褪黑素对大脑皮层细胞一氧化氮含量及其神经毒性作用的影响

目的：探讨褪黑素(MT)抗衰老作用与神经细胞NO释放之间的联系。方法：连续给予老年小鼠MT，检测大脑皮层神经细胞NO含量的变化,并用原代培养的大鼠皮层神经元，去血清培养后，观察MT对高钾、谷氨酸（Glu）诱发NO释放及硝普钠（SNP）致神经毒性作用的影响。结果：MT能明显抑制老年小鼠脑内NO含量的增高，并拮抗KCI与Glu诱发的NO释放及SNP引起的神经毒性，对大脑神经元有保护作用。结论：MT抑制大脑皮层NO含量增高，可能是其抗衰老作用的机制之一。     

ROLE OF NITRIC OXIDE IN THE DEVELOPMENT OF CORTICOTROPIN-INDUCED HYPERTENSION IN SHEEP

1. The possibility that altered synthesis of vascular nitric oxide (NO) plays a role in the development of corticotropin-induced hypertension in sheep was examined by determining the effect of concomitant infusion of L-arginine, a precursor of NO, on the development of the hypertension. 2. Corticotropin (5 μg/kg per h) infused over 2 days increased mean arterial pressure (MAP) from 83 ± 4 to 99 ± 4 mmHg in five conscious sheep. Concomitant infusion of L-arginine (60 mg/kg per h) did not alter this response; infusion of L-arginine alone had no effect on blood pressure. 3. The dose of L-arginine (60 mg/kg per h) used blocked the rise in MAP (+16 mmHg) in response to a 5 h infusion of N-nitro-L-arginine (1 mg/kg per h). 4. These findings suggest that disruption of NO synthesis does not play a role in the development of corticotropin hypertension in sheep.     

ROLE OF NITRIC OXIDE IN THE CONTROL OF THE RENAL MEDULLARY CIRCULATION

1. Nitric oxide (NO) has been implicated as an important controller in the short- and long-term regulation of arterial pressure. Studies performed in our laboratory have demonstrated that chronic intravenous administration of the NO synthase inhibitor N^G-nitro-L-arginine methyl ester (L-NAME) selectively decreases renal medullary blood flow, causes sodium and water retention and leads to hypertension. 2. To determine the importance of the renal medullary effects in this model of hypertension, further studies were conducted to examine the influence of selective stimulation or inhibition of renal medullary NO on whole kidney function and cardiovascular homeostasis. With the use of a unique catheter to directly infuse into the renal medullary interstitial space, stimulation (bradykinin or acetylcholine) or inhibition (L-NAME) of renal medullary NO selectively increased or decreased renal medullary blood flow. 3. The changes in medullary flow in these experiments were associated with parallel changes in sodium and water excretion independent of alterations in renal cortical blood flow or glomerular filtration rate. 4. Studies were then undertaken to examine the long-term effects of selective NO inhibition in the renal medulla on cardiovascular homeostasis. Chronic infusion of L-NAME directly into the renal medullary interstitial space of uninephrectomized Sprague-Dawley rats led to a selective decrease in renal medullary blood flow that was sustained throughout the 5 day L-NAME infusion period. The decrease in medullary blood flow was associated with retention of sodium and the development of hypertension and the effects were reversible. 5. The data reviewed indicate that NO in the renal medulla has a powerful influence on fluid and electrolyte homeostasis and the control of blood pressure.     

ROLE OF NITRIC OXIDE IN TUBULOGLOMERULAR FEEDBACK: EFFECTS OF DIETARY SALT

1. The tubuloglomerular feedback (TGF) response operates primarily by vasoconstriction of the afferent arteriole and a fall in glomerular capillary pressure (P_GC) and single-nephron glomerular nitration rate (SNGFR) during increased NaCl reabsorption in the macula densa (MD). Numerous studies have suggested that nitric oxide (NO) is synthesized by the MD and acts to suppress TGF. As a high-salt (HS) diet has been found to blunt TGF, we tested the effects of salt intake on NO-dependent changes in TGF. 2. In the first series of experiments, values of SNGFR were contrasted from samples of tubular fluid taken from the proximal tubule (PT; MD delivery interrupted) and the distal tubule (DT; MD delivery intact). Compared with HS rats, the difference between PT and DT values of SNGFR was increased in low-salt (LS) diet rats (4.3 ± 0.4 vs 10.3 ± 1.2 nL/min, respectively; P < 0.001). Intravenous infusion of iV^G-monomethyl-L-arginine (L-NMMA), in pressor doses increased the difference between PT and DT values of SNGFR of HS rats (4.3 ± 0.4 vs 9.5 ± 1.2 nL/min before and during L-NMMA, respectively; P < 0.001) without significantly affecting values in LS rats (10.3 ± 1.2 vs 12.3 ± 1.4 nL/min before and during L-NMMA, respectively; NS). 3. A second series of experiments assessed TGF responses directly. Changes in stop-flow pressure (PSF; an index of P_GC) were measured in response to graded perfusion of the loop of Henle (LH) with artificial tubular fluid. Loop perfusion with 10_-3 mol/1. L-NMMA did not affect the PSF responses of LS rats but did reduce (P < 0.01) the PSF of HS rats during perfusion at 20 nL/min (-1.5±0.4mmHg; P<0.01), 30nL/min (-1.8 ± O.5 mmHg; P < 0.01) and 40 nL/min (-2.2 ± 0.5 mmHg; P < 0.001). 4. We conclude that the TGF response is increased by suppression of NOS activity during HS but not LS intake.     

ROLE OF l-ARGININE IN NITRIC OXIDE PRODUCTION IN HEALTH AND HYPERTENSION

• 1 l ‐Arginine is the substrate for vascular nitric oxide (NO) formation. Under normal physiological conditions, intracellular l ‐arginine levels far exceed the K_m of NO synthase for l ‐arginine. However, endogenous NO formation is dependent on extracellular l ‐arginine concentrations, giving rise to the concept of the ‘l ‐arginine paradox’.
• 2 Nitric oxide production in epithelial and endothelial cells is closely coupled to cellular l ‐arginine uptake, indicating that l ‐arginine transport mechanisms play a major role in the regulation of NO‐dependent function.
• 3 Consistent with the data in endothelial and epithelial cells are functional data indicating that exogenous l ‐arginine can increase renal vascular and tubular NO bioavailability and thereby influence kidney perfusion, function and arterial pressure. The integrated effect of increased cellular l ‐arginine transport is to lower arterial pressure. Therefore, the use of l ‐arginine in the treatment of hypertension warrants investigation.
• 4 Low NO bioavailability is central to the development and maintenance of hypertension and to related endothelial dysfunction and target organ damage. We propose that l ‐arginine can interrupt the vicious cycle that initiates and maintains low NO in hypertension by increasing the formation of NO.

     

EVIDENCE FOR A ROLE OF NITRIC OXIDE IN THE NEUROTRANSMITTER SYSTEM MEDIATING RELAXATION OF THE RAT ANOCOCCYGEUS MUSCLEC

1. The nitric oxide (NO) synthesis inhibitor NG-monomethyl-L-arginine (L-NMMA), but not D-NMMA, inhibited the NANC-mediated relaxations of the rat anococcygeus muscle, but did not affect the relaxation produced by sodium nitroprusside. 2. The inhibitory effect of L-NMMA was reversed by L-arginine but not by D-arginine, and prior exposure to L-arginine blocked the effect of L-NMMA. 3. The noradrenergically mediated contractions of the anococcygeus elicited by field stimulation were slightly enhanced by L-NMMA, but the response to noradrenaline was not affected. 4. The results suggest that NANC transmission in the rat anococcygeus muscle involves the generation of NO from arginine.     

17β-OESTRADIOL ENHANCES NITRIC OXIDE SYNTHASE ACTIVITY IN ENDOTHELIUM-DENUDED RAT AORTA

1. It has been suggested that oestrogen-produced vasodilatation is due to induction of endothelial nitric oxide synthase (NOS), but there are many reports of direct effects on vascular smooth muscle. In the present study, these processes were investigated in rat aorta isolated from ovariectomized rats. 2. Short-term treatment (10min) with 17β-oestradiol (10 μmol/L) produced a small attenuation of the phenylephrine (PE)-induced constriction, which was unaffected by the nitric oxide synthase inhibitor l-N 5(-1-iminoethyl)ornithine (NIO; 100μmol/L). Long-term treatment (6h) with 17β-oestradiol (10 μmol/L) did not affect acetylcholine-mediated vasorelaxation in endothelium-intact aortic rings, but did attenuate PE-induced constriction. This attenuation was also observed in endotheliumdenuded preparations after 17β-oestradiol (10 μmol/L for 6h) and was far greater than the acute effect of 17β-oestradiol (10 μmol/L). 3. The attenuation produced by 17β-oestradiol (10 μmol/L for 6 h) was significantly inhibited by concomitant treatment with cycloheximide (1 μmol/L), suggesting that protein synthesis was involved. NIO (100 μmol/L) also attenuated the effect, which suggests that the anti-constrictor effect of 17β-oestradiol occurs through the increased production of nitric oxide (NO). 17β-Oestradiol increased NO production, as assessed by the conversion of [³H]-arginine to [³H]-citrulline in rat aorta. These effects were prevented by cycloheximide and NIO. The anti-constrictor effect of oestrogen was blocked by the oestrogen receptor antagonist ICI 182780 (100nmol/L). 4. Western blotting using an antibody specific for inducible nitric oxide synthase (NOS) revealed that 17β-oestradiol (10 μmol/L for 24 h) treatment induced the formation of inducible NOS protein in the aorta, an effect blocked by cycloheximide. The results indicate that 17β-oestradiol can attenuate the vasoconstrictor effect of PE by a specific receptor-mediated process that involves induction of inducible NOS.     

AUGMENTED ENDOGENOUS NITRIC OXIDE PRODUCTION IN PARTIAL PORTAL VEIN-LIGATED RATS

1. Endothelium-derived nitric oxide (NO) is a potent vasodilator. Because the body oxidizes it to nitrate ions, NO₃-, measurement of the serum concentration and the urinary excretion of NO₃- may be an index for endogenous NO. We investigated the role of NO on hyperdynamic circulation in cirrhotic and partial portal vein-ligated rats by measuring NO₃. 2. Liver cirrhosis was induced by administration of thioacetamide. Systemic and splanchnic haemodynamics and splenic-systemic shunting were determined by tracer microspheres. The concentration of NO₃- was measured by using high-performance liquid chromatography with an anion-column. 3. We found that systemic and splanchnic hyperdynamic circulation existed to almost the same extent in cirrhotic and in portal vein-ligated rats as compared to the controls and sham-operated rats, respectively. Splenic-systemic shunting was markedly greater in portal vein-ligated rats than in cirrhotic rats. 4. Serum NO₃- levels and urinary excretion of NO₃- in cirrhotic rats tended to increase as compared to the controls. On the other hand, the levels in portal vein-ligated rats were significantly increased as compared to those of the sham-operated rats, and were significantly and negatively correlated to the splanchnic arterial resistance and total vascular resistance. The amount of urinary excretion of NO₃- significantly correlated to splenic-systemic shunting (r = 0.61, P<0.05) only in portal vein-ligated rats. 5. We suggest that these high levels of NO₃- in portal vein-ligated rats relate to the extensive formation of porto-collateral vasculature or acute changes in systemic and splanchnic haemodynamics due to portal vein-ligation.     

NITRIC OXIDE IN THE MEDIATION OF PRESSURE NATRIURESIS

1. Recent studies have indicated that nitric oxide (NO) production in the kidney contributes to the regulation of renal haemodynamics and excretory function. Inhibition of nitric oxide synthase (NOS) reduces renal blood flow by approximately 25% and markedly reduces sodium excretion without reductions in filtered load. In particular, inhibition of NO synthesis markedly suppresses the slope of the arterial pressure-mediated response in sodium excretion. 2. Further studies have shown that constant intrarenal infusion of a NO donor in dogs treated with a NOS inhibitor produced diuretic and natriuretic responses but failed to restore the slope of the pressure-induced natriuretic response. These data indicate that an alteration in intrarenal NO activity, rather than the simple presence of NO during changes in arterial pressure is required for full expression of pressure natriuretic responses. 3. In support of the hypothesis that NO is involved in the mediation of pressure natriuresis, we also recently demonstrated a direct relationship between changes in arterial pressure and urinary excretion rate of sodium as well as nitrate and nitrite (a marker for endogenous NO activity) in the presence of efficient autoregulation of cortical and medullary blood flow. 4. The direct inhibitory actions of NO on tubular sodium reabsorption have also been observed in cultured tubular cells as well as isolated, perfused cortical collecting duct segments. 5. Thus, the collective data suggest that acute changes in arterial pressure induce changes in intrarenal NO production, which may directly alter tubular reabsorptive function to manifest the phenomenon of pressure natriuresis.     

RENAL VASOCONSTRICTION IS MODULATED BY NITRIC OXIDE

1. The effect of the nitric oxide synthesis inhibitor, NG-nitro-L-arginine (NOLA), has been examined on vascular reactivity in the rat isolated perfused kidney. 2. NOLA (10 mumol/L) had no effect on basal perfusion pressure, but significantly enhanced the vasoconstrictor responses to sympathetic nerve stimulation (1-16 Hz, 10 s) and noradrenaline (10-300 pmol). The enhancements were greater with the lower frequencies of stimulation and lower doses of noradrenaline. 3. The enhancing effect of 10 mumol/L NOLA on vasoconstrictor responses to nerve stimulation was partially prevented by 100 mumol/L L-arginine while 100 mumol/L D-arginine had no effect. 4. The results suggest that nitric oxide attenuates vasoconstrictor responses in the rat kidney, and provide evidence that nitric oxide has a physiological role in the modulation of vascular reactivity.     

VALIDATION AND IN VITRO NEUROTOXICITY

1. Validation of in vitro systems for studying neurotoxicants generally has not been accomplished, although in vitro tests have been used as screens to identify potential neurotoxic hazards and to study mechanisms. 2. A number of factors need to be taken into account when a test is validated: (i) a rationale for developing the test; (ii) clear biological or pathophysiological relevance of the endpoint to the effect detected in vivo; (iii) a standardized protocol and evidence of intra- and interlaboratory reproducibility; (iv) testing of chemicals representative of the categories of interest, including very toxic, moderately toxic and relatively non-toxic substances; and (v) a method to statistically evaluate the data. 3. Proper validation should lead to methods which can be used by regulatory agencies to make decisions regarding hazard/risk.     

吗啡依赖大鼠脊髓和脑干一氧化氮含量和合酶活力分析

本文检测了吗啡依赖大鼠脊髓和脑干一氧化氮合酶（ＮＯｓ）活力,一氧化氮（ＮＯ）以及ｃＧＭＰ含量。结果显示吗啡依赖大鼠脊髓ＮＯｓ活力,ＮＯ和ｃＧＭＰ含量较正常对照组降低,脑干中ＮＯｓ活力轻度降低,而ＮＯ和ｃＧＭＰ含量降低。纳洛酮激发戒断症状后大鼠脊髓和脑干ＮＯｓ活力,ＮＯ以及ｃＧＭＰ含量急剧升高。ＮＯｓ抑制剂Ｌ－Ｎ－硝基精氨酸甲酯（Ｌ－ＮＡＭＥ）处理可以抑制大鼠吗啡戒断反应,同时减少脊髓和脑干ＮＯ含量。结果表明吗啡戒断反应与脊髓和脑干的ＮＯ－ｃＧＭＰ途径的兴奋有关。     

吗啡依赖大鼠脊髓和脑干一氧化氮含量和合酶活力分析

本文检测了吗啡依赖大鼠脊髓和脑干一氧化氮合酶（ＮＯｓ）活力,一氧化氮（ＮＯ）以及ｃＧＭＰ含量。结果显示吗啡依赖大鼠脊髓ＮＯｓ活力,ＮＯ和ｃＧＭＰ含量较正常对照组降低,脑干中ＮＯｓ活力轻度降低,而ＮＯ和ｃＧＭＰ含量降低。纳洛酮激发戒断症状后大鼠脊髓和脑干ＮＯｓ活力,ＮＯ以及ｃＧＭＰ含量急剧升高。ＮＯｓ抑制剂Ｌ－Ｎ－硝基精氨酸甲酯（Ｌ－ＮＡＭＥ）处理可以抑制大鼠吗啡戒断反应,同时减少脊髓和脑干ＮＯ含量。结果表明吗啡戒断反应与脊髓和脑干的ＮＯ－ｃＧＭＰ途径的兴奋有关。     

EFFECT OF HOMOCYSTEINE ON THE PRODUCTION OF NITRIC OXIDE IN ENDOTHELIAL CELLS

1. Homocysteine decreased the release of nitric oxide in cultured human umbilical vein endothelial cells. 2. Homocysteine did not affect constitutive and inducible nitric oxide synthase activity.     

ROLE OF NITRIC OXIDE IN THE CONTROL OF GLOMERULAR MICROCIRCULATINO

1. Nitric oxide (NO) plays an important role in the control of glomerular haemodynamics and is synthesized from the amino acid L-arginine by a family of enzymes, NO synthase (NOS). 2. Nitric oxide synthase is present in the endothelium and also in the macula densa, a plaque of specialized tubular epithelial cells. Endothelial NOS is known to be stimulated by shear stress and hormones, while the factor that regulates the activity of macula densa NOS remains undefined. 3. Studies with the in vitro microperfusion of glomerular arterioles have shown that the constriction of afferent arterioles (Af-Art) induced by myogenic responses and angiotensin II (AngII) is stronger in the absence rather than in the presence of luminal flow. Furthermore, endothelial disruption or NOS inhibition abolishes such differences, suggesting that flow through the lumen stimulates the endothelium to synthesize and release NO, which in turn attenuates both the myogenic response and the action of AngII in the Af-Art. 4. In contrast, NOS inhibitors have no effect on efferent arteriolar (Ef-Art) constriction induced by AngII. 5. In preparations in which Af-Art and the macula densa are simultaneously microperfused, selective inhibition of macula densa NOS has been shown to augment Af-Art constriction when the NaCl concentration at the macula densa is high, suggesting that the macula densa produces NO, which in turn modulates tubuloglomerular feedback. 6. Thus, the differential actions of NO in the Af-Art, Ef-Art and the macula densa may be important in the control of glomerular haemodynamics under various physiological and pathological conditions.     

RESTORATION OF NITRIC OXIDE FUNCTION IN HUMAN HYPERLIPIDAEMIA, CONGESTIVE HEART FAILURE AND LIVER CIRRHOSIS

1. There is accumulating evidence for a range of abnormalities in the nitric oxide (NO) signalling cascade in human cardiovascular disorders. 2. In the present review we assess the literature detailing such evidence in early (hyperlipidaemia) and end-stage (heart failure) disease, with emphasis on the mechanisms by which the disturbances are thought to occur. 3. Strategies for the correction of disturbed NO signalling in these states are reviewed and include both prescribed pharmacological interventions, such as lipid-lowering therapy and novel uses of angiotensin-converting enzyme inhibitors, as well as non-pharmacological interventions, such as exercise and dietary supplementation with l -arginine and n-3 polyunsaturated fatty acids. 4. In addition to a decreased production/function of NO, the possible detrimental effects of a chronic elevation in NO production in patients with liver cirrhosis, together with a novel use of antibiotics to correct this perturbation, is outlined.     

INVOLVEMENT OF OXIDATIVE AND L-ARGININE-NO PATHWAYS IN THE NEUROTOXICITY OF DRUGS OF ABUSE IN VITRO

1. Inhibitors of nitric oxide (NO) formation or ADP-ribosylation attenuate methamphetamine (METH)- and methyl-enedioxymetamphetamine (MDMA)-induced neurotoxicity on dopaminergic and serotonergic cells in primary cultures. 2. They also prevent METH-induced reactive gliosis in dopaminergic cultures. 3. Overexpression of superoxide dismutase (SOD) in cells obtained from SOD-transgenic mice also attenuates drug-induced toxicity. 4. These data indicate a role for oxygen-based and NO free radicals in the mechanisms of cell death associated with drugs of abuse in vitro.     

OXYGEN RADICALS AND NITRIC OXIDE IN RAT MESENTERIC ISCHAEMIA-REPERFUSION: MODULATION BY L-ARGININE AND NG-NITRO-L-ARGININE METHYL ESTER

1. The aims of the present study were to detect changes in superoxide anion (O₂^?), nitric oxide (NO) and other reactive oxygen species (ROS) directly by measurement of chemilumin-escence (CL) and to investigate the role of L-arginine, a nitric oxide synthase (NOS) substrate, and N^G-nitro-L -arginine methyl ester (L-NAME), a NOS inhibitor, together with their molecular enantiomers D-arginine and D-NAME, in a rat mesenteric ischaemia-reperfusion (I/R) model. 2. Seventy-nine female Wistar albino rats were divided into eight groups. The first three groups underwent sham operation; group 1 was the control group, group 2 received L-arginine and group 3 received L-NAME. Ischaemia was produced in the remaining five groups by ligation of the superior mesenteric artery for 30 min followed by 60 min reperfusion. Group 4 rats were control I/R rats and groups 5-8 received either L-arginine, L-NAME, D-arginine or D-NAME, respectively. 3. Both luminol and lucigenin CL was significantly increased in I/R groups compared with sham-operated groups. L-Arginine significantly reduced CL measurements. D-Arginine was also protective, but not as much as L-arginine. Both L - and D-arginine had in vitro O₂^?-scavenging potential, as tested by the xanthine-xanthine oxidase system. N^G-Nitro-L-arginine methyl ester decreased lipid peroxidation values in addition to reducing CL measurements. Nitric oxide concentrations were significantly increased in I/R groups in comparison with sham-operated groups. Peroxynitrite formation was increased by I/R. Treatment with L-NAME was beneficial by reducing NO concentrations in the reperfused ileum. 4. In our I/R model, O₂^?, NO and other ROS were increased. Although NOS inhibitors were effective in reducing oxidative damage, increasing NO concentrations with L-arginine was also beneficial, presumably due to the ability of L-arginine to inhibit phagocyte adherence and its radical scavenging potential. In fact, NO may have different effects in terms of tissue injury or protection depending on the concentration of oxygen and the haemodynamic state of the tissue.