Decreased renal haemodynamic response to inhibition of nitric oxide synthase in subtotally nephrectomized rats

To assess the renal haemodynamic response to manipulations of the nitric oxide (NO) system, we examined subtotally nephrectomized (SNX) rats and control rats (CON) 28 days after their operation. Bolus infusions of the NO synthase inhibitor N ^G-nitro-l-arginine (l-NA) were given intravenously at doses of 2 mg/kg and 10 mg/kg. Blood pressure was measured intra-arterially, glomerular filtration rate was measured by inulin clearance and fractional changes in renal blood flow (RBF) were determined by a Doppler flow probe. Both doses of l-NA caused a similar and dose dependent increase in mean blood pressure in both SNX and CON rats. In contrast, the decrease in RBF and the increase in the renovascular resistance index (RVRI) was less in SNX rats as compared to CON rats (RBF = –70.1±2.2% of baseline vs –52.7±5.2%, P<0.01; RVRI = +177±9% of baseline vs +243±24%, P<0.05). These changes were not affected by autonomic blockade (hexamethonium), or by blockade of the angiotensin II receptor (Losartan). The exogenous NO donor sodium nitroprusside (0.5 and 1.5 g · kg^–1 · min^–1) lowered mean blood pressure to a similar degree in SNX and CON rats; in contrast, RVRI decreased less in SNX rats (86.9±9.2% of baseline) than in CON rats (68.2±4.6%, P<0.05). We conclude that the reaction of the renal vasculature to manipulations of the NO system is altered in the SNX rats. The data suggest that in the remnant kidney, renovascular resistance is less dependent on endogenous NO and the vascular bed is less sensitive to exogenous NO.     

诱导型一氧化氮合酶与Dahl-盐敏感大鼠动脉血压的调节

目的和方法:为探讨诱导型一氧化氮合酶 (iNOS)在血液动力学调控中的作用,本研究通过慢性血液动力学实验观察了静脉输入诱导型一氧化氮合酶 (iNOS)抑制剂aminogunidine(AG)对大鼠平均动脉压的影响,并测定了一氧化氮 (NO)终产物NO₂及NO₃含量(UNOx)以及iNOS活性。结果:1.iNOS特异抑制剂AG能明显放大高钠引起的Dahl盐敏感大鼠(DS)的血压上升效应;2.高NaCl输入在导致的DS大鼠血压升高的同时,能引起iNOS活性及UNOx的明显升高。结论:iNOS对DS大鼠具有重要的血液动力学调节作用。     

诱导型一氧化氮合酶与动脉血压的调节

目的:探讨诱导型一氧化氮合酶在血液动力学调控中的作用。方法:本实验所用动物为健康、雄性、Dahl 盐敏感(DS)及Dahl盐不敏感(DR)大鼠,体重(190±4) g。通过慢性血液动力学实验观察静脉输入诱导型一氧化氮合酶(iNOS)抑制剂AG对大鼠平均动脉压的影响。此外,本实验还测定了一氧化氮(NO)终产物NO₂^-及NO₃^-含量以及钙依赖及钙不依赖的NOS活性以了解iNOS的功能。结果:(1)iNOS特异抑制剂AG对正常血压(包括高盐或低盐输入的Dahl盐抵抗大鼠及低盐输入的Dahl盐敏感大鼠)没有明显影响,但能明显放大高钠引起的DS大鼠的血压上升效应;(2)高盐在导致的DS大鼠血压升高的同时,能引起iNOS活性的明显升高。结论:iNOS是参与血液动力学调控的重要组成部分,尤其是在血压处于较高水平时,iNOS具有不容忽视的调节作用。     

用ESR检测兔心肌顿抑时一氧化氮的动态变化

目的：用顺磁共振技术（ESR）测定兔在心肌缺血再灌注过程中心肌顿抑时，血液中一氧化氮（NO）动态变化。方法：结扎前降支制成心肌缺血-再灌注模型，经颈动脉左心室插管，多导生理仪记录左心室最大上升速率（dp/dt_max）、心室舒张末压力、动脉血压、心率等血液动力学指标。分别于缺血前、缺血5 min、10 min，再灌注5 min、10 min、30 min、60 min、90 min、120 min各时点取静脉血1 mL，在电子自旋共振仪记录NO波谱，测定NO水平。结果：在再灌注5 min、120 min时，NO浓度明显高于缺血前[(23.4±4.8) mm vs (12.0±0.5) mm，(21.4±1.8) mm vs (12.0±0.5) mm，P<0.01]。心肌收缩功能在缺血5 min时已经开始受损[(4965±295.6) mmHg/s vs (3967±315.3) mmHg/s，与缺血前比较P<0.01]，但是在再灌注5 min时明显低于缺血5 min时[(3327±120.4) mmHg/s vs(3967±315.3) mmHg/s，P<0.05]。结论：再灌注早期NO升高而心肌收缩力下降，提示NO对早期缺血再灌时心肌顿抑有加重作用。     

Modulation of extracellular glutamate and pressor response to muscle contraction during NMDA-receptor blockade in the rostral ventrolateral medulla

Recently our laboratory demonstrated increases in extracellular glutamate concentrations within the rostral ventrolateral medulla (RVLM) during static muscle contraction (Caringi, D.C., Maher, T., Chaiyakul, P., Asmundsson, G., Ishide, T., Ally, A. Pflügers Arch. Eur. J. Physiol., 435:465-471, 1998). In this study, we determined effects of microdialyzing D(-)2-amino-7-phosphonohepatanoic acid (AP-7), an NMDA-receptor antagonist, into the RVLM on changes in mean arterial pressure (MAP), heart rate (HR), and extracellular glutamate levels during muscle contraction in anesthetized rats. Bilateral placements of microdialysis probes into the RVLM were verified by perfusing L-glutamate and obtaining a pressor response. Muscle contraction for 2 min, increased MAP and HR by 22+/-4 mmHg and 28+/-5 bpm, respectively. Extracellular glutamate as determined by microdialysis increased from 0.8+/-0.2 to 6.3+/-1.2 ng/5 microl. Microdialysis of AP-7 (1.0 microM) for 30 min inhibited contraction-evoked MAP and HR responses (10+/-3 mmHg and 13+/-3 bpm) and attenuated increases in glutamate during muscle contraction. Developed tensions did not differ during contractions before and after AP-7. Results demonstrate that NMDA-receptor blockade in the RVLM inhibits cardiovascular responses during static muscle contraction via a reduction in extracellular glutamate levels.     

Blood pressure, heart rate, and behavioral responses to psychological "novelty" stress in freely moving rats

We developed a new model of psychological "open-field" stress in freely moving rats. Blood pressure and heart rate of the rats were measured by radiotelemetry and behavior analyzed by video tracking software. Open-field exposure induced marked increases in blood pressure and heart rate. Repeated daily exposure induced pressor responses that were slightly higher on Day 4 when compared to Day 1. Pretreatment with the beta1-adrenoceptor antagonist atenolol inhibited the tachycardia whereas the ganglion blocker pentolinium inhibited the pressor response, indicating involvement of the sympathetic nervous system. Pretreatment with diazepam prevented the novelty stress-induced pressor response and reduced the tachycardia. These results show that the psychological stress of exposing rats to an open field induces marked cardiovascular effects that are mediated by sympathetic hyperactivity. This model is unique in that it focuses on psychological stress and allows concomitant measurement of blood pressure, heart rate, and behavior in freely moving rats.     

Vasopressin release during endotoxaemic shock in mice lacking inducible nitric oxide synthase

We tested the hypothesis that nitric oxide (NO) arising from the action of inducible nitric oxide synthase (iNOS) is responsible for the deficiency in vasopressin (AVP) release and consequent hypotension during endotoxaemic shock. Wild-type (WT) and iNOS knockout mice (iNOS^–/–) were given either saline or Escherichia coli lipopolysaccharide (LPS, 1.0 mg/kg i.v., final volume 0.03 ml). Mean arterial blood pressure (MAP) was measured and plasma AVP levels determined before and after LPS or saline injection. In WT mice, MAP was significantly lower 2 h after LPS administration and remained low for the remainder of the 6-h observation period. AVP plasma levels were increased at the 2nd and 4th h of the experiment, returning thereafter to basal levels. Conversely, LPS injection in iNOS iNOS^–/– mice elicited a sustained increase in plasma AVP concentration and attenuated the fall in blood pressure. These data indicate that NO arising from the iNOS plays an important inhibitory role in AVP release during endotoxaemia and may be responsible for the hypotension occurring during this vasodilatory shock.     

Hypoxia-induced Fos expression in neurons projecting to the pressor region in the rostral ventrolateral medulla

Previous studies in anaesthetized animals have shown that the hypoxia-induced increase in sympathetic vasomotor activity is largely dependent on synaptic excitation of sympathoexcitatory pressor neurons in the rostral part of the ventrolateral medulla. The primary aim of this study was to determine, in conscious rabbits, the distribution of neurons within the brain that have properties characteristic of interneurons conveying excitatory inputs to the rostral ventrolateral medullary pressor region in response to systemic hypoxia. In a preliminary operation, a retrogradely-transported tracer, fluorescent-labelled microspheres, was injected into the physiologically-identified pressor region in the rostral ventrolateral medulla. After a waiting period of one to two weeks, the conscious rabbits were subjected to moderate hypoxia (induced by breathing 10% O₂ in N₂) for a period of 60 min. Control groups of animals were exposed to room air or to mild hypoxia (12% O₂ in N₂). Moderate hypoxia resulted in a modest hypertension of approximately 15 mmHg, and in the expression of Fos (a marker of neuronal activation) in many neurons in the nucleus tractus solitarius, the rostral, intermediate and caudal parts of the ventrolateral medulla, the Kölliker–Fuse nucleus, locus coeruleus, subcoeruleus and A5 area in the pons as well as in several midbrain and forebrain regions, including the periaqueductal grey in the midbrain and the paraventricular, supraoptic and arcuate nuclei in the hypothalamus. Fos expression was also observed in these regions in rabbits subjected to mild hypoxia or normoxia, but it was much reduced compared to rabbits subjected to moderate hypoxia. Approximately half of the neurons in the ventrolateral medulla, 27% of neurons in the nucleus tractus solitarius, and 49–81% of neurons in the locus coeruleus, sub-coeruleus and A5 area that expressed Fos following moderate hypoxia were also immunoreactive for tyrosine hydroxylase, and were therefore catecholamine cells. Approximately half of the neurons in the nucleus tractus solitarius and two-thirds of neurons in the Kölliker–Fuse nucleus that expressed Fos following moderate hypoxia were retrogradely labelled from the rostral ventrolateral medullary pressor region. Similarly, approximately one quarter of Fos-positive cells in the caudal and intermediate ventrolateral medulla were retrogradely labelled, but very few Fos-positive/retrogradely-labelled cells were found in other pontomedullary or suprapontine brain regions.

The results indicate that systemic hypoxia results in activation of neurons in several discrete nuclei in the brainstem and forebrain, including neurons in all the major pontomedullary catecholamine cell groups. However, neurons that are activated by systemic hypoxia and that also project to the rostral ventrolateral medullary pressor region are virtually confined to the lower brainstem, primarily in the nucleus tractus solitarius and Kölliker–Fuse nucleus and to a lesser extent the caudal/intermediate ventrolateral medulla. In a previous study from our laboratory, we determined the distribution of neurons in the brainstem that are activated by hypertension and that also project to the rostral ventrolateral medullary pressor region [Polson et al. (1995) Neuroscience 67, 107–123]. Comparison of the present results with those from this previous study indicates that the hypoxia-activated neurons in the nucleus tractus solitarius and Kölliker–Fuse nucleus that project to the rostral ventrolateral medulla are likely to be interneurons conveying excitatory chemoreceptor signals, while those in the caudal/intermediate ventrolateral medulla are likely to be mainly interneurons conveying inhibitory baroreceptor signals, activated by the rise in arterial blood pressure associated with the hypoxia-induced hypertension.     

The pressor effect of angiotensin-(1-7) in the rat rostral ventrolateral medulla involves multiple peripheral mechanisms

OBJECTIVE:

In the present study, the peripheral mechanism that mediates the pressor effect of angiotensin-(1-7) in the rostral ventrolateral medulla was investigated.

METHOD:

Angiotensin-(1-7) (25 pmol) was bilaterally microinjected in the rostral ventrolateral medulla near the ventral surface in urethane-anesthetized male Wistar rats that were untreated or treated (intravenously) with effective doses of selective autonomic receptor antagonists (atenolol, prazosin, methyl-atropine, and hexamethonium) or a vasopressin V₁ receptor antagonist [d(CH₂)₅ -Tyr(Me)–AVP] given alone or in combination.

RESULTS:

Unexpectedly, the pressor response produced by angiotensin-(1-7) (16±2 mmHg, n = 12), which was not associated with significant changes in heart rate, was not significantly altered by peripheral treatment with prazosin, the vasopressin V₁ receptor antagonist, hexamethonium or methyl-atropine. Similar results were obtained in experiments that tested the association of prazosin and atenolol; methyl-atropine and the vasopressin V₁ antagonist or methyl-atropine and prazosin. Peripheral treatment with the combination of prazosin, atenolol and the vasopressin V₁ antagonist abolished the pressor effect of glutamate; however, this treatment produced only a small decrease in the pressor effect of angiotensin-(1-7) at the rostral ventrolateral medulla. The combination of hexamethonium with the vasopressin V₁ receptor antagonist or the combination of prazosin, atenolol, the vasopressin V₁ receptor antagonist and methyl-atropine was effective in blocking the effect of angiotensin-(1-7) at the rostral ventrolateral medulla.

CONCLUSION:

These results indicate that angiotensin-(1-7) triggers a complex pressor response at the rostral ventrolateral medulla that involves an increase in sympathetic tonus, release of vasopressin and possibly the inhibition of a vasodilatory mechanism.     

Cardiovascular effects of agmatine within the rostral ventrolateral medulla are similar to those of clonidine in anesthetized rats

Agmatine was isolated from bovine brain in 1994. It exhibits various functions, as a consequence of which it meets the criteria for an endogenous brain neurotransmitter. However, its physiological action on the cardiovascular system remains unclear. This study was designed to clarify its cardiovascular effects when administered into the rostral ventrolateral medulla (RVLM) in anesthetized and paralyzed rats. Unilateral injection of clonidine (5 nmol) into the RVLM significantly decreased mean arterial pressure (MAP) and heart rate (HR). Unilateral injection of agmatine (5 nmol) produced similar effects to clonidine. The amplitude of the decrease in HR was the same as with clonidine, but the amplitude of the decrease in MAP was less pronounced. The cardiovascular inhibition induced by clonidine (5 nmol) and agmatine was abolished by idazoxan (5 nmol). Similar to clonidine, agmatine inhibited the pressor effect of l-glutamate (2 nmol) injected into the RVLM. The duration of this effect (about 6 min) was shorter than that observed with clonidine (about 12 min). Bilateral injection of agmatine into the RVLM inhibited the depressor response induced by baroreflex activation (electrical stimulation of the aortic nerve), and this effect was similar to, but less pronounced than, that induced by clonidine. Idazoxan (5 nmol) antagonized the cardiovascular effects of clonidine and agmatine within the RVLM. However, it produced a similar effect to clonidine injected into the RVLM. It is concluded that agmatine exerts a similar cardiovascular effect to clonidine, with less potency within the RVLM. Idazoxan might be a partial agonist for imidazoline I₁ receptors.     

Commissural NTS lesions enhance the pressor response to central cholinergic and adrenergic activation

Electrolytic lesions of the commissural nucleus of the solitary tract (commNTS) in rats enhance the pressor response to bilateral carotid occlusion or to intravenous infusion of hypertonic NaCl without changing baroreflex responses. In an opposite direction, commNTS lesions abolish the pressor responses to peripheral chemoreflex activation. These opposite effects of commNTS lesions apparently result from an impairment of sympathetic activation in one case and in a facilitation of vasopressin secretion in the others. In the present study, we investigated the effects of the electrolytic lesions of the commNTS in the pressor responses that depend on sympathetic activation and vasopressin secretion produced by central cholinergic or adrenergic activation with intracerebroventricular (i.c.v.) injections of carbachol or noradrenaline, respectively, in unanesthetized rats. Male Holtzman rats (280–320 g, n = 8–15/group) with acute (1 day) or chronic (21 days) sham or commNTS lesions (1 mA × 10 s) and a stainless steel cannula implanted in the lateral ventricle were used. Acute commNTS lesions increased the pressor response to i.c.v. injection of carbachol (0.5 nmol/1 μ1) (52 ± 2, vs. sham: 37 ± 2 mmHg) or noradrenaline (80 nmol/1 μl) (45 ± 6, vs. sham: 30 ± 3 mmHg), whereas chronic commNTS lesions did not affect the pressor responses to the same treatments. Lesions of the commNTS impaired chemoreflex responses produced by intravenous KCN, without changing baroreflex responses. The results suggest that commNTS-dependent inhibitory signals are involved in the modulation of the pressor responses to central cholinergic and adrenergic activation, probably limiting vasopressin secretion.     

Interleukin-1 receptor antagonist reduces the magnitude of the pressor response to acute stress

The purpose of the present study was to establish the effect of chronic central interleukin-1 receptors blockade and central chronic infusion of interleukin-1 beta (IL-1β) on cardiovascular response to an acute stressor. The experiments were performed on 12–14-week-old, male WKY rats, divided into three experimental groups. Each group was subjected to chronic intracerebroventricular (ICV) infusion of one of the following compounds: saline (control, group C), recombinant rat IL-1 receptor antagonist (IL-ANT group) or interleukin-1 beta (IL-1B group). After 5 days of the ICV infusions mean arterial blood pressure (MABP) and heart rate (HR) were recorded continuously under baseline conditions and after the application of an air jet stressor. The stressor was applied three times with 10-min intervals. There were no significant differences in MABP and HR between groups under baseline conditions and immediately before the application of the three consecutive air jets. After the first stressor the IL-ANT group responded with a significantly lower increase in blood pressure than the control and IL-1B group. After the application of the two following air jets only the trend for an intergroup difference was present. The results of the present study provide further evidence that cytokines play an important role in the regulation of the circulatory system. The most important new finding is that the magnitude of the pressor response to the alarming stress is strongly influenced by IL-1 receptors in the brain.     

Nitric oxide producing neurones in the rat medulla oblongata that project to nucleus tractus solitarii

The production of nitric oxide in neurones of the rat medulla oblongata that project to the nucleus tractus solitarii (NTS) was examined by simultaneous immunohistochemical detection of nitric oxide synthase (NOS) and of cholera toxin B-subunit (CTb), which was injected into the caudal zone of the NTS. Neurones immunoreactive for CTb and neurones immunoreactive for NOS were widely co-distributed and found in almost all the anatomical divisions of the medulla. Dual-labelled cells, containing both CTb and NOS immunoreactivities were more numerous ipsilaterally to the injection sites. They were concentrated principally in the more rostral zone of the NTS, raphé nuclei, dorsal, intermediate and lateral reticular areas, spinal trigeminal and paratrigeminal nuclei and the external cuneate and medial vestibular nuclei. Isolated dual-labelled neurones were also scattered throughout most of the divisions of the reticular formation. These observations indicate that many areas of the medulla that are known to relay somatosensory and viscerosensory inputs contain NOS immunoreactive neurones that project to the NTS, and may, therefore, contribute to the dense NOS-immunoreactive innervation of the NTS. The release of nitric oxide from the axon terminals of these neurones may modulate autonomic responses generated by NTS neurones in relation to peripheral sensory stimuli, and thus ultimately regulate sympathetic and/or parasympathetic outflow.     

Nitric oxide synthase in tissues around failed hip prostheses

Nineteen patients who had undergone hip revision surgery for aseptic loosening of joint prostheses were studied. Tissue samples were harvested at the interface between bone and implant, either at the stem or at the cotyle level. Immunohistochemistry was performed on tissue sections to detect nitric oxide synthase (NOS), the enzyme which enables the synthesis of nitric oxide (NO), a molecule which can activate bone resorption. Quantitative analysis of the positive cells and correlation with the presence of particulate wear debris and radiological data were performed.

The authors observed a trend towards a moderate increase in positive cells due to inducible NOS in tissues containing particulate wear debris, especially of a plastic material. This increase, however, did not achieve statistical significance. On the contrary, there was a statistical correlation between iNOS (inducible NOS) and the severity of osteolysis around the prosthetic implant. Pharmacological control of the biosynthesis of NO may be considered in the prevention or treatment of loosening.     

Nitric oxide synthase immunoreactivity in the human ileocecal region

The nitric oxide (NO) producing neurons in the human ileocecal region (pre-junctional ileum, ileocecal and cecocolonic junctions, cecum and post-junctional colon) have been evaluated by immunocytochemistry. The percentage of NO synthase-positive neurons was higher at the myenteric plexus than at the submucous plexus, independently of the levels examined. The inner portion of the circular muscle layer, except at the ileal level, was devoid of immunoreactive nerve fibers. Data obtained suggest that neuronalreleased NO at the ileocecal region has a greater role in the relaxation of the muscle coat, except for the inner circular muscle layer, than in the regulation of blood flow, absorptive and secretory processes.     

慢性乙型肝炎患者体内一氧化氮和一氧化氮合酶水平的研究

目的　探讨慢性乙型肝炎(慢乙肝)患者体内一氧化氮(NO)和一氧化氮合酶(NOS)水平及其意义。方法　检测37例慢乙肝患者NO、NOS[诱生型NOS(iNOS)和结构型NOS(cNOS) ]、肝功能、乙型肝炎病毒(HBV)DNA和HBV基因型(GT)并做出统计分析。结果　慢乙肝患者组与正常对照组比较,NO和iNOS的浓度均明显升高(P <0 0 5 ) ;丙氨酸转氨酶(ALT)异常组与正常对照组及ALT正常组比较:NO和iNOS的浓度均明显升高(P <0 0 5 ) ;ALT正常组与正常对照组比较:NO的浓度明显升高(P <0 0 5 ) ;cNOS在各组间比较差异无统计学意义。在慢乙肝患者中:NO和iNOS浓度与ALT水平呈明显正相关(r=0 36 7,r=0 4 74 )。NO和NOS与HBVDNA指标间均无明显相关关系。不同基因型组之间,NO和NOS的浓度差异无统计学意义(P >0 0 5 )。结论　在慢乙肝患者中,存在NO和iNOS水平升高的现象。慢乙肝患者ALT升高时,NO浓度高,对机体损伤重;慢乙肝患者ALT正常者,NO对机体无明显的损伤。NO和NOS与HBVDNA是相对独立的检测指标。NO水平与不同HBVGT患者病情及预后不同无明显关系。