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.

Abstract-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 ␤-galactosidase (Ad␤gal) 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 Ad␤gal transfection. Urinary norepinephrine excretion was significantly higher in AdiNOS-transfected rats than in Ad␤gal-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 Ad␤gal-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. Key Words: nitric oxide synthase Ⅲ blood pressure Ⅲ sympathetic nervous system Ⅲ oxidative stress Ⅲ gene transfer N itric oxide (NO) in the central nervous system (CNS), including the brain stem and hypothalamus, plays an important role in the regulation of blood pressure via the sympathetic nervous system. [1][2][3][4][5][6][7] In general, NO in the CNS inhibits sympathetic nerve activity, thereby reducing blood pressure. [2][3][4] The rostral ventrolateral medulla (RVLM) in the brain stem contains sympathetic premotor neurons responsible for maintaining the tonic excitation of sympathetic preganglionic neurons involved in cardiovascular regulation. 8 -10 The functional integrity of the RVLM is essential for the maintenance of basal vasomotor tone, and RVLM abnormalities might be related to the pathophysiology of hypertension 11-14 and heart failure. 15,16 Recently, we developed a technique for adenovirusmediated endothelial NO synthase (eNOS) gene transfer into the RVLM 11,14,[17][18][19] or the nucleus tractus solitarii (NTS) 20,21 in vivo. An increase in NO production in the RVLM induced by eNOS overexpression decreases blood pressure and heart rate (HR) by inhibiting the sympathetic nervous system. 11,14,19 In that series of studies, we used eNOS instead of neuronal NO synthase (nNOS), which is normally abundant...

Abstract-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 (meanϮSE age, 23Ϯ2 years; 24 men and 7 women). After oral administration of aspirin (486 mg), we infused N G -monomethyl-L-arginine (8 mol/min for 5 minutes) into the brachial artery. We used tetraethylammonium chloride (TEA, 1 mg/min for 20 minutes), a K Ca channel blocker, as an EDHF inhibitor, and nicorandil as a direct K ϩ channel opener. TEA significantly reduced FBF (PϽ0.05) 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, nϭ8) and bradykinin (12.5, 25, 50, and 100 ng/min, nϭ8; both PϽ0.001), whereas it did not affect the FBF increase in response to acetylcholine (4,8,16, and 32 g/min, nϭ8), sodium nitroprusside (0.4, 0.8, 1.6, and 3.2 g/min, nϭ8), or nicorandil (0.128, 0.256, 0.512, and 1.024 mg/min, nϭ8). 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. The major vasorelaxive factors involved in this role are nitric oxide (NO), prostacyclin (PGI 2 ), and endothelium-derived hyperpolarizing factor (EDHF). 1,2 Compared with the well-documented roles of NO and PGI 2 , the role of EDHF in modulating vascular smooth muscle contraction is not fully understood, although Ͼ10 years have passed since the first reports of EDHF. 3,4 This is partly because the exact nature of EDHF remains to be identified. The EDHF candidates include epoxyeicosatrienoic acids, which are metabolites of cytochrome P-450 monooxygenase 5,6 ; K ϩ 7 ; gap junctions 8 ; and hydrogen peroxide. 9,10 Thus, more than one EDHF might exist, and the contribution of each EDHF to endothelium-dependent relaxation might vary, depending on the species tested and the vessels used. 1,2 In general, the hyperpolarizing mechanism of EDHF is considered to be mediated by Ca 2ϩ -activated K ϩ (K Ca ) channels on vascular smooth muscle. [11][12][13][14] Recent animal studies from our laboratories indicate that the role of EDHF in small vessels is important and is impaired with aging. 15,16 These results suggest the physiologic importance of EDHF for modulating vascular smooth muscle tone. Furthermore, animal studies indicate that EDHF-mediated relaxation is impaired in hypertension, 17,18 hypercholesterolemia, 19 and diabetes mellitus. 20 The existence and importance of EDHF have been demonstrated in various isolated human arteries. 10,16,21 For example, EDHF-mediated vascular responses are observed in gastroepiploic and distal mesenteric arteries. 16 Bradykinin-induced vasodilatation of human coronary microvessels is largely due to...

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, nϭ26) and an age-matched control group (nϭ26). 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

Abstract-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. Key Words: genes Ⅲ nitric oxide Ⅲ sympathetic nervous system Ⅲ brain Ⅲ baroreflex I t is well established that the central nervous system plays an important role in controlling arterial baroreflex function. 1,2 The major baroreceptor reflex pathway exits in the brain stem, such as the nucleus tractus solitarii (NTS), the caudal ventrolateral medulla (CVLM), and the rostral ventrolateral medulla (RVLM). 1,2 In particular, the RVLM contains sympathetic premotor neurons responsible for maintaining sympathetic outflow. 3 It is also well known that the baroreceptor reflex control of heart rate is impaired in various animal models of hypertension 4 -9 and in patients with hypertension. 10 Reduced arterial baroreceptor sensitivity has been shown to be responsible for this impaired baroreflex function. 4 -8 However, recent studies have suggested that central nervous mechanisms may also be involved in the impaired baroreceptor reflex function in hypertension. 9,11 There is considerable evidence that neuronal nitric oxide synthase (nNOS) exists within the brain stem, including the RVLM and NTS, 12 and plays an important role in regulating sympathetic nerve activity. [13][14][15][16] At resting conditions, microinjection studies into the RVLM with NO donors or NOS inhibitors have produced conflicting results, including both pressor or depressor responses, and explanation of these results remains to be elucidated. 16 -22 It is possible that anesthesia...