Yasuhide Nakashima

Asymmetric Dimethylarginine Produces Vascular Lesions in Endothelial Nitric Oxide Synthase–Deficient Mice: Involvement of Renin-Angiotensin System and Oxidative Stress

Objective—Asymmetric dimethylarginine (ADMA) is widely believed to be an endogenous nitric oxide synthase (eNOS) inhibitor. However, in this study, we examined our hypothesis that the long-term vascular effects of ADMA are not mediated by inhibition of endothelial NO synthesis. Methods and Results—ADMA was infused in wild-type and eNOS-knockout (KO) mice by osmotic minipump for 4 weeks. In wild-type mice, long-term treatment with ADMA caused significant coronary microvascular lesions. Importantly, in eNOS-KO mice, treatment with ADMA also caused an extent of coronary microvascular lesions that was comparable to that in wild-type mice. These vascular effects of ADMA were not prevented by supplementation of l-arginine, and vascular NO production was not reduced by ADMA treatment. Treatment with ADMA caused upregulation of angiotensin-converting enzyme (ACE) and an increase in superoxide production that were comparable in both strains and that were abolished by simultaneous treatment with temocapril (ACE inhibitor) or olmesartan (AT1 receptor antagonist), which simultaneously suppressed vascular lesion formation. Conclusions—These results provide the first direct evidence that the long-term vascular effects of ADMA are not solely mediated by simple inhibition of endothelial NO synthesis. Direct upregulation of ACE and increased oxidative stress through AT1 receptor appear to be involved in the long-term vascular effects of ADMA in vivo.

Asymmetric Dimethylarginine Causes Arteriosclerotic Lesions in Endothelial Nitric Oxide Synthase-Deficient Mice. Involvement of Renin-Angiotensin System and Oxidative Stress

Objective—Asymmetric dimethylarginine (ADMA) is widely believed to be an endogenous nitric oxide synthase (eNOS) inhibitor. However, in this study, we examined our hypothesis that the long-term vascular effects of ADMA are not mediated by inhibition of endothelial NO synthesis. Methods and Results—ADMA was infused in wild-type and eNOS-knockout (KO) mice by osmotic minipump for 4 weeks. In wild-type mice, long-term treatment with ADMA caused significant coronary microvascular lesions. Importantly, in eNOS-KO mice, treatment with ADMA also caused an extent of coronary microvascular lesions that was comparable to that in wild-type mice. These vascular effects of ADMA were not prevented by supplementation of l-arginine, and vascular NO production was not reduced by ADMA treatment. Treatment with ADMA caused upregulation of angiotensin-converting enzyme (ACE) and an increase in superoxide production that were comparable in both strains and that were abolished by simultaneous treatment with temocapril (ACE inhibitor) or olmesartan (AT1 receptor antagonist), which simultaneously suppressed vascular lesion formation. Conclusions—These results provide the first direct evidence that the long-term vascular effects of ADMA are not solely mediated by simple inhibition of endothelial NO synthesis. Direct upregulation of ACE and increased oxidative stress through AT1 receptor appear to be involved in the long-term vascular effects of ADMA in vivo.

Suppression of atherosclerosis in cholesterol-fed rabbits by diltiazem injection.

The effects of diltiazem, a calcium antagonist, on the development of atherosclerosis were studied in Japanese white rabbits. The rabbits were examined at the end of 10 weeks on the following regimens; 1) a diet of standard pellets and daily intraperitoneal (ip) injections of saline; 2) a diet of pellets containing 1% cholesterol and daily ip injections of saline; or 3) a diet of pellets containing 1% cholesterol and daily ip injections of diltiazem (50 mg). The plasma total and LDL cholesterol levels for the third group were significantly lower than those of the cholesterol diet group. Macroscopically, atheromatous lesions covered 26.7% ± 6.7% (mean ± SE) of the intimal surface of the aorta in the second group, and 0.7% ± 0.3% in the third group (p < 0.005). The levels of cholesterol, calcium, and uronic acid in the aortic tissue of the second group were significantly higher than those in the third. We concluded that diltiazem administered intraperitoneally suppresses the plasma total and LDL cholesterol elevation induced by the cholesterol diet and inhibits experimentally-induced atherosclerosis.

The Incidence and Risk Factors for Venous Obstruction After Implantation of Transvenous Pacing Leads

OGINOSAWA, Y., et al.: The Incidence and Risk Factors For Venous Obstruction After Implantation of Transvenous Pacing Leads. Several investigators have shown that the incidence of venous obstruction after pacemaker implantation was observed in 31–50% of pacemaker patients. However, these previous reports did not investigate the venous system prior to implantation. The aim of this study was to determine the incidence and risk factors for venous obstruction in patients with transvenous pacing leads. The study included 131 consecutive patients (64 men, 67 women; mean age 71.3 ± 9.8 years) who were investigated using intravenous digital subtraction angiography (DSA) before and after permanent pacemaker implantation. Follow‐up DSA was performed for a mean interval of 44 ± 6 months after pacemaker lead implantation in 79 of 131 patients. A diameter narrowing > 60% was defined as an obstruction. Prior to implantation of pacing leads, venous obstruction was present in 18 (13.7%) of 131 patients. In 15 of these 18 patients, the obstruction was present at the site of the left innominate vein. Follow‐up DSA, after implantation of pacing leads, showed that venous obstruction was observed in 26 (32.9%) of 79 patients. There were no significant differences between obstruction and nonobstruction groups in terms of age, sex, cardiothoracic ratio, left atrial dimension, left ventricular ejection fraction, baseline heart diseases for indication of pacemaker implantation, or number and body size of pacing leads. Neither clinical symptoms nor abnormal physical findings were observed in any patients. In conclusion, the incidence of venous obstruction after pacing lead implantation is less than that of previous reports, which might be related to the incidence of venous obstruction before pacing leads implantation.

Vasculoprotective roles of neuronal nitric oxide synthase

Nitric oxide (NO) has multiple important actions that contribute to the maintenance of vascular homeostasis. NO is synthesized by three different isoforms of NO synthase (NOS), all of which have been reported to be expressed in human atherosclerotic vascular lesions. Although the regulatory roles of endothelial NOS (eNOS) and inducible NOS (iNOS) on the development of atherosclerosis have been described, little is known about the role of neuronal NOS (nNOS). Here, we show that nNOS also exerts important vasculoprotective effects in vivo. In a carotid artery ligation model, nNOS gene‐deficient (nNOS‐KO) mice exhibited accelerated neointimal formation and constrictive vascular remodeling caused by blood flow disruption. In a rat balloon injury model, the selective inhibition of nNOS activity potently enhanced vasoconstrictor responses to a variety of calcium‐mobilizing stimuli, suppressed tissue cGMP concentrations, a marker of vascular NO production, and exacerbated neointimal formation. In both models, nNOS was absent before injury and was up‐regulated only after the injury, and was predominantly expressed in the neointima and medial smooth muscle cells. These results provide the first direct evidence that nNOS plays important roles in suppressing arteriosclerotic vascular lesion formation in vivo.

Comparison of Dobutamine Stress Echocardiography and Stress Thallium-201 Single-Photon Emission Computed Tomography for Detecting Coronary Artery Disease

Dobutamine stress echocardiography and stress thallium-201 single-photon emission computed tomography (SPECT) were compared for detecting coronary artery disease in 120 consecutive patients who underwent concomitant quantitative coronary angiography. The left ventricle was divided into anterior, inferior, and lateral regions. Wall motion or perfusion abnormalities observed within each region were classified as ischemia or fixed abnormality. Both tests showed 81% agreement in all 120 patients. Complete agreement was observed in 77% of the 360 regions analyzed. The overall sensitivity of dobutamine stress echocardiography and thallium-201 SPECT for the detection of coronary artery disease was 85% and 89%, and the specificity was 93% and 85%, respectively. A good correlation was found between the wall motion score index and perfusion defect size at peak stress and at rest (r = 0.70). Dobutamine stress echocardiography and thallium-201 SPECT exhibit a comparable accuracy for diagnosing coronary artery disease, localizing coronary artery stenosis, and detecting regional myocardial abnormalities. The wall motion score index may be useful for evaluating the myocardial area at risk.

Statin Treatment Upregulates Vascular Neuronal Nitric Oxide Synthase Through Akt/NF-κB Pathway

Objective—Three-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) are known to enhance vascular expression of endothelial (eNOS) and inducible nitric oxide synthase (iNOS). In this study, we examined whether statins also upregulate vascular expression of neuronal NOS (nNOS). Methods and Results—In cultured rat aortic smooth muscle cells, treatment with atorvastatin significantly increased nNOS expression, associated with activation of Akt and NF-&kgr;B. Inhibition of Akt by dominant-negative Akt suppressed atorvastatin-induced nNOS expression as well as Akt and NF-&kgr;B activation. Inhibition of NF-&kgr;B by dominant-negative I&kgr;B also attenuated atorvastatin-induced nNOS expression and NF-&kgr;B activation, but not Akt activation. We further examined whether atorvastatin also enhances nNOS expression in isolated mouse aorta, and if so, how much nNOS-derived NO accounts for atorvastatin-induced NOx production. In isolated aortas of wild-type mice, atorvastatin significantly increased all three NOS isoform expression and NOx production. In isolated aortas of doubly i/eNOS−/−, n/eNOS−/−, and n/iNOS−/− mice, which express only nNOS, iNOS, and eNOS, respectively, atorvastatin-induced NOx production was approximately 25%, 25%, and 50% to that of wild-type mice, respectively, suggesting that nNOS accounts for 25% of the atorvastatin-mediated NOx production. Conclusions—These results indicate that atorvastatin upregulates vascular nNOS through Akt/NF-&kgr;B pathway, demonstrating a novel nNOS-mediated vascular effect of the statin.

Rate-dependent QT shortening mechanism for the LQT3 ΔKPQ mutant

Objective: For the congenital long QT (LQT) syndrome involving mutations of the cardiac sodium channel gene SCN5A , LQT3, the initiation of sudden cardiac death tends to be bradycardia- or pause-dependent, contrary to other LQT syndromes that tend to be adrenergic dependent. Enhanced shortening of the prolonged QT interval with increased heart rate has been reported in LQT3 patients. We hypothesized that the rate-dependent shortening of the QT interval may be attributed to the kinetic properties of inactivation the late sodium current ( I Na) in LQT3. Methods: The ΔKPQ mutant of the human heart voltage-gated sodium channel α-subunit was stably transfected into a mammalian cell line (HEK293). I Na was recorded using a whole-cell patch-clamp technique. Results: A train of 50 depolarizing pulses or a train of 50 ventricular action potential waveforms was applied with different interpulse durations. Peak I Na for the 50th pulse compared with that of I Na in the first pulse was decreased <2% for interpulse durations as short as 20 ms, but late I Na amplitude measured at the end of the pulse was decreased 95, 78, 68, 56 and 47% with 1000, 500, 200, 100, 20 ms interpulse intervals, respectively. Using the action potential waveform a similar rate-dependent reduction of late I Na was found with minimal reduction of peak I Na. Conclusions: Late I Na amplitude in the ΔKPQ mutation is strongly rate dependent. Rate-dependent reductions of late I Na may cause shortening the QT interval at higher rates. This provides a mechanism correlating the genotype with the clinical phenotype, and provides a rationale for the effectiveness of pacemaker therapy in LQT3 patients.

Usefulness of orthostatic self-training for the prevention of neurocardiogenic syncope.

ABE H., et al.: Usefulness of Orthostatic Self‐Training for the Prevention of Neurocardiogenic Syncope. To clarify the effectiveness of an orthostatic self‐training program for the prevention of neurocardiogenic syncope, twenty‐four consecutive head‐up tilt induced syncopal patients (12 men, 12 women; mean age 34 ± 20 years) were treated with an orthostatic self‐training program. The syncope was induced by head‐up tilt testing (+ 80 degrees for 30 minutes) with or without the use of isoproterenol in all patients reproducibly. The hemodynamics during the syncope were of the cardioinhibitory type in 4, vasodepressor type in 7, and mixed type in 13 patients. The onset time of the tilt induced syncope was 16 ± 10 minutes after the upright position. The orthostatic self‐training included standing against a wall without moving twice a day every day for a planned duration of up to 30 minutes at home. The head‐up tilt response was reevaluated with the same protocol as the initial study after 22 ± 6 days based on the patients daily recording of the self‐training, and the clinical effect of the training program performed only once a day at home was noted over a mean follow‐up of 9.5 ± 3.4 months (range 5–18 months). Tilt induced syncope after the self‐training was observed in 2 of 24 patients. However, spontaneous syncope was not observed in any of the patients during follow‐up. In conclusion, orthostatic self‐training significantly improved the symptoms in patients with neurocardiogenic syncope. Once a day training for up to 30 minutes was effective and easily accepted by the patients for the prevention of neurocardiogenic syncope.

Autonomic cardiovascular responses to hypercapnia in conscious rats: the roles of the chemo- and baroreceptors

The role of the autonomic nervous system, the central and peripheral chemoreceptors, and the arterial baroreceptors was examined in the cardiovascular response to hypercapnia in conscious rats chronically instrumented for the measurement of arterial blood pressure (ABP), heart rate (HR), and renal sympathetic nerve activity (RSNA). Rats were exposed to hypercapnia (6% CO2), and the cardiovascular and autonomic nervous responses in intact and carotid chemo- and/or aortic denervated rats were compared. In intact and carotid chemo-denervated rats, hypercapnia induced significant increases in mean ABP (MABP) and RSNA, and a significant decrease in HR. The HR decrease was reversed by atropine and eliminated by bilateral aortic denervation, which procedure, however, did not affect the MABP or RSNA response. Bilateral carotid chemo-denervation did not affect the baroreflex control of HR, although this control was attenuated by aortic denervation. Hypercapnia did not affect baroreflex sensitivity in intact rats. These results suggest that hypercapnia induces an increase in MABP due to an activation of sympathetic nervous system via central chemoreceptors and a decrease in HR due to a secondary reflex activation of the parasympathetic nervous system via arterial baroreceptors in response to the rise in ABP. In addition, carotid chemoreceptors do not play a major role in the overall cardiovascular response to hypercapnia in conscious rats. The mechanism responsible for the parasympatho-excitation may also involve CO2 induced aortic chemoreceptor simulation.