Role of inducible nitric oxide synthase in rostral ventrolateral medulla in blood pressure regulation in spontaneously hypertensive rats.

Nitric oxide (NO) in the brainstem modulates blood pressure (BP). Overexpression of inducible NO synthase (iNOS) in the rostral ventrolateral medulla (RVLM) increases BP in normotensive Wistar-Kyoto rats (WKY), but its role in BP regulation in spontaneously hypertensive rats (SHR) is unknown. We examined iNOS expression and the effect of iNOS inhibitors in the RVLM on BP and heart rate in SHR and WKY. iNOS levels in the RVLM were significantly higher in SHR than in WKY. Bilateral microinjection of aminoguanidine into the RVLM dose-dependently decreased BP and heart rate in SHR, but not in WKY. These findings suggest that iNOS expression in the RVLM of SHR contributes to increase BP.

Activation of Rho-kinase in the brainstem enhances sympathetic drive in mice with heart failure.

Rho-kinase is involved in the pathogenesis of hypertension and left ventricular remodelling after myocardial infarction (MI). In an earlier study, we had demonstrated that Rho-kinase in the brainstem contributes to hypertensive mechanisms via the sympathetic nervous system; however, it is not known whether Rho-kinase in the brainstem also contributes to sympathetic nerve activation after MI. Male Institute of Cancer Research mice (8-10 weeks old) were used for the study. Two days before coronary artery occlusion (MI group), the left ventricular function was estimated by echocardiography. Following this, Y-27632 (0.5 mM, 0.25 microL/h), a specific Rho-kinase inhibitor, or a vehicle was intracisternally infused in the mice using an osmotic mini-pump. Nine days after coronary artery occlusion, we evaluated the 24-hour urinary norepinephrine excretion (U-NE) as a marker of sympathetic nerve activity. Ten days after coronary artery occlusion, we measured organ weight and evaluated Rho-kinase activity in the brainstem by measuring the amount of phosphorylated ezrin/radixin/moesin proteins, one of the substrates of Rho-kinase. The control group underwent a sham operation. Rho-kinase activity, U-NE, and lungs and liver weight were significantly greater in the MI group compared with the control group. Left ventricular size increased and percent fractional shortening decreased in the MI group compared with the control group. Y-27632 significantly decreased Rho-kinase activity and attenuated the increase in U-NE after MI. These results demonstrate that Rho-kinase is activated in the brainstem after MI and that the activation of this pathway is involved in the resulting enhanced sympathetic drive.

Effects of valsartan or amlodipine on endothelial function and oxidative stress after one year follow-up in patients with essential hypertension.

Endothelial function is impaired in hypertensive patients. Decreased nitric oxide production and increased oxidative stress are involved in this abnormality. The aim of the present study was to evaluate whether endothelial function and oxidative stress differ following long-term antihypertensive treatment with an angiotensin type 1 receptor blocker, valsartan, or a calcium channel blocker, amlodipine, in patients with essential hypertension. Hypertensive patients were treated with valsartan (80-160 mg/day) or amlodipine (5-10 mg/day) for one year (n = 9 for each). The baseline blood pressure was similar between groups, and the magnitude of the decreases in blood pressure did not differ during treatment at three months, six months, or one year. Endothelial function and oxidative stress markers were examined before and after treatment. Endothelial function, assessed by flow-mediated vasodilation, was significantly improved in hypertensive patients treated with valsartan (5.8 +/- 1.2 to 10.7 +/- 1.4 %, p < 0.01) but not in those treated with amlodipine. The percent increase in vasodilation induced by sublingual nitroglycerin did not differ between the two groups. As markers of oxidative stress, urinary excretion of 8-isoprostane and 8-hydroxy-2'-deoxyguanosine was significantly reduced in patients treated with valsartan, but not in those treated with amlodipine. These findings suggest that the treatment of hypertensive patients with valsartan for at least one year improves endothelial function in association with reduced oxidative stress. The improved endothelial function and reduced oxidative stress might be involved in the benefits of anti-hypertensive treatment beyond simply lowering blood pressure, although the effects of treatment with valsartan or amlodipine over a much longer period are unknown.

Three fatal cases of rapidly progressive infective endocarditis caused by Staphylococcus aureus: one case with huge vegetation.

Staphylococcus aureus (S. aureus) infective endocarditis (IE) is a severe disease with a high mortality despite intensive therapy. Three cases of S. aureus IE had a rapidly progressive fatal clinical course despite intensive antimicrobial therapy. One case was methicillin-sensitive S. aureus IE, which formed rapidly growing a huge vegetation on a prosthetic mitral valve, complicated with multiple systemic emboli. The other 2 cases were methicillin-resistant S. aureus IE without any predisposing heart disease.

Pressor response induced by central angiotensin II is mediated by activation of Rho/Rho-kinase pathway via AT1 receptors.

OBJECTIVES: The brain renin-angiotensin system plays an important role in cardiovascular regulation and the pathogenesis of hypertension. Angiotensin II activates the Rho/Rho-kinase pathway in vascular smooth muscle cells and cardiomyocytes in vitro. The aim of the present study was to determine whether angiotensin II in the brainstem activates the Rho/Rho-kinase pathway, and, if so, whether this mechanism is involved in the central pressor action of angiotensin II. METHODS AND RESULTS: Angiotensin II infused intracisternally for 7 days in Wistar-Kyoto rats (WKY) increased systolic blood pressure (SBP) and urinary norepinephrine excretion. These responses were abolished by the co-infusion of Y-27632, a specific Rho-kinase inhibitor, or valsartan. The intracisternal infusion of Y-27632 or valsartan also reduced SBP and norepinephrine excretion in spontaneously hypertensive rats (SHR). Western blot analysis was performed to examine the expression levels of membranous RhoA and phosphorylated ezrin, radixin, and moesin (p-ERM), which reflects Rho/Rho-kinase activity. The expression levels of membranous RhoA and p-ERM in the brainstem were significantly greater in both angiotensin II-treated WKY and SHR than in vehicle-treated WKY. Valsartan reduced the expression levels of membranous RhoA and p-ERM in angiotensin II-treated WKY and SHR. Y-27632 reduced the expression levels of p-ERM in angiotensin II-treated WKY and SHR. CONCLUSIONS: These results suggest that the pressor response induced by intracisternally infused angiotensin II is substantially mediated by the activation of the Rho/Rho-kinase pathway via AT1 receptors of the brainstem in WKY, and that this pathway might be involved in the hypertensive mechanisms of SHR.

Long-acting calcium channel blocker, azelnidipine, increases endothelial nitric oxide synthase in the brain and inhibits sympathetic nerve activity.

Nitric oxide (NO) in the central nervous system inhibits sympathetic nerve activity, thereby decreasing blood pressure. It is unknown, however, whether orally administered antihypertensive treatment alters NO synthase (NOS) expression, particularly in the brain, and how changes in NOS expression affects sympathetic nerve activity. Azelnidipine, a recently developed long-acting dihydropyridine calcium channel blocker, does not cause baroreflex-induced tachycardia. The aim of the present study was to determine whether antihypertensive treatment with azelnidipine alters endothelial NOS (eNOS), neuronal NOS (nNOS), or inducible NOS (iNOS) expression in the brain, and how changes in NOS affect sympathetic nerve activity. Azelnidipine (20 mg/kg/day) or hydralazine (20 mg/kg/day) was orally administered for 30 days in stroke-prone spontaneously hypertensive rats (SHRSP). Blood pressure and heart rate were measured by the tail cuff method. Urinary norepinephrine excretion was measured as a marker of sympathetic nerve activity. Western blot analysis was performed to examine eNOS, nNOS, or iNOS expression levels in the brain (cortex, cerebellum, hypothalamus, and the brain stem), heart, and aorta. The extent of blood pressure reduction was similar between the two groups. Heart rate increased in the hydralazine-treated group but did not change in the azelnidipine-treated group. Urinary norepinephrine excretion was significantly increased only in the hydralazine-treated group. Treatment with azelnidipine significantly increased eNOS expression levels in the brain, heart, and aorta, but did not alter nNOS or iNOS expression levels. Treatment with hydralazine did not change any of the NOS expression levels. These results suggest that antihypertensive treatment with azelnidipine attenuates reflex-induced sympathetic activation and enhances eNOS expression levels in the brain as well as in the heart and aorta.

Ovariectomy augments hypertension through rho-kinase activation in the brain stem in female spontaneously hypertensive rats.

Estrogen protects against increases in arterial pressure (AP) by acting on blood vessels and on cardiovascular centers in the brain. The mechanisms underlying the effects of estrogen in the brain stem, however, are not clear. The aim of the present study was to determine whether ovariectomy affects AP via the Rho/Rho-kinase pathway in the brain stem. We performed bilateral ovariectomy in 12-week-old female spontaneously hypertensive rats. AP and heart rate (HR), measured using radiotelemetry in awake rats, were increased in ovariectomized rats compared with control rats (mean AP: 163+/-3 versus 144+/-4 mm Hg; HR: 455+/-4 versus 380+/-6 bpm). Continuous intracisternal infusion of Y-27632 significantly attenuated the ovariectomy-induced increase in AP and HR (mean AP: 137+/-6 versus 163+/-3 mm Hg; HR: 379+/-10 versus 455+/-4 bpm). In addition, we confirmed the increase of Rho-kinase activity in the brain stem in ovariectomized rats, and the increase was attenuated by intracisternal infusion of Y-27632 via the phosphorylated ezrin, radixin, and moesin (ERM) family, which are Rho-kinase target proteins. Furthermore, angiotensin II type 1 receptor expression in the brain stem was significantly greater in ovariectomized rats than in control rats, and the increase was partially reduced by intracisternal infusion of Y-27632. In a separate group of animals, we confirmed that the serum and cerebrospinal fluid 17beta-estradiol concentrations decreased in ovariectomized rats. These results suggest that depletion of endogenous estrogen by ovariectomy, at least in part, induces hypertension in female spontaneously hypertensive rats via activation of the renin-angiotensin system and the Rho/Rho-kinase pathway in the brain stem.

Amlodipine-induced reduction of oxidative stress in the brain is associated with sympatho-inhibitory effects in stroke-prone spontaneously hypertensive rats.

Amlodipine is a dihydropyridine calcium channel blocker that is widely used for the treatment of hypertensive patients and has an antioxidant effect on vessels in vitro. The aim of the present study was to examine whether treatment with amlodipine reduced oxidative stress in the brains of stroke-prone spontaneously hypertensive rats (SHRSP). The animals received amlodipine, nicardipine or hydralazine for 30 days in their drinking water. Levels of thiobarbituric acid-reactive substances (TBARS) in the brain (cortex, cerebellum, hypothalamus, and brainstem) were measured before and after each treatment. Systolic blood pressure decreased to similar levels in the amlodipine-, nicardipine-, and hydralazine-treated groups. Urinary norepinephrine excretion was significantly reduced in SHRSP after treatment with amlodipine, but not with nicardipine or hydralazine. Levels of TBARS in the cortex, cerebellum, hypothalamus, and brainstem were significantly higher in SHRSP than in Wistar-Kyoto rats (WKY), and were reduced in amlodipine-treated, but not in nicardipine- or hydralazine-treated, SHRSP. Electron spin resonance spectroscopy revealed increased levels of reactive oxygen species in the brains of SHRSP, which were reduced by treatment with amlodipine. Intracisternal infusion of amlodipine also reduced systolic blood pressure, urinary norepinephrine excretion, and the levels of TBARS in the brain. These results suggested that oxidative stress in the brain was enhanced in SHRSP compared with WKY rats. In addition, antihypertensive treatment with amlodipine reduced oxidative stress in all areas of the brain examined and decreased blood pressure without a reflex increase in sympathetic nerve activity in SHRSP.

Inhibition of rho-kinase in the nucleus tractus solitarius enhances glutamate sensitivity in rats.

The Rho/Rho-kinase pathway in the central nervous system is involved in the maintenance of dendritic spines, which form the postsynaptic contact sites of excitatory synapses. Inhibition of the Rho-kinase pathway in neuron promotes dendritic spines or branches. In contrast, activation of the Rho/Rho-kinase pathway reduces dendritic spines or branches. Recent studies suggest that morphological changes of dendritic spines occur rapidly, and spine morphology is associated with glutamate sensitivity. The aim of the present study was to determine whether Rho-kinase activity affects glutamate sensitivity in the nucleus tractus solitarii (NTS) of Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). We first examined the effects of unilateral glutamate injection in the NTS. There was a significantly smaller decrease in arterial pressure in SHR than in WKY. We then examined the depressor responses evoked by unilateral glutamate injection into the NTS after preinjection of Y-27632, a specific Rho-kinase inhibitor. Preinjection of Y-27632 enhanced the glutamate response in both strains. However, the magnitude of the augmentation was significantly greater in SHR than in WKY. Furthermore, we recorded single-unit activity of NTS neurons from medulla brain slice preparations. N-methyl-D-aspartate (NMDA) or alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) was applied iontophoretically to the recorded neurons, and neuronal activity was recorded before and after Y-27632 perfusion. Y-27632 perfusion increased the response to NMDA and AMPA. These results suggest that inhibition of Rho-kinase activity in the NTS enhances glutamate sensitivity in WKY and SHR and might improve impaired glutamate sensitivity in SHR.

Rho-kinase inhibitor improves increased vascular resistance and impaired vasodilation of the forearm in patients with heart failure.

BACKGROUND: Rho-kinase is suggested to have an important role in enhanced vasoconstriction in animal models of heart failure (HF). Patients with HF are characterized by increased vasoconstriction and reduced vasodilator responses to reactive hyperemia and exercise. The aim of the present study was to examine whether Rho-kinase is involved in the peripheral circulation abnormalities of HF in humans with the Rho-kinase inhibitor fasudil. METHODS AND RESULTS: Studies were performed in patients with HF (HF group, n=26) and an age-matched control group (n=26). Forearm blood flow was measured with a strain-gauge plethysmograph during intra-arterial infusion of graded doses of fasudil or sodium nitroprusside. Resting forearm vascular resistance (FVR) was significantly higher in the HF group than in the control group. The increase in forearm blood flow evoked by fasudil was significantly greater in the HF group than in the control group. The increased FVR was decreased by fasudil in the HF group toward the level of the control group. By contrast, FVR evoked by sodium nitroprusside was comparable between the 2 groups. Fasudil significantly augmented the impaired ischemic vasodilation during reactive hyperemia after arterial occlusion of the forearm in the HF group but not in the control group. Fasudil did not augment the increased FVR evoked by phenylephrine in the control group significantly. CONCLUSIONS: These results indicate that Rho-kinase is involved in increased FVR and impaired vasodilation of the forearm in patients with HF.

Effects of hydroxyfasudil administered to the nucleus tractus solitarii on blood pressure and heart rate in spontaneously hypertensive rats.

Previously, we reported that the inhibition of Rho-kinase by a microinjection of Y-27632 or the transfection of dominant-negative Rho-kinase into cells of the nucleus tractus solitarii (NTS) reduces blood pressure, heart rate, and sympathetic nerve activity. In the present study, we examined the effects of another Rho-kinase inhibitor, hydroxyfasudil, on blood pressure and heart rate in anesthetized rats. The results were compared between normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). The microinjection of hydroxyfasudil was performed unilaterally or bilaterally into the NTS of WKY rats and SHR. A unilateral microinjection of hydroxyfasudil elicited depressor and bradycardic responses in SHR but not in WKY rats. A bilateral microinjection of hydroxyfasudil elicited depressor and bradycardic responses in both SHR and WKY rats. However, the magnitude of the decrease in these variables was greater in SHR than in WKY rats. The expression levels of RhoA in the membrane fraction and phosphorylated ERM family (ezrin, radixin, and moesin) in the NTS were greater in SHR than in WKY rats. These results suggest that the microinjection of hydroxyfasudil into the NTS causes cardiovascular responses similar to those caused by Y-27632 and that these responses are probably mediated by the inhibition of Rho-kinase.

Overexpression of inducible nitric oxide synthase in rostral ventrolateral medulla causes hypertension and sympathoexcitation via an increase in oxidative stress.

The present study examined the role of inducible nitric oxide synthase (iNOS) in the rostral ventrolateral medulla (RVLM) of the brain stem, where the vasomotor center is located, in the control of blood pressure and sympathetic nerve activity. Adenovirus vectors encoding iNOS (AdiNOS) or beta-galactosidase (Adbetagal) were transfected into the RVLM in Wistar-Kyoto (WKY) rats. Blood pressure and heart rate were monitored using a radiotelemetry system. iNOS expression in the RVLM was confirmed by immunohistochemical staining or Western blot analysis. Mean arterial pressure significantly increased from day 6 to day 11 after AdiNOS transfection, but did not change after Adbetagal transfection. Urinary norepinephrine excretion was significantly higher in AdiNOS-transfected rats than in Adbetagal-transfected rats. Microinjection of aminoguanidine or S-methylisothiourea, iNOS inhibitors, or tempol, an antioxidant, significantly attenuated the pressor response evoked by iNOS gene transfer. The levels of thiobarbituric acid-reactive substances, a marker of oxidative stress, were significantly greater in AdiNOS-transfected rats than in Adbetagal-transfected rats. Dihydroethidium fluorescence in the RVLM was increased in AdiNOS-transfected rats. In addition, nitrotyrosine-positive cells were observed in the RVLM only in AdiNOS-transfected rats. Intracisternal infusion of tempol significantly attenuated the pressor response and the increase in the levels of thiobarbituric acid-reactive substances induced by AdiNOS transfection. These results suggest that overexpression of iNOS in the RVLM increases blood pressure via activation of the sympathetic nervous system, which is mediated by an increase in oxidative stress.

Inhibition of Rho-kinase in the brainstem augments baroreflex control of heart rate in rats.

The Rho/Rho-kinase pathway in the nucleus tractus solitarii (NTS) of the brain stem contributes to blood pressure regulation. Activation of this pathway might be involved in the central nervous system mechanisms of hypertension. The aim of the present study was to determine whether baroreflex control of heart rate is altered by inhibition of Rho-kinase in the NTS. Adenovirus vectors encoding dominant-negative Rho-kinase or beta-galactosidase were transfected into the nucleus tractus solitarii of Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). Baroreflex control of heart rate was examined by changing arterial pressure with an intravenous infusion of phenylephrine or sodium nitroprusside. The maximum gain of baroreflex control of heart rate was attenuated in SHR compared with WKY before the gene transfer. Transfection of adenovirus vectors encoding dominant-negative Rho-kinase significantly augmented the maximum gain in both WKY and SHR. The extent of this augmentation, however, was greater in SHR than in WKY. After treatment with metoprolol, the maximum gain was significantly decreased in rats transfected with adenovirus vectors encoding dominant-negative Rho-kinase, but not in nontransfected rats. In contrast, after treatment with atropine, the maximum gain was greater in rats transfected with adenovirus vectors encoding dominant-negative Rho-kinase compared with nontransfected rats, although it was decreased in both groups. These results suggest that inhibition of Rho-kinase in the NTS augments baroreflex control of heart rate, in both WKY and SHR, probably because of a cardiac sympathoinhibitory effect.

Long-term treatment with probucol improves endothelial function in patients with coronary artery disease.

Recent studies have shown that endothelial function is impaired in patients with coronary artery disease (CAD). Probucol has been recognized to have antioxidant properties as well as lipid-lowering effects, and may improve endothelial function. The aim of this study was to evaluate the effects of probucol on endothelial function in patients with CAD. We evaluated endothelial function, based on flow-mediated vasodilation during reactive hyperemia (FMD), and the intima-media thickness (IMT) of the common carotid artery using high resolution ultrasonography in patients either with (CAD group, n=26) or without CAD (Control group, n=12). We measured the serum cholesterol concentration, including the low-density lipoprotein cholesterol (LDL-cholesterol) concentration, and the plasma concentrations of homocyst(e)ine and asymmetric dimethylarginine (ADMA). Measurements of FMD and serum cholesterol were repeated after 3 months of probucol (500 mg/day, n=9) or placebo (n=9) treatment in patients with CAD. The IMT was significantly greater (p < 0.001) and FMD was significantly lower (p < 0.001) in the CAD group than in the Control group. While the serum cholesterol concentration and plasma ADMA were similar in the two groups, the plasma homocyst(e)ine concentrations were higher in the CAD group than in the Control group (p < 0.01). After probucol therapy, FMD was significantly improved in the CAD group (p < 0.05). The serum LDL-cholesterol concentration did not significantly decrease after probucol treatment. Placebo treatment did not alter FMD or the serum cholesterol concentration. Our findings suggest that long-term treatment with probucol improves endothelial function in patients with CAD, an outcome independent of the LDL-cholesterol-lowering effects of probucol, and that homocyst(e)ine may be a better predictor of atherosclerosis than ADMA.

Increased reactive oxygen species in rostral ventrolateral medulla contribute to neural mechanisms of hypertension in stroke-prone spontaneously hypertensive rats.

BACKGROUND: Oxidative stress increases in hypertension. The aim of this study was to determine whether reactive oxygen species (ROS) are increased in the rostral ventrolateral medulla (RVLM) in the brainstem, where the vasomotor center is located, in stroke-prone spontaneously hypertensive rats (SHRSP), and, if so, to determine whether the increased ROS contribute to neural mechanisms of hypertension in SHRSP. METHODS AND RESULTS: We measured ROS levels in the RVLM of SHRSP and compared them with those in Wistar-Kyoto rats (WKY). Thiobarbituric acid-reactive substances were increased in SHRSP compared with WKY. ROS were measured by electron spin resonance (ESR) spectroscopy. The ESR signal decay rate in the RVLM of SHRSP was significantly increased compared with that in WKY, and this increase was abolished by dimethylthiourea (a hydroxyl radical scavenger). The increased ESR signal decay rate was reduced to the same extent in the presence of desferrioxamine, catalase, and Tiron, indicating that hydroxyl radicals are derived from superoxide anions and hydrogen peroxide. In addition, total superoxide dismutase (SOD) activity in the RVLM was decreased in SHRSP compared with WKY. Furthermore, bilateral microinjection of tempol into the RVLM decreased blood pressure in SHRSP but not in WKY, and MnSOD overexpression in the RVLM of SHRSP decreased blood pressure and inhibited sympathetic nerve activity. CONCLUSIONS: These results suggest that superoxide anions in the RVLM, which generate hydroxyl radicals, are increased in SHRSP and contribute to the neural mechanisms of hypertension in SHRSP.

Rho/Rho-kinase pathway in the brainstem contributes to hypertension caused by chronic nitric oxide synthase inhibition.

Central nervous system mechanisms are involved in hypertension caused by chronic inhibition of nitric oxide (NO) synthesis. Chronic inhibition of NO synthesis might also activate the Rho/Rho-kinase pathway in the vasculature. We recently demonstrated that activation of the Rho/Rho-kinase pathway in the nucleus tractus solitarii (NTS) contributes to hypertensive mechanisms in spontaneously hypertensive rats. The aim of the present study was to determine whether activation of this pathway also contributes to neurogenic hypertensive mechanisms caused by chronic NO synthesis inhibition. The NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) was administered to Wistar-Kyoto rats in their drinking water (1 mg/mL) for 2 weeks. Bilateral microinjection of Y-27632, a specific Rho-kinase inhibitor, into the NTS elicited decreases in arterial pressure, heart rate, and renal sympathetic nerve activity in control rats and L-NAME-treated rats. The magnitude of the decrease, however, was significantly greater in L-NAME-treated than in control rats. In another group of rats, the specific Rho-kinase inhibitor, Y-27632, was administered intracisternally for 2 weeks with a mini-osmotic pump from the beginning of treatment with L-NAME. Y-27632 co-treatment significantly attenuated the increase in arterial pressure. Furthermore, the expression level of membranous RhoA and phosphorylation of the target proteins of Rho-kinase, the ERM (ezrin, radixin, moesin) family members, was significantly greater in L-NAME-treated rats than in control rats. These results indicate that activation of the Rho/Rho-kinase pathway in the NTS contributes to neurogenic hypertension caused by chronic NO synthase inhibition.

Role of endothelium-derived hyperpolarizing factor in human forearm circulation.

Endothelium-derived hyperpolarizing factor (EDHF) contributes to endothelium-dependent relaxation of isolated arteries, but it is not known whether this also occurs in the case of humans in vivo. The present study examined the role of EDHF in human forearm circulation. Forearm blood flow (FBF) was measured by strain-gauge plethysmography in 31 healthy, normal subjects (mean+/-SE age, 23+/-2 years; 24 men and 7 women). After oral administration of aspirin (486 mg), we infused NG-monomethyl-L-arginine (8 micromol/min for 5 minutes) into the brachial artery. We used tetraethylammonium chloride (TEA, 1 mg/min for 20 minutes), a KCa channel blocker, as an EDHF inhibitor, and nicorandil as a direct K+ channel opener. TEA significantly reduced FBF (P<0.05) but did not change systemic arterial blood pressure. Furthermore, TEA significantly inhibited the FBF increase in response to substance P (0.8, 1.6, 3.2, and 6.4 ng/min, n=8) and bradykinin (12.5, 25, 50, and 100 ng/min, n=8; both P<0.001), whereas it did not affect the FBF increase in response to acetylcholine (4, 8, 16, and 32 microg/min, n=8), sodium nitroprusside (0.4, 0.8, 1.6, and 3.2 microg/min, n=8), or nicorandil (0.128, 0.256, 0.512, and 1.024 mg/min, n=8). These results suggest that EDHF contributes substantially to basal forearm vascular resistance, as well as to forearm vasodilatation evoked by substance P and bradykinin in humans in vivo.

Overexpression of eNOS in RVLM improves impaired baroreflex control of heart rate in SHRSP. Rostral ventrolateral medulla. Stroke-prone spontaneously hypertensive rats.

We previously demonstrated that the overexpression of endothelial nitric oxide synthase (eNOS) in the rostral ventrolateral medulla (RVLM) decreases blood pressure, heart rate (HR), and sympathetic nerve activity and that these effects are enhanced in stroke-prone spontaneously hypertensive rats (SHRSP). The aim of this study was to determine if an increase in NO production in the RVLM caused by the overexpression of eNOS improves the impaired baroreflex control of HR in SHRSP. We transfected adenovirus vectors encoding eNOS (AdeNOS) into the RVLM of SHRSP or Wistar-Kyoto rats (WKY). Mean arterial pressure and HR were measured by a radio-telemetry system in the conscious state. Reflex changes in HR were elicited by intravenous infusion of either phenylephrine, sodium nitroprusside, or hydralazine at day 7 after the gene transfer. The maximum gain of the baroreflex control of HR was significantly decreased in SHRSP compared with WKY. Overexpression of eNOS in the RVLM of SHRSP improved the impaired maximum gain of the baroreflex control of HR. After treatment with atropine, the maximum gain was still significantly greater in SHRSP in the AdeNOS-transfected group than in the nontransfected group, although it was decreased in both groups. In contrast, after treatment with metoprolol, the maximum gain did not differ between the two groups. These results indicate that an increase in NO production in the RVLM improves the impaired baroreflex control of HR in SHRSP and that these effects may have resulted from a cardiac sympathoinhibitory effect of NO in the RVLM of SHRSP.

Reduced nitric oxide synthase in the brainstem contributes to enhanced sympathetic drive in rats with heart failure.

Recent studies have suggested that central nervous mechanisms are involved in the enhanced sympathetic drive observed in heart failure (HF). Nitric oxide (NO) in the brainstem has been shown to reduce sympathetic nerve activity. The aim of this study was to determine whether the expression of neuronal nitric oxide synthase (nNOS) in the brainstem is reduced in rats with HF. Heart failure was produced by myocardial infarction in Wistar-Kyoto rats (HF group). Hemodynamic and echocardiographic examinations were performed. Western blot analysis for nNOS in the nucleus tractus solitarii (NTS) and the rostral ventrolateral medulla (RVLM) in the brainstem were performed to determine the expression of the nNOS gene in the HF group or sham-operated (control) group. We also performed in situ hybridization for nNOS mRNA and distribution in the brainstem. The expression of nNOS protein in the NTS and the RVLM were reduced in the HF group compared to the control group. The expression of nNOS mRNA in the brainstem was also reduced in the HF group, particularly in the NTS, compared to the control group. Intracisternal injection of NG-monomethyl-L-arginine elicited a smaller pressor response in the HF group than in the control group. These results suggest that reduced nNOS expression in the NTS and the RVLM, and the resulting reduced NO production of these sites, contribute to the enhanced sympathetic drive in HF.