EFFECTS OF NG-NITRO-l-ARGININE ON PRESSURE NATRIURESIS IN ANAESTHETIZED RABBITS

1. We tested the effects of blockade of nitric oxide synthesis on renal function under conditions of controlled renal artery pressure. Our hypothesis was that endogenous nitric oxide plays a role in the natriuresis that accompanies increased renal perfusion pressure. We used a novel technique which employed an extracorporeal circuit to produce step changes over a wide range of renal artery pressures in pentobarbitone-anaesthetized rabbits. 2. Rabbits were treated with either N^G-itro-l-arginine (NOLA, 20 mg/kg, i.v.; n = 8) or its vehicle (n= 8). Renal artery pressure was set (by adjusting the extracorporeal circuit) at 65, 80, 95, 110 and then 130mmHg respectively, at the beginning of each of five 30 min experimental periods. 3. NOLA treatment caused profound renal vasoconstriction that was largely independent of the level of renal artery pressure, renal blood flow being 35–43% lower in NOLA-treated than in vehicle-treated rabbits across the range of renal artery pressures tested (P= 0.002). NOLA treatment increased filtration fraction (P = 0.02), and tended to reduce glomerular filtration rate (P= 0.09). 4. NOLA-treatment affected sodium excretion in a manner dependent on the level of renal artery pressure, with the slope of the relationship between sodium excretion and renal artery pressure being lower in NOLA-treated than in vehicle-treated rabbits (P= 0.006). 5. These data provide direct evidence that in anaesthetized rabbits endogenous nitric oxide (i) tonically dilates the renal vasculature across a wide range of renal perfusion pressures, and (ii) enhances sodium excretion to a progressively greater degree as renal artery pressure is increased. It may therefore play a role in pressure-induced natriuresis.     

EFFECTS OF DIET ON MEASUREMENT OF NITRIC OXIDE METABOLITES

1. The present study investigated whether a low nitrate/nitrite diet could minimize variability in the measurement of endogenous plasma and urine nitric oxide (NO) metabolites, nitrate and nitrite (NO_x) in normal subjects. 2. Nitrate and nitrite concentrations were measured in plasma and urine as indicators of NO production in six subjects during a free diet and then during a low nitrate/nitrite diet for 6 days. 3. The plasma concentration and 24 h urine NO_x/creatinine ratio were significantly lower on the low nitrate/nitrite diet than on the free diet (P < 0.01). Nitric oxide production appeared to vary greatly within and between subjects, but these variations were substantially decreased by the fourth day of a low nitrate/ nitrite diet. 4. Human plasma and urine NO_x measurements should be determined after a low nitrate/nitrite diet for at least 4 days.     

ACTIONS OF NITRIC OXIDE ON RENAL EPITHELIAL TRANSPORT

1. In vivo studies have demonstrated that nitric oxide (NO) induces natriuresis. Nitric oxide-induced natriuresis occurs independently of changes in renal perfusion pressure, indicating that it is the result of a tubular effect of NO. 2. In support of this hypothesis investigators have shown that NO inhibits both Na⁺-H⁺ exchange and Na⁺/K⁺-ATPase activity in the proximal tubule. In the collecting duct, NO has been shown to decrease sodium flux with no effect on Na⁺/K⁺-ATPase activity. 3. Thus, direct examination of the actions of NO have shown that NO can inhibit sodium transport in the nephron, which may account for the natriuresis observed in vivo.     

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.     

NITRIC OXIDE, THE KIDNEY AND HYPERTENSION

1. According to the renal body fluid feedback mechanism for long-term control, persistent hypertension can only occur as a result of a reduction in renal sodium excretory function or a hypertensive shift in the pressure natriuresis relationship. Although an abnormal relationship between renal perfusion pressure and renal sodium excretion has been identified in every type of hypertension where it has been sought, factors responsible for this effect are still unclear. 2. Nitric oxide (NO) is produced within the kidney and plays an important role in the control of many intrarenal processes that regulate the renal response to changes in perfusion pressure and, thus, help determine systemic vascular volume and blood pressure. Numerous studies have shown that long-term inhibition of NO synthesis results in a chronic hypertensive shift in renal pressure natriuresis. 3. Recent studies have shown that certain animal models of genetic hypertension and forms of human hypertension areas are associated with a decrease in NO synthesis. Reductions in NO synthesis reduce renal sodium excretory function, not only through direct actions on the renal vasculature, but through modulation of other vasoconstrictor processes and through direct and indirect alterations in tubular sodium transport. 4. The causes and consequences of the disregulation of NO in hypertension and other renal disease processes remain an important area of investigation.     

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.     

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.     

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.     

THE NITRIC OXIDE SYSTEM AND CORTISOL-INDUCED HYPERTENSION IN HUMANS

1. The aim of the present study was to assess the role of the nitric oxide (NO) system in cortisol-induced hypertension in humans. 2. Plasma and urinary nitrate/nitrite concentrations and plasma concentrations of arginine and symmetric (SDMA) and asymmetric (ADMA) dimethyl arginine were measured in six subjects on a restricted nitrate diet who were treated with 80 mg/day Cortisol and in subjects on an unrestricted nitrate diet who were treated with Cortisol (80 mg/day, n= 6, or 200 mg/day, n= 10) for 5 days. 3. Cortisol significantly increased systolic and mean arterial pressure. Significant reductions in plasma nitrate/nitrite concentrations were observed in subjects on a restricted nitrate diet on days 3, 4 and 5 of Cortisol treatment (to 11±1, 10±1, 11± pmol/L, respectively) compared with pretreatment (16±1 pmol/L; P<0.01).There were no significant changes in plasma arginine, ADMA or SDMA concentrations. 4. Cortisol treatment significantly increased blood pressure and reduced plasma nitrate/nitrite concentrations. Reductions in plasma nitrate concentrations are not explained by changes in substrate availability or in endogenous nitric oxide synthase inhibitors. These data support a role for the NO system in cortisol-induced hypertension in humans.     

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.     

ENDOTOXIN ALTERS THE SYSTEMIC DISPOSITION OF NITRIC OXIDE SYNTHASE INHIBITORS IN THE AWAKE SHEEP

1. We evaluated the haemodynamic effects and systemic disposition of the nitric oxide synthase (NOS) inhibitor N^L-nitro-L-arginine (NOLA) after intravenous (i.v.) administration of two different doses (5 and 20 mg/kg) in awake healthy sheep and awake sheep given a continuous i.v. infusion of endotoxin (lipopolysaccharide, 12 ng/kg per h, i.v., for 18 h). In addition, we determined the systemic disposition of another NOS inhibitor, N^L-nitro-L-arginine methylester (L-NAME; 20 mg/kg, i.v.) in awake healthy sheep only. 2. A^rL-Nitro-L-arginine produced a dose-dependent decrease in heart rate (HR) and cardiac output (CO) together with a dose-dependent increase in mean arterial pressure (MAP) and peripheral vascular resistance (PVR) when compared to baseline. In endotoxic sheep NOLA produced a greater increase in MAP and mean pulmonary arterial pressure (MPAP). 3. In healthy sheep there was a dose-related increase in total body clearance (CI) of NOLA. The CI increased from 0.028 L/min after the lower dose to 0.032 L/min after the higher dose. The infusion of endotoxin caused an increase in CI of NOLA to 0.040 and 0.047 L/min, respectively, and a decrease in plasma slow half-life (t_1/2 from 825 to 546 min and from 780 to 453 min, respectively. 4. N^L-Nitro-L-arginine methylester was rapidly cleared from the plasma with a slow half-life of approximately 7.5 min and there was a simultaneous appearance of NOLA in the plasma. 5. These results support the view that nitric oxide has a significant role in regulating vascular tone in healthy and endotoxic sheep and indicate that the increases in CI of NOLA with an increase in its dose and the presence of endotoxin will be important in influencing appropriate dosage regimens in clinical studies.     

INHIBITION OF ENDOTHELIAL NITRIC OXIDE BIOSYNTHESIS BY N-NITRO-l-ARGININE

1. The actions of N-nitro-L-arginine (NOLA) on the release of nitric oxide (NO) from arterial endothelial cells was studied in rat isolated thoracic aortic rings and by bioassay of NO derived from cultured bovine aortic endothelial cells. 2. NOLA (3-10 mumol/L) caused concentration-dependent inhibition of acetylcholine-induced relaxation of phenylephrine-contracted rat aortic rings, which is dependent on the release of NO from the endothelium. The inhibitory actions of NOLA could be prevented by pre- and co-incubation with L-arginine (1 mmol/L). 3. Endothelium-independent relaxation induced by sodium nitroprusside was not affected by NOLA. 4. The release of NO from bovine aortic endothelial cells, induced by bradykinin (10 nmol/L), was detected by bioassay on pre-contracted rabbit aortic strips. NOLA (1-3 mumol/L, given through the cell column) reduced or abolished the release of NO, but did not affect relaxations of the bioassay tissues induced by glyceryl trinitrate or authentic NO. 5. These data indicate that NOLA potently inhibits the biosynthesis of NO from L-arginine, and thus prevents its release from arterial endothelial cells. It may be a useful pharmacological tool for probing the significance of NO biosynthesis in cardiovascular function.     

NITRIC OXIDE INHIBITION DOES NOT PREVENT THE HYPOTENSIVE RESPONSE TO INCREASED RENAL PERFUSION IN RABBITS

1. The involvement of nitric oxide (NO) and platelet activating factor (PAF) in the systemic depressor responses to increased renal perfusion pressure (RPP) were investigated. 2. In anaesthetized rabbits, the left kidney was perfused via an extracorporeal circuit which allowed RPP to be increased from 65 mmHg to 125 mmHg. The response of systemic blood pressure (SBP) to increasing RPP was measured in the same rabbits. 3. One group of rabbits (n = 5) was treated with N^G-nitro-L-arginine (NOLA) to inhibit NO synthase activity (20 mg/kg i.v. bolus). Another group (n= 5), received 250mmol/L NaHCO₃ (4mL/kg bolus) as vehicle treatment. 4. Following an increase in RPP to 125 mmHg, SBP fell at a rate of 0.43 ± 0.06 mmHg/min in the vehicle treated rabbits. After NO synthase inhibition the rate of fall in SBP of 0.34 ± 0.07 mmHg/min was not significantly different from that in the vehicle group (P= 0.3). 5. Blockade of NO synthesis did not alter the renal blood flow, renal vascular resistance changes and pressure-related natriuresis and diuresis responses to increased RPP to 125 mmHg. 6. PAF receptor blockade, using WEB 2086 (0.5 mg/kg plus 0.5 mg/kg/h), did not alter the systemic, renal haemodynamic or urinary responses to increasing renal perfusion pressure to 125 mmHg. 7. These findings indicate that neither NO nor PAF play an important role in the blood pressure lowering activity, intrarenal haemodynamics and urinary excretory responses observed when RPP was increased to a level within the physiological range.     

ENDOGENOUS NITRIC OXIDE PRODUCTION IS AUGMENTED AS THE SEVERITY ADVANCES IN PATIENTS WITH LIVER CIRRHOSIS

• 1 Since endothelium-derived nitric oxide (NO) is a potent vasodilator and degraded into nitrous ions, we measured the serum nitrate ion (NO₃^?) and the amount of urinary excretions of NO₃^? as an index for endogenous NO to ascertain whether NO formation is augmented in patients with chronic liver diseases.
• 2 Using inpatients suffering from chronic liver diseases, serum levels and urinary excretions of NO₃^? were measured by using high-performance liquid chromatography with an anion exchange column.
• 3 Among the four patient groups of normal controls, and those with chronic liver diseases such as chronic active hepatitis, compensated cirrhosis, and decompensated cirrhosis the serum level of NO₃^? showed the highest level in a patient group with decompensated cirrhosis. The amount of urinary excretion of NO₃^? was significantly increased in both groups of patients with liver cirrhosis compared with the control group and patients with chronic active hepatitis. Patients with chronic active hepatitis did not show any difference between the normal control group. The amount of urinary excretion of NO₃^? correlated significantly and negatively with the level of serum albumin (P<0.05) and counts of platelets (P< 0.01) in patients with compensated cirrhosis.
• 4 These findings suggest that the production of endogenous NO is augmented in patients with liver cirrhosis, particularly in a decompensated subgroup. Increases in the production of endogenous NO correspond to the progress of liver cirrhosis, but not in patients with chronic hepatitis.

     

武汉地区海洛因依赖者血清中一氧化氮分析

探讨近年来新发现的生物信息递质一氧化氮 (NO)与海洛因依赖的关系。方法··:将87例海洛因依赖者分别按不同年龄分为4组 ,按不同吸毒年限分为3组 ,按不同吸毒途径分为2组 ,用半自动生化分析仪检测其血清NO水平 ,比较组间及其与对照组 (健康体检者 )的差异程度。结果··:不同年龄组海洛因依赖者的血清NO水平显著高于对照组 (P<0.001)。在不同吸毒年限中 ,NO水平与吸毒年限呈正相关 ,且A组 (2a以下 )与B组 (2-5a) ,B组与C组 (5a以上 )比较差异有统计学意义 ,(P<0.05)。A组与C组比较差异有显著意义 (P<0.01)。不同吸毒途径的两组间比较,静脉注射海洛因依赖者的血清NO水平显著升高 (P<0.001)。结论··:NO参与海洛因依赖过程 ,并与吸毒年限、吸毒途径有密切关系。     

MODULATION OF VASOCONSTRICTION BY ENDOTHELIUM-DERIVED NITRIC OXIDE: THE INFLUENCE OF VASCULAR DISEASE

1. The endothelium makes a significant contribution to the regulation of vascular tone through the release of potent vasodilator agents such as nitric oxide (NO) and prostacyclin (PGI₂) as well as vasoconstrictor compounds such as endothelin. Recognition of this function of the endothelium has created a new focus for the investigation of vasoconstrictor activity under physiological and pathological conditions. 2. It has been well established that removal of the endothelium enhances responses to a variety of contractile agents in conductance arteries and that such modulation is predominantly due to the release of NO. The use of selective inhibitors of NO synthesis has confirmed that the endothelium-derived nitric oxide also modulates constriction in resistance vessels. 3. In a number of cardiovascular disease states there is impairment of endothelial function. Thus one of the consequences of atherosclerosis, hypertension and ischaemia is a reduction in endothelium-dependent vasodilatation, both at a basal level and in response to endogenous and exogenous stimuli. In addition, enhanced responses to vasoconstrictors have been reported in those disease states. Such observations have led to the attractive hypothesis that enhanced constriction in vascular disease results from attenuate NO-induced dilatation. However, whilst there is some evidence that pathological impairment of endothelial function is accompanied by increased constrictor activity, particularly where serotonergic mechanisms are involved, it is inappropriate to make the general assumption that where disease impairs NO activity there will also be increased sensitivity to all constrictor stimuli.     

NITRIC OXIDE: ROLE IN NEUROTOXICITY

1. Nitric oxide (NO) is a novel neuronal messenger molecule which interacts with surrounding neurones, not by synaptic transmission but by diffusion between cells. 2. No is produced following stimulation of the enzyme, NO synthase (NOS). After synthesis, NO exerts its biological actions by diffusion to the site of action. Therefore, the way to regulate the physiological actions of NO is to regulate NOS. 3. NOS is activated by the influx of calcium from glutamate-activated N-methyl-D-aspartate receptors. Overactivation of these receptors leads to overproduction of NO and neuronal cell death. 4. NOS can be regulated at the catalytic site, at the flavoproteins, at the calmodulin site and by phosphorylation. 5. In excess, NO is toxic to neurones. This toxicity is mediated largely by an interaction with the superoxide anion, presumably through the generation of the oxidant, peroxynitrite. 6. NO or peroxynitrite-mediated neuronal injury involves the activation of the nuclear protein, poly(ADP-ribose)synthetase.