to investigate whether 1) endothelin-1, a potent vasoconstrictor peptide, is involved in progression of pulmonary hypertension caused by congestive heart failure (CHF); and 2) whether long-term treatment with BQ-123, an endothelin receptor antagonist, ameliorates pulmonary hypertension caused by CHF.

BACKGROUND

Congestive heart failure accompanies pulmonary hypertension, and the severity of pulmonary hypertension is an important determinant of prognosis. Although we reported that production of endothelin-1 is increased in the failing heart in rats with CHF, it is not known whether production of endothelin-1 in the lung is altered by CHF.

METHODS

Congestive heart failure was induced by coronary artery ligation in rats. Expression of preproendothelin-1 messenger ribonucleic acid (mRNA) in the lung and kidney was determined. Endothelin-1 staining (immunoreactivity) in the lung was studied by immunohistochemical analysis. Effects of long-term BQ-123 treatment on the rats were studied.

RESULTS

Two weeks postoperatively, CHF accompanied by pulmonary hypertension developed in the rats (CHF rats). Expression of preproendothelin-1 mRNA in the lung was markedly higher in the CHF rats than in the sham-operated rats, whereas that in the kidney did not differ between the two groups. Endothelin-1 staining on the pulmonary vascular endothelial cells was more intense in the CHF rats. BQ-123 treatment over a 2-week period in the CHF rats greatly reduced right ventricular systolic pressure and central venous pressure, but it did not affect blood pressure or left ventricular contractility (peak positive first derivative of left ventricular pressure) in these rats.

CONCLUSIONS

Long-term BQ-123 treatment greatly ameliorated pulmonary hypertension in the CHF rats. The present study suggests that endothelin-1 plays an important role in the progression of pulmonary hypertension caused by CHF and that an endothelin receptor antagonist may be a new therapeutic agent for CHF-induced pulmonary hypertension.

Alterations in left ventricular wall stress and coronary circulation in patients with isolated systolic hypertension

OBJECTIVES

To study the alterations in cardiac function and coronary circulation in patients with isolated systolic hypertension (ISH).

PATIENTS

Ten patients with a history of ISH were studied and findings were compared with those of seven normotensive subjects. All of the patients had angiographically normal coronary arteries. They underwent cardiac catheterization, and haemodynamic variables and coronary flow velocity were measured. All of the patients also underwent treadmill exercise testing.

MAIN OUTCOME MEASURES

Left ventricular mass was evaluated by echocardiography. The coronary flow velocity data were obtained by using the intracoronary Doppler catheter technique. ST-segment depression was observed on the exercise electrocardiogram.

RESULTS

Systemic vascular resistance did not differ, whereas total arterial compliance was decreased in the ISH patients versus the controls (P < 0.001). The left ventricular mass of the ISH patients was increased slightly, but their left ventricular systolic wall stress was greater than that of the controls (P < 0.01). The coronary flow reserve ratio and the ratio of diastolic to total coronary flow were decreased in the ISH patients versus the controls (P < 0.01). ST-segment depression on the exercise electrocardiogram was frequently observed in the hypertensive patients (80 versus 0% in control subjects, P < 0.01).

CONCLUSIONS

Patients with ISH were characterized haemodynamically by a decrease in arterial compliance. They showed an increase in left ventricular systolic wall stress and also showed decreases in coronary flow reserve ratio and in the relative diastolic coronary flow. Such alterations observed in patients with ISH are detrimental to the heart and may contribute to a reduced exercise capacity and the induction of subendocardial ischaemia during exercise.

Effect of warming of exercising legs on exercise capacity in patients with impaired exercise tolerance

OBJECTIVE

The purpose of this study was to determine whether warming of exercising legs improves exercise capacity in patients with cardiac disease and low exercise tolerance.

BACKGROUND

Exercising muscle temperature reflects both muscle metabolic rate and muscle blood flow. Increase in muscle temperature in exercising legs is impaired in patients with chronic heart failure. We hypothesized that the mechanisms responsible for impairment of temperature increase in exercising muscle might be related to those responsible for low exercise tolerance.

METHODS

We studied 17 patients with cardiac disease whose anaerobic threshold (AT) ranged from 6.6 to 14.8 ml/kg/min (mean 11.2 +/- 1.9 SD). Subjects performed symptom-limited sitting cycle ergometer exercise with or without warming of the thighs. Both thighs were warmed by use of hot packs fixed by supporters. To determine the effect of the supporters themselves on AT and peak VO2, the same ergometer exercise was performed by 7 patients with or without supporters. Peak VO2 and AT were determined by concomitant respiratory gas monitoring.

RESULTS

1) Warming of the thighs increased deep temperature in the thighs (1.0 approximately 2.8 degrees C). 2) AT and peak VO2 were significantly improved in the warming exercise compared with the non-warming exercise (p < 0.01, p < 0.01). 3) There was no significant difference in AT or peak VO2 between the exercise with and without supporters.

CONCLUSION

The findings of this study indicate that warming of exercising legs improves exercise capacity in patients with cardiac disease and low exercise tolerance.

Pathophysiologic significance of left ventricular hypertrophy in dilated cardiomyopathy

BACKGROUND AND HYPOTHESIS

Patients with dilated cardiomyopathy (DCM) with left ventricular hypertrophy (LVH) have been found to have a better prognosis than patients without LVH. However, the pathophysiologic mechanism for that has not been investigated. We sought to clarify the pathophysiologic significance of LVH in DCM.

METHODS

We performed isoproterenol infusion echocardiography (0.02 micrograms/kg/min) in 17 patients with DCM, and measured plasma epinephrine and norepinephrine levels at rest and at the end of ergometer exercise in 14 of the 17 patients. Patients were classified into groups according to the presence (9 patients) (LVH+) or absence (8 patients) (LVH-) of LVH. Left ventricular hypertrophy was defined as an inter-ventricular thickness or posterior wall thickness > or = 13 mm.

RESULTS

Although there was no significant difference between groups in fractional shortening at rest during isoproterenol infusion, fractional shortening was significantly higher in the LVH(+) group than in the LVH(-) group (29 +/- 9 vs. 17 +/- 8%; p < 0.025). Although there was no significant difference in plasma norepinephrine level, it was significantly lower in the LVH(+) group than in the LVH(-) group (233 +/- 169 vs. 519 +/- 258 pg/ml; p < 0.05) at the end point of the exercise.

CONCLUSION

Systolic reserve, represented by the response to isoproterenol, is greater in patients with DCM with LVH than in those without LVH, and a lower plasma level of norepinephrine is needed to activate the myocardium during exercise in patients with DCM with LVH. This pathophysiologic characteristic could be one of the mechanisms which explain a better prognosis in patients with DCM with LVH.

[Class-I antiarrhythmic drugs]

Classification, mechanism of action, pharmacokinetic properties and clinical applications of class-I antiarrhythmic agents were summarized. Class-I drugs were subdivided into three groups, Ia, Ib, Ic. This subclassification is based on their action to modify the action potential duration. In the Cardiac Arrhythmia Suppression Trial (CAST), flecainide and encainide were associated with greater mortality than placebo in patients with non-life threatening arrhythmias. Results of CAST and other megatrials suggested that antiarrhythmic agents were unsafe in some groups of patients and the limitation of antiarrhythmic therapy. Proarrhythmia and combination therapy of antiarrhythmic agents were mentioned.

Effect of percutaneous transluminal coronary angioplasty on exercise ventilation in patients with coronary artery disease and normal left ventricular function

We evaluated the ventilatory response to exercise before and after percutaneous transluminal coronary angioplasty (PTCA) in 22 patients with coronary artery disease (CAD) and normal left ventricular systolic function to determine the effect of exercise-induced myocardial ischemia on the ventilatory response. Subjects performed a symptom-limited maximal ergometer exercise test in the sitting position. The ventilatory response was evaluated in terms of the slopes of minute ventilation (VE) and carbon dioxide production (VCO2) during exercise (slope 1 and slope 2, defined as below and above the respiratory compensation threshold, respectively). Slope 1 of the correlation between (VE) and (VCO2) was significantly greater in patients with CAD (27.3 +/- 2.6) than in the age-matched control group (23.7 +/- 2.6; p < 0.01). Slope 2 was also significantly greater in patients (41.0 +/- 4.8) than in the control group (29.7 +/- 2.9; p < 0.01). Slope 1 of the correlation between (VE) and (VCO2) decreased significantly in the 14 patients in whom PTCA was successful but did not decrease in the 8 patients in whom PTCA failed. Our results suggest that myocardial ischemia increases exercise ventilation in patients with CAD and normal left ventricular systolic function and that its effect is reversible.

Vasoconstriction by endothelin-1 in resistance and conduit portions of isolated human mesenteric arteries

Although physiological processes related to vascular function differ greatly between resistance arteries and conduit arteries, it is not known whether the effects of endothelin-1 on these arteries differ in humans. In the present study, the conduit portion and the resistance portion of isolated human mesenteric arteries were suspended in a Krebs-Ringer solution. Norepinephrine and endothelin-1 produced concentration-dependent contractions in both portions. The EC50 value of norepinephrine in the resistance portion (3.7 x 10(-7) M, n = 8) did not differ from that in the conduit portion (3.4 x 10(-7) M, n = 7). However, the EC50 value of endothelin-1 in the resistance portion (3.0 x 10(-9) M, n = 8) was significantly lower than that in the conduit portion (1.1 x 10(-8) M, n = 7, P < 0.05). Although the maximum response to norepinephrine in the resistance portion (calculated as the percentage of 50 mM KCl-induced contraction) did not differ from that in the conduit portion, the maximum response to endothelin-1 in the resistance portion was significantly greater than that in the conduit portion. These results indicate that endothelin-1 induces more potent constriction in resistance portion than in conduit portion in isolated human mesenteric arteries.

Endogenous endothelin-1 participates in the maintenance of cardiac function in rats with congestive heart failure. Marked increase in endothelin-1 production in the failing heart

BACKGROUND

Although it was demonstrated that circulating endothelin-1 (ET-1) levels are elevated in congestive heart failure (CHF), the production and roles of ET-1 in the failing heart are not known. We investigated the production of ET-1 in the heart and the density of myocardial ET receptors in rats with CHF. We also investigated the effects of intravenously infused BQ-123, an endothelin(A) (ETA) receptor antagonist, on both heart and myocardial contractility in rats with CHF.

METHODS AND RESULTS

We used the left coronary artery-ligated rat model of CHF (CHF rats). Three weeks after surgery, the rats developed CHF. Plasma ET-1 concentration was significantly higher in the CHF rats than in the sham-operated rats (P<.01). In the left ventricle, the expression prepro-ET-1 mRNA was markedly higher in the CHF rats than in the sham-operated rats. The peptide level of ET-1 in the left ventricle was also significantly higher in the CHF rats than in the sham-operated rats (500+/-41 versus 102+/-10 pg/g tissue, P<.01). Myocardial ET receptors were significantly higher in the CHF rats than in the sham-operated rats (243+/-20 versus 155+/-17 fmol/mg protein, P<.05). In the CHF rats, intravenous BQ-123 infusion (0.1 mg x kg(-1) x min(-1) for 120 minutes) significantly decreased both heart rate (P<.01) and LV+dP x dt(max) (P<.05) but not mean blood pressure. BQ-123 infusion did not affect these hemodynamic parameters in the sham-operated rats.

CONCLUSIONS

In the present study, we demonstrated that the production of ET-1 in the heart is markedly increased and that the density of myocardial ET receptors is significantly elevated in the CHF rats. Intravenous BQ-123 infusion significantly reduced both heart rate and LV+dP/dt(max) in the CHF rats but not in the sham-operated rats. Therefore, the ET receptor-mediated signal transduction system in the heart appears to be markedly stimulated in the CHF rats, and endogenous ET-1 may be involved in the maintenance of the cardiac function in these rats.