Differential regulation of brown adipose and splanchnic sympathetic outflows in rat: roles of raphe and rostral ventrolateral medulla neurons

1. The medullary premotor neurons determining the sympathetic outflow regulating cardiac function and vasoconstriction are located in the rostral ventrolateral medulla (RVLM). The present study sought evidence for an alternative location for the sympathetic premotor neurons determining the sympathetic nerve activity (SNA) controlling brown adipose tissue (BAT) metabolism and thermogenesis. 2. The tonic discharge on sympathetic nerves is determined by the inputs to functionally specific sympathetic preganglionic neurons from supraspinal populations of premotor neurons. Under normothermic conditions, BAT SNA was nearly silent, while splanchnic (SPL) SNA, controlling mesenteric vasoconstriction, exhibited sustained large-amplitude bursts. 3. The rostral raphe pallidus (RPa) contains potential sympathetic premotor neurons that project to the region of sympathetic preganglionic neurons in the thoracic spinal cord. Disinhibition of neurons in RPa elicited a dramatic increase in BAT SNA, with only a small rise in SPL SNA. 4. Splanchnic SNA was strongly influenced by the baroreceptor reflex, as indicated by a high coherence with the arterial pressure wave, a significant amplitude modulation over the time-course of the cardiac cycle and a marked inhibition of SPL SNA during a sustained increase in arterial pressure. When activated, the bursts in BAT SNA exhibited no correlation with arterial pressure and were not affected by increases in arterial pressure. 5. Because these characteristics and reflex responses in sympathetic outflow have been shown to arise from the on-going or altered discharge of sympathetic premotor neurons, the marked differences between SPL and BAT SNA provide strong evidence supporting the hypothesis that vasoconstriction and thermogenesis (metabolism) are controlled by distinct populations of sympathetic premotor neurons, the former in the RVLM and the latter, potentially, in the RPa.     

Role of nitric oxide on pressor mechanisms within the dorsomedial and rostral ventrolateral medulla in anaesthetized cats

1. The role of nitric oxide (NO) in central cardiovascular regulation and the correlation between NO and glutamate-induced mechanisms is not clear. Microinjection of glutamate (3 nmol/30 nL) into dorsomedial medulla (DM) and rostral ventrolateral medulla (RVLM) increased arterial blood pressure (BP) and sympathetic vertebral nerve activity (VNA). Thus, in the present study, we examined the modulation by NO of glutamate-induced pressor responses in the DM and RVLM of cats. 2. Histochemical methods using nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd) as a marker to stain neurons containing NO synthase (NOS), showed positive findings of NOS in both the DM and RVLM. 3. Microinjection of N(G)-nitro-L-arginine methyl ester (L-NAME), a NOS inhibitor, into the DM or RVLM did not alter resting BP and VNA, but it did cause a dose-dependent attenuation of glutamate-induced pressor responses. Interestingly, the increase in NO levels that resulted from pretreatment with L-arginine (L-Arg) or sodium nitroprusside (SNP) did not alter resting BP and VNA, but still inhibited glutamate-induced pressor responses in the DM and RVLM in a dose-dependent manner. 4. We also examined whether NO modulated the pressor responses induced by activation of different excitatory amino acid receptors. N-Methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (AMPA) were used. Consistent with the results from the initial glutamate studies, we observed that not only L-NAME, but also L-Arg and SNP attenuated pressor responses induced by NMDA and AMPA. No difference was found between the effects of NO on NMDA- and AMPA-induced pressor responses. 5. To investigate the possibility of a loss of agonist selectivity, the effects of D-2-amino-5-phosphonovalerate (D-AP5) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) on AMPA and NMDA responses in the DM were examined. The results showed that CNQX did not alter NMDA-induced pressor responses, while D-AP5 failed to alter AMPA-induced responses. 6. Our results suggest that activation of the glutamate-induced pressor mechanism is regulated by changes in NO levels in the DM and RVLM. This implies that NO may play a permissive role to allow operation of the glutamate-activation mechanism.     

Role of angiotensin II receptors in the regulation of vasomotor neurons in the ventrolateral medulla

1. There is a high density of angiotensin type 1 (AT1) receptors in various brain regions involved in cardiovascular regulation. The present review will focus on the role of AT1 receptors in regulating the activity of sympathetic premotor neurons in the rostral part of the ventrolateral medulla (VLM), which are known to play a pivotal role in the tonic and phasic regulation of sympathetic vasomotor activity and arterial pressure. 2. Microinjection of angiotensin (Ang) II into the rostral VLM (RVLM) results in an increase in arterial pressure and sympathetic vasomotor activity. These effects are blocked by prior application of losartan, a selective AT1 receptor antagonist, indicating that they are mediated by AT1 receptors. However, microinjection of AngII into the RVLM has no detectable effect on respiratory activity, indicating that AT1 receptors are selectively or even exclusively associated with vasomotor neurons in this region. 3. Under normal conditions in anaesthetized animals, AT1 receptors do not appear to contribute significantly to the generation of resting tonic activity in RVLM sympathoexcitatory neurons. However, recent studies suggest that they contribute significantly to the tonic activity of these neurons under certain conditions, such as salt deprivation or heart failure, or in spontaneously hypertensive or genetically modified rats in which the endogenous levels of AngII are increased or in which AT1 receptors are upregulated. 4. Recent evidence also indicates that AT1 receptors play an important role in mediating phasic excitatory inputs to RVLM sympathoexcitatory neurons in response to activation of some neurons within the hypothalamic paraventricular nucleus. The physiological conditions that lead to activation of these AT1 receptor-mediated inputs are unknown. Further studies are also required to determine the cellular mechanisms of action of AngII in the RVLM and its interactions with other neurotransmitters in that region.     

猫头端延髓腹外侧区微量注射内皮素—1对其血压和心率的影响

为了探讨内皮素-1在头端延髓腹外侧区(the rostral ventrolateral medulla, rVLM)对心血管活动的影响。我们使用立体定位技术和微量注射的方法,用15只猫,观察了内皮素-1在该处对动脉血压(AP)、心率(HR)的影响。结果发现,随着内皮素-1剂量的增加,AP和HR也明显地升高和加快。     

Nitric oxide modulates cardiovascular function in the rat by activating adenosine A2A receptors and inhibiting acetylcholine release in the rostral ventrolateral medulla

1. Nitric oxide (NO), a gas transmitter, modulates many physiological processes, including the central regulation of cardiovascular activity. However, the mechanisms underlying the regulation of cardiovascular activity remain relatively unexplored. In the present study, we hypothesized that central NO-dependent sympathetic inhibition is mediated by activation of adenosine A(2A) receptors (A(2A)R) and inhibition of acetylcholine (ACh) release in the rostral ventrolateral medulla (RVLM). 2. L-Arginine (L-Arg; an NO donor; 100 nmol/100 nL) was microinjected into the RVLM of male Sprague-Dawley rats and heart rate variability (HRV) was assessed as an index of cardiac sympathovagal balance. Following microinjection of L-Arg, decreases were seen in mean arterial pressure (MAP), heart rate (HR) and the ratio of the low- to high-frequency components (LF/HF) of HRV. Pretreatment of rats with SCH58261 (40 pmol/60 nL into the RVLM), a competitive antagonist of the A(2A) R, attenuated these effects. 3. Western blot analysis and ELISA revealed that adenosine and A(2A)R levels increased in the RVLM following L-Arg microinjection, whereas ACh and muscarinic M(1) receptor levels decreased significantly, in parallel with the cardiovascular responses to L-Arg microinjection. The decrease in ACh levels was abolished by SCH58261 pretreatment. 4. Microinjection of N(G)-nitro-L-arginine methyl ester (a non-selective inhibitor of NO synthase; 15 nmol/100 nL) into the RVLM significantly increased MAP, HR and sympathetic activity, as evidenced by HRV (LF, HF and the LF/HF ratio were all increased). 5. The results indicate that the central NO/NO synthase system in the RVLM may modulate cardiovascular activity by activating the A(2A)R, which subsequently inhibits activation of the muscarinic M(1) receptor.     

Modulation of pressor response to muscle contraction via monoamines following AMPA-receptor blockade in the ventrolateral medulla

We hypothesized that cardiovascular responses to static muscle contraction are mediated via changes in extracellular concentrations of monoamines (norepinephrine, dopamine and serotonin) following the administration of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, an AMPA-receptor antagonist) into the rostral (RVLM) or caudal (CVLM) ventrolateral medulla. For the RVLM experiments (n= 8), a 2-min static muscle contraction increased the mean arterial pressure (MAP) and heart rate (HR) by 23 +/- 2 mmHg and 28 +/- 8 bpm, respectively. During this contraction, the concentrations of norepinephrine, dopamine, and serotonin within the RVLM increased by 278 +/- 52%, 213 +/- 23%, and 232 +/- 24%, respectively. Microdialysis of CNQX (1.0 microM) for 30 min into the RVLM attenuated the increases in MAP and HR ( 11 +/- 2 mmHg and 14 +/- 5 bpm) without a change in developed muscle tension. The levels of norepinephrine, dopamine, and serotonin within the RVLM were also attenuated. In contrast, microdialysis of CNQX into the CVLM (n= 8) potentiated the contraction-evoked responses in MAP ( 21 +/- 2 vs 33 +/- 5 mmHg) and HR ( 25 +/- 5 vs 46 +/- 8 bpm) without any effect on the monoamine levels within the CVLM region. These results suggest that AMPA-receptor blockade within the RVLM and CVLM has opposing effects on cardiovascular responses during static muscle contraction. In addition, such receptor blockade modulates extracellular concentrations of monoamines within the RVLM but not in the CVLM. These results provide evidence that AMPA receptors within the ventrolateral medulla play a role in exercise pressor reflex.     

Metabotropic neurotransmission and integration of sympathetic nerve activity by the rostral ventrolateral medulla in the rat

1. Cardiovascular sympathetic nerve activity at rest is grouped into waves, or bursts, that are generally, although not exclusively, related to the heart rate and to respiration. In addition, activity is also generated in response to central commands and to environmental stimuli. 2. Responsibility for the integration of all these different elements of sympathetic activity rests with pre-motoneurons in the rostral ventrolateral medulla oblongata. These pre-motoneurons are glutamatergic and spinally projecting where they form synapses with sympathetic preganglionic neurons. 3. Pre-motoneurons also contain and presumably release, neurotransmitters other than glutamate, including amines and neuropeptides that act on metabotropic receptors with long-term effects on cell function. 4. Similarly, in the rostral ventrolateral medulla oblongata the pre-motoneurons are mainly regulated by excitatory influences from glutamate and inhibitory influences from gamma-aminobutyric acid (GABA). Major focuses of recent studies are the interactions between non-glutamatergic and GABAergic systems and reflexes that regulate the activity of the sympathetic nervous system. 5. The results indicate that neurotransmitters acting at metabotropic receptors selectively affect different reflexes in the rostral ventrolateral medulla. It is suggested that this differential activation or attenuation of reflexes by different neurotransmitters is a mechanism by which the organism can fine-tune its responses to different homeostatic requirements.     

Ipsilateral but not contralateral blockade of excitatory amino acid receptors in the caudal ventrolateral medulla inhibits aortic baroreceptor reflex in rats

Summary The caudal ventrolateral medulla (CVLM) contains vasodepressor neurons which, when activated, decrease vasomotor tone. To investigate whether excitatory amino acid receptors in the CVLM of the rat are involved in mediation of the aortic baroreceptor reflex, we microinjected amino acid antagonists unilaterally into the CVLM and examined their effects on the depressor response to electrical stimulation of the aortic nerve which contains mainly baroreceptor afferent fibers in rats. Male Wistar rats were anaesthetized with urethane, paralyzed and artificially ventilated. To block reflex vagal effects, methylatropine (1 mg/kg) was given intravenously. Kynurenate (227 ng), an excitatory amino acid antagonist, injected ipsilaterally but not contralaterally into the CVLM markedly inhibited the depressor response to aortic nerve stimulation, while both injections produced a similar small increase in basal blood pressure. Muscimol (1 ng), a GABA receptor agonist, injected ipsilaterally into the CVLM partly inhibited the baroreflex response, while it produced a moderate increase in basal blood pressure. 2-Amino-5-phosphonovalerate (APV) (10 ng), a N-methyl-d-aspartate (NMDA) receptor antagonist, and MK-801 (30 ng), a NMDA receptor channel blocker, partly inhibited the baroreflex response. MK-801 (30 ng) injected into the CVLM reduced the depressor response to the NMDA receptor agonist NMDA (0.3 ng) but not to the quisqualate receptor agonist quisqualate (0.1 ng) and the kainate receptor agonist kainate (0.1 ng), while kynurenate (227 ng) inhibited the depressor response to all three excitatory amino acid receptor agonists. These findings provide further evidence for the presence of excitatory amino acid receptors involved in mediating the aortic baroreceptor reflex in the rat CVLM. It appears that neurons other than the vasodepressor neurons in the CVLM, at least in part, play a role in transmitting the aortic baroreceptor reflex. In addition, both NMDA and non-NMDA receptors may be responsible for the mediation of the reflex. Send offprint requests to T. Kubo at the above address     

氯胺酮对大鼠头端延髓腹外侧区前交感神经元的作用(英文)

目的:研究氯胺酮在中枢交感心血管活动中的调节作用。方法:在25只氨基甲酸乙酯麻醉、三碘季铵酚制动并人工通气的雄性SD大鼠中,共细胞外记录到32个头端延髓腹外侧区前交感神经元的自发放电,这些神经元具有压力敏感性和向脊髓投射的特点。观察选择性NMDA受体拮抗剂氯胺酮对前交感神经元放电的影响。结果:静脉注射不同剂量的氯胺酮(3,6,12mg/kg)能增加RVLM前交感神经元的放电频率,同时能阻断这些神经元的压力敏感性,且具有剂量依赖性的特点。结论:氯胺酮通过阻断RVLM前交感神经元压力感受反射的紧张性抑制,从而调节交感心血管活动。     

Differential contributions of NOS isoforms in the rostral ventrolateral medulla to cardiovascular responses associated with mevinphos intoxication in the rat

The organophosphate poison mevinphos (Mev) elicits cardiovascular responses via nitric oxide (NO) produced on activation of M2 muscarinic receptors (M2R) in the rostral ventrolateral medulla (RVLM), where sympathetic vasomotor tone originates. This study further evaluated the contribution of nitric oxide synthase (NOS) isoforms at the RVLM to this process, using adult Sprague-Dawley rats. Bilateral co-microinjection into the RVLM of the selective NOS I inhibitor (250 pmol), 7-nitroindazole or N(omega)-propyl-L-arginine antagonized the initial sympathoexcitatory cardiovascular responses to Mev (10 nmol). Co-administration of a selective NOS II inhibitor, N6-(1-iminoethyl)-L-lysine (250 or 500 pmol) further enhanced these cardiovascular responses and reversed the secondary sympathoinhibitory actions of Mev. A potent NOS III inhibitor, N5-(1-iminoethyl)-L-ornithine (46 or 92 nmol) was ineffective. We also found that M2R co-localized only with NOS I- or NOS II-immunoreactive RVLM neurons. Furthermore, only NOS I or II in the ventrolateral medulla exhibited an elevation in mRNA or protein levels during the sympathoexcitatory phase, with further up-regulated synthesis of NOS II during the sympathoinhibitory phase of Mev intoxication. We conclude that whereas NOS III is not engaged, NO produced by NOS I and II in the RVLM plays, respectively, a sympathoexcitatory and sympathoinhibitory role in the cardiovascular responses during Mev intoxication.     

RU486对硫酸皮质酮引起的头端延髓腹外侧区心血管神经元作用的影响

目的研究糖皮质激素（ＧＣ）的非基因组机制在交感神经活动调节中的作用。方法细胞外记录氨基甲酸乙酯麻醉的ＳＤ大鼠头端延髓腹外侧区（ＲＶＬＭ）被鉴定的心血管神经元的自发放电,观察微电泳硫酸皮质酮（Ｏ３ＲＴ对心血管神经元活动的影响,及其 ＧＣ受体拮抗剂 ＲＵ ４８６对ＣＯＲＴ导致神经元作用的影响。结果在ＲＶＬＭ共记录到３３个心血管神经元,微电泳硫酸皮质酮（ＣＯＲＴ）后２５（７６％）个神经元放电迅速加快,且具有剂量依赖性,余８个（２７％）心血管神经元自发放电没有变化;其中被ＣＯＲＴ兴奋的１２个单位微电泳ＲＵ４８６（糖皮质激素受体阻断剂）后神经元的基础放电没有明显变化（Ｐ＞０．０５）,但能部分（９个单位）或完全（３个单位）阻断硫酸皮质酮导致的兴奋作用。结论Ｏ３ＲＴ对ＲＶＬＭ心血管神经元具有快速的兴奋作用,ＲＵ４８６并不改变ＲＶＬＭ心血管神经元的基础活动,但能部分或完全阻断ＣＯＲＴ导致的神经元兴奋作用。     

Area postrema and sympathetic nervous system effects of vasopressin and angiotensin II

1. Precise control over the cardiovascular system requires the integration of both neural and humoral signals related to blood volume and blood pressure. Humoral signals interact with neural systems, modulating their control over the efferent mechanisms that ultimately determine the level of pressure and volume. 2. Peptide hormones such as angiotensin (Ang)II and arginine vasopressin (AVP) act through circumventricular organs (CVO) to influence cardiovascular regulation. 3. The area postrema (AP), a CVO in the brainstem, mediates at least some of the central actions of these peptides. Vasopressin appears to act in the AP to cause sympathoinhibition and a shift in baroreflex control of the sympathetic nervous system (SNS) to lower pressures. These effects of AVP and the AP appear to be mediated by alpha2-adrenoceptor and glutamatergic mechanisms in the nucleus tractus solitarius. 4. In contrast to AVP AngII has effects in the AP to blunt baroreflex control of heart rate and cause sympathoexcitation. The effects of chronic AngII to increase activity of the SNS may be due to AP-dependent activation of neurons in the rostral ventrolateral medulla.     

Contribution of peroxynitrite to fatal cardiovascular depression induced by overproduction of nitric oxide in rostral ventrolateral medulla of the rat

We evaluated the contribution of peroxynitrite to the fatal cardiovascular depression induced by overproduction of nitric oxide (NO) after activation of inducible NO synthase (iNOS) in the rostral ventrolateral medulla (RVLM), the origin of sympathetic vasomotor tone. In Sprague-Dawley rats maintained under propofol anesthesia, microinjection of E. coli lipopolysaccharide (LPS) bilaterally into the RVLM elicited significant hypotension, bradycardia, reduction in sympathetic vasomotor tone and mortality. There was also a discernible elevation of iNOS expression in the ventrolateral medulla, followed by a massive production of nitrotyrosine, an experimental index for peroxynitrite. Co-administration bilaterally into the RVLM of the selective iNOS inhibitor, S-methylisothiourea (50, 100 or 250 pmol), an active peroxynitrite decomposition catalyst, 5,10,15,20-tetrakis- (N-methyl-4'-pyridyl)-porphyrinato iron (III) (10 or 50 pmol), a peroxynitrite scavenger, L-cysteine (5, 50 or 100 pmol), or a superoxide dismutase mimetic, Mn(III)-tetrakis-(4-benzoic acid) porphyrin (1 or 10 pmol), significantly prevented mortality, reduced nitrotyrosine production and reversed the NO-induced cardiovascular suppression after application of LPS into the RVLM. We conclude that the formation of peroxynitrite by a reaction between superoxide anion and NO is primarily responsible for the fatal cardiovascular depression induced by overproduction of NO after activation of iNOS at the RVLM.     

The baroreflex and beyond: control of sympathetic vasomotor tone by GABAergic neurons in the ventrolateral medulla

1. Barosensitive, bulbospinal neurons in the rostral ventrolateral medulla (RVLM), which provide the major tonic excitatory drive to sympathetic vasomotor neurons, are prominently inhibited by GABA. 2. A major source of the GABAergic inhibition to presympathetic RVLM neurons arises from an area immediately caudal to the RVLM, known as the caudal ventrolateral medulla (CVLM). 3. Arterial baroreceptor afferents projecting to the nucleus tractus solitarius (NTS) provide a major tonic excitatory input to GABAergic CVLM neurons. These CVLM cells are a critical component for baroreflex-mediated changes in presympathetic RVLM neuronal activity, sympathetic nerve activity (SNA) and arterial pressure (AP). 4. Some GABAergic CVLM neurons are tonically activated by inputs independent of arterial baroreceptors or the NTS, providing a GABAergic-mediated inhibition of the presympathetic RVLM neurons that is autonomous of baroreceptor inputs. 5. GABAergic CVLM neurons appear to play two distinct, yet important, roles in the regulation of sympathetic vasomotor tone and AP. They dampen immediate changes in AP via the baroreflex and tonically inhibit the activity of the presympathetic RVLM neurons by baroreceptor-independent mechanisms. This baroreceptor-independent, GABAergic inhibition of presympathetic RVLM neurons may play an important role in determining the long-term level of sympathetic vasomotor tone and AP.     

Effect of adrenotensin on cell proliferation is mediated by angiotensin II in cultured rat mesangial cells

Aim： Both adrenomedullin （ADM） and adrenotensin （ADT） are derived from the same propeptide precursor, and both act as circulating hormones and local paracrine mediators with multiple biological activities. Compared with ADM, little is known about how ADT achieves its functions. In the present study, we investigated the effect of ADT on cell proliferation and transforming growth factor-β（TGF-β） secretion in cultured renal mesangial cells （MCs） and determined whether angiotensin II （Ang II） was involved in mediating this process. Methods： Cell proliferation was measured by bromodeoxyuridine （BrdU） incorporation assay, Ang II levels were assayed using an enzyme immunoassay, and real time PCR was used to measure Ang II type 1 （AT1） receptor, Ang II type 2 （AT2） receptor, angiotensinogen （AGT）, renin, angiotensin converting enzyme （ACE） and TGF-β1 mRNA levels. TGF-β1 and collagen type IV protein levels in cell media were measured using enzyme-linked immunoassays. Results： ADT treatment induced cell proliferation in a concentration-dependent manner; it also increased the levels of TGF-β1 mRNA and protein as well as collagen type IV excretion by cultured MCs. ADT treatment increased renin and AGT mRNAs as well as Ang II protein, but did not affect the ACE mRNA level. ADT up-regulated angiotensin AT1 receptor mRNA, but not that of the AT2 receptor. The angiotensin AT1 receptor antagonist Iosartan blocked the effects of ADT-induced cell proliferation, TGF-β1 and collagen type IV synthesis and secretion. Conclusion： ADT has a stimulating role in cell proliferation in cultured MCs. Increases in the levels of Ang II and the AT1 receptor after ADT treatment mediate the stimulating effects of ADT on cell proliferation and extracellular matrix synthesis and secretion.     

Phasic cardiovascular responses to mevinphos are mediated through differential activation of cGMP/PKG cascade and peroxynitrite via nitric oxide generated in the rat rostral ventrolateral medulla by NOS I and II isoforms

The organophosphate insecticide mevinphos (Mev) acts on the rostral ventrolateral medulla (RVLM), where sympathetic vasomotor tone originates, to elicit phasic cardiovascular responses via nitric oxide (NO) generated by NO synthase (NOS) I and II. We evaluated the contribution of soluble guanylyl cyclase (sGC)/cyclic guanosine monophosphate (cGMP)/protein kinase G (PKG) cascade and peroxynitrite in this process. PKG expression in ventrolateral medulla of Sprague-Dawley rats manifested an increase during the sympathoexcitatory phase (Phase I) of cardiovascular responses induced by microinjection of Mev bilaterally into the RVLM that was antagonized by co-administration of 7-nitroindazole or Nomega-propyl-L-arginine, two selective NOS I inhibitors or 1-H-[1,2,4]oxadiaolo[4,3-a]quinoxalin-1-one (ODQ), a selective sGC antagonist. Co-microinjection of ODQ or two PKG inhibitors, KT5823 or Rp-8-Br-cGMPS, also blunted the Mev-elicited sympathoexcitatory effects. However, the increase in nitrotyrosine, a marker for peroxynitrite, and the sympathoinhibitory circulatory actions during Phase II Mev intoxication were antagonized by co-administration of S-methylisothiourea, a selective NOS II inhibitor, Mn(III)-tetrakis-(4-benzoic acid) porphyrin, a superoxide dismutase mimetic, 5,10,15,20-tetrakis-N-methyl-4'-pyridyl)-porphyrinato iron (III), a peroxynitrite decomposition catalyst, or L-cysteine, a peroxynitrite scavenger. We conclude that sGC/cGMP/PKG cascade and peroxynitrite formation may participate in Mev-induced phasic cardiovascular responses as signals downstream to NO generated respectively by NOS I and II in the RVLM.     

RENAL SYMPATHETIC BAROREFLEX EFFECTS OF ANGIOTENSIN II INFUSIONS INTO THE ROSTRAL VENTROLATERAL MEDULLA OF THE RABBIT

1. The effects of local infusion of angiotensin II (AII) into the rostral ventrolateral medulla (RVLM) pressor area on the renal sympathetic baroreflex were compared with the excitatory amino acid glutamate in urethane anaesthetized rabbits with chronically implanted renal nerve electrodes. Baroreflex blood pressure-renal nerve activity curves were obtained by intravenous infusion of phenylephrine and nitroprusside before and after treatments. 2. Infusion of 4 pmol/min of All into the RVLM increased blood pressure by 12 ± 2 mmHg and transiently increased resting sympathetic nerve activity. The renal sympathetic baroreflex curves were shifted to the right. The upper plateau of the sympathetic reflex increased by 29 ± 8% (n= 6, P < 0.025). 3. Infusions of glutamate into the RVLM, at a dose which was equipressor to that of AII, also increased resting renal sympathetic nerve activity. In contrast to AII, this increase was maintained throughout the infusion. Glutamate shifted the reflex curve to the right and increased the upper plateau of the sympathetic reflex by 44 ± 5% without affecting the lower plateau. 4. These results support the suggestion that AII can act at the level of the RVLM pressor area to facilitate baroreflex control of renal sympathetic activity in a similar fashion to that produced by fourth ventricular administration. 5. Thus the RVLM is a likely candidate site for modulation of the renal sympathetic baroreflex. The similarity of the actions of AII to those of glutamate suggest that it may directly excite sympathetic vasomotor cells in this region.     

Inhibitory effect of reactive oxygen species on angiotensin I-converting enzyme (kininase II)

1. Somatic angiotensin I-converting enzyme (ACE) is a protein that contains two similar domains (N- and C-terminal), each possessing an active site. We have examined the effects of a generator of hydroxyl radicals (g*OH: 2,2'-azo-bis(2-amidinopropane)) and hydrogen peroxide (H2O2) on ACE using an in vitro approach. 2. The generator of hydroxyl radicals inactivated ACE in a time (2-6 h)- and concentration (0.3-3 mmol/L)-dependent manner at 37 degrees C. When ACE was coincubated for 4 h with g*OH (3 mmol/L), its activity decreased by 70%. Addition of dimethylthiourea or mannitol + methionine, two *OH scavengers, resulted in a significant protection of ACE activity. Mercaptoethanol and dithiotreitol, two thiol-reducing agents, also efficiently protected ACE activity. 3. The hydrolysis of two natural and domain-specific substrates was explored. The hydrolysis of angiotensin I, preferentially cleaved by the C-domain, was significantly inhibited (57-58%) after 4 h exposure to g*OH (0.3-1 mmol/L). Under the same conditions of exposure, the hydrolysis of N-acetyl-Ser-Asp-Lys-Pro, a specific substrate for the N-domain, was only slightly inhibited by 1 mmol/L g*OH. 4. Hydrogen peroxide, another source of *OH, was used. After exposure to H2O2 (3 mmol/L; 4 h), an 89% decrease in ACE activity was observed. Pretreatment with the iron chelator deferoxamine (1 mmol/L) attenuated H2O2-mediated ACE inactivation, demonstrating that the effect of H2O2 was partly due to its conversion into *OH (Fenton reaction). 5. In summary, our findings demonstrate that g*OH and H2O2 inhibit ACE activity and suggest a preferential action of g*OH on the C-domain of the enzyme.     

槲皮素对血管紧张素Ⅱ致培养乳鼠心肌细胞肥大的抑制作用

目的:研究槲皮素(Quercetin,Que)对血管紧张素Ⅱ(Aug Ⅱ)诱发培养乳鼠心肌细胞肥大的抑制作用及机制。方法:分别用[~3H]胸苷、[~(14)C]尿苷和[~3H]酪氨酸标记测定DNA、RNA和蛋白质合成;用Lowry法测定蛋白质含量;用组蛋白ⅢS、[γ-~(32)P]ATP与蛋白激酶C(PKC)酶液一起保温测定PKC活性;用聚谷氨酸·酪氨酸(4:1)多肽、[γ-~(32)P]ATP与酪氨酸蛋白激酶(TPK)酶液一起保温测TPK活性。结果:Aug Ⅱ作用于心肌细胞24h后,心肌细胞总蛋白含量明显增加(P<0.01),[~(14)C]尿苷和[~3H]酪氨酸掺入量明显增加(P<0.01),而[~3H]胸苷掺入量未见增加(P>0.05);Aug Ⅱ作用30min后,心肌细胞PKC和TPK活性明显增加。Que(1-100μmol/L)能剂量依赖性地抑制Ang Ⅱ所致心肌细胞总蛋白含量、[~(14)C]尿苷和[~3H]酪氨酸掺入量、PKC及TPK活性的增加。结论:Que可抑制Aug Ⅱ致培养乳鼠心肌细胞肥大,该作用与抑制PKC及TPK活性有关。