L-arginine is the physiological precursor for the formation of nitric oxide in endothelium-dependent relaxation

Effects of L-arginine on lower limb vasodilator reserve and exercise capacity in patients with chronic heart failure

OBJECTIVE

To determine whether the reactive hyperaemic response of the lower limb increases with improved exercise capacity after acute supplementation with L-arginine, the precursor of nitric oxide, in patients with chronic heart failure.

METHODS

19 patients with chronic heart failure were enrolled in the study. Rest calf blood flow and femoral occlusion induced calf blood flow changes were measured by venous occlusion plethysmography before and after intravenous infusion of 10% L-arginine solution (5 ml/kg for 30 minutes) or placebo. Postexercise calf blood flow was also measured after the experimental infusion. During both postinfusion periods, several exercise capacity indices were determined by a symptom limited cardiopulmonary exercise test using a bicycle ergometer.

RESULTS

Baseline calf blood flow, systemic blood pressure, and heart rate showed no significant changes in either of the two experimental conditions. However, the occlusion induced blood flow response was significantly enhanced by L-arginine infusion (mean (SEM) peak flow, 19.6 (1.5) v 28.9 (3.1) ml/min/dl calf tissue; p < 0.01), but not by placebo (peak flow, 19.1 (1.4) v 20.9 (1.8) ml/min/dl calf tissue; NS). Calf blood flow response after exercise was also higher after L-arginine infusion than after placebo (peak flow, 4.8 (0.4) v 6.0 (0.8) ml/min/dl calf tissue; p < 0.05). L-arginine infusion had no significant effect compared with placebo on exercise capacity indices such as peak oxygen uptake (17.1 (1.0) v 15.8 (1.1) ml/min/kg; NS), anaerobic threshold (10.5 (0.6) v 10.4 (0.7) ml/min/kg; NS), and exercise time (296 (23) v 283 (22) s; NS).

CONCLUSIONS

Acute supplementation with the nitric oxide precursor L-arginine increased lower limb reactive hyperaemia but did not lead to any significant improvement in exercise capacity in patients with chronic heart failure.

Pharmacokinetic-pharmacodynamic profile of systemic nitric oxide-synthase inhibition with L-NMMA in humans

AIMS

It has been demonstrated that inhibition of endothelium derived nitric oxide with NG-monomethyl-L-arginine (L-NMMA) results in a different cardiac and peripheral vascular response. The purpose of this study was to investigate the pharmacokinetic-pharmacodynamic profile of L-NMMA and pharmacokinetic interactions with L-arginine in healthy subjects.

METHODS

Plasma pharmacokinetics were analysed from two different studies: In study 1, 3 mg kg-1 L-NMMA was administered i.v. over 5 min and systemic haemodynamics, cardiac output (CO), fundus pulsation amplitude (FPA), and NO-exhalation (exhNO) were measured at baseline and 15, 65, 95, 155, and 305 min after start of drug administration (n=7). In study 2, 17 mg kg-1 min-1 of the physiologic substrate for nitric oxide synthase, L-arginine, was coinfused i.v. over 30 min with a primed constant infusion of 50 microg kg-1 min-1 L-NMMA (n=8).

RESULTS

Bolus infusion of L-NMMA resulted in a maximum plasma concentration of 12. 9+/-3.4 microg ml-1 (mean+/-s.d.) with elimination half-life of 63. 5+/-14.5 min and clearance of 12.2+/-3.5 ml min-1 kg-1 and caused a small hypertensive response, decreased CO by 13%, FPA by 26%, exhNO by 46% and increased systemic vascular resistance by 16% (P<0.05 each) 15 min after start of drug administration. Although only limited data points were available in the L-NMMA plasma concentration range between 0 and 4 microg ml-1, drug effects over time were in good agreement with an Emax model (r2>0.98 each), which also suggested that concentrations producing half-maximum effects were higher for FPA than for CO and exhNO. The coinfusion with L-arginine caused a nearly two-fold increase in plasma L-NMMA levels, indicating a pharmacokinetic interaction.

CONCLUSIONS

In the absence of a systemic hypertensive response, L-NMMA significantly decreased CO, exhNO, and FPA. The concentration calculated to produce a half maximal effect was equivalent for exhNO and CO, but markedly higher for FPA. Furthermore, measurement of FPA is susceptible to changes in L-NMMA levels at small plasma concentrations.

Both extracellular ATP and shear stress regulate the release of nitric oxide in rat caudal artery

1. To elucidate the physiological role of nitric oxide (NO) in regulating vascular tone, the effects of NG-nitro-L-arginine methyl ester (L-NAME), an NO synthase inhibitor, on the vasoconstrictor response to noradrenaline (NA) in rat caudal artery was examined. 2. NG-Nitro-L-arginine methyl ester significantly potentiated the NA-induced increase in perfusion pressure in the perfused caudal artery, but did not affect the NA-induced contraction in caudal artery ring preparations. In addition, an increase in perfusion pressure mechanically produced by a stepwise increase in flow rate was not affected by L-NAME. 3. Noradrenaline evoked a significant increase in the release of endogenous ATP and its metabolites from the perfused artery, whereas increased perfusion pressure as a result of increased flow rate did not evoke release of endogenous ATP. 4. In the presence of exogenously applied ATP, L-NAME significantly potentiated the increase in perfusion pressure produced by increased flow rate. 5. These results indicate that perfused vascular tone is regulated by endogenous NO and suggest that extracellular ATP may participate in the synthesis and release of NO by shear stress in endothelial cells in the rat caudal artery.

Ginsenoside Rg3 mediates endothelium-dependent relaxation in response to ginsenosides in rat aorta: role of K+ channels

The aim of the present study was to characterize the endothelium-dependent relaxation elicited by ginsenosides, a mixture of saponin extracted from Panax ginseng, in isolated rat aorta. Relaxations elicited by ginsenosides were mimicked by ginsenoside Rg1 and ginsenoside Rg1, two major ginsenosides of the protopanaxatriol group. Ginsenoside Rg3 was about 100-fold more potent than ginsenoside Rg1. The endothelium-dependent relaxation in response to ginsenoside Rg3 was associated with the formation of cycle GMP. These effects were abolished by N(G)-nitro-L-arginine and methylene blue. Relaxations in response to ginsenoside Rg3 were unaffected by atropine, diphenhydramine, [D-Pro2, D-Trp7,9]substance P, propranolol, nifedipine, verapamil and glibenclamide but were markedly reduced by tetraethylammonium. Tetraethylammonium modestly reduced the relaxation induced by sodium nitroprusside. These findings indicate that ginsenoside Rg3 is a major mediator of the endothelium-dependent nitric oxide-mediated relaxation in response to ginsenosides in isolated rat aorta, possibly via activation of tetraethylammonium-sensitive K+ channels.

Bilateral kidney ligation abolishes pressor response to N(G)-nitro-D-arginine

We have shown that N(G)-nitro-D-arginine (D-NNA) is 50% as potent as N(G)-nitro-L-arginine (L-NNA) in causing pressor response and 2-3% as potent as L-NNA in inhibiting endothelium-dependent relaxation in vitro. These results suggest in vivo activation of D-NNA. Furthermore, the potency of D-NNA was markedly increased after it had been incubated with homogenate of the kidney, but not plasma or homogenate of the aorta, lungs or liver. This study examined if bilateral ligation of the kidneys attenuated the biological action of D-NNA. I.v. bolus of D-NNA (16 mg/kg), L-NNA (3 mg/kg) and norepinephrine (0.25-16 microg/kg) increased arterial pressure in sham-operated rats. Bilateral ligation of the kidneys abolished pressor response to D-NNA, but not L-NNA and norepinephrine. I.v. bolus D-NNA in sham-operated rats, but not kidney-ligated rats, inhibited relaxation response to acetylcholine in pre-constricted aortic rings ex vivo. These results indicate that the kidney is the primary organ which activates D-NNA.

Review article: the potential role of nitric oxide in chronic inflammatory bowel disorders

The aetiology of the chronic inflammatory bowel diseases-ulcerative colitis and Crohn's disease-as well as 'microscopic colitis'-both collagenous (COC) and lymphocytic colitis (LC)-remains unknown. Autoimmune mechanisms, cytokine polymorphism, commensal bacteria, infectious agents and vascular impairment have all been proposed as playing important roles in the pathogenesis of this spectrum of diseases. A variety of proinflammatory mediators, including tumour necrosis factor alpha, interleukin-1beta, interferon gamma, leukotriene B4 and platelet activating factor, promote the adherence of phagocytes to the venular endothelium and extravasation of these cells into the colonic mucosa. In addition to large amounts of nitric oxide (NO), injurious peroxynitrite may be formed in the epithelium by the inducible nitric oxide synthase (iNOS), which is considered to elicit cytotoxicity by the generation of superoxide with reduced L-arginine availability. In active ulcerative colitis, and to a lesser extent in Crohn's disease, a greatly increased production of NO has been demonstrated by indirect and direct measurements. Surprisingly, even higher rates of production have been observed in COC-a condition which is never associated with injurious inflammation. The latter observation favours the notion that NO promotes mucosal integrity. Further evidence for a protective role of NO in chronic inflammatory bowel disorders is provided by the observation of increased susceptibility to the induction of experi mental colitis in 'knock-out' mice deficient in iNOS. Selective inhibitors of iNOS activity, as well as topical L-arginine, may therefore prove beneficial in inflammatory bowel disease by reducing the production of superoxide by iNOS, while only the former option may be expected to reduce diarrhoea in chronic inflammatory bowel disorders. Clearly, further experimental work needs to be done before testing topical L-arginine in human inflammatory bowel disease.

Endothelium-derived relaxing, contracting and hyperpolarizing factors of mesenteric arteries of hypertensive and normotensive rats

Differences in the acetylcholine (ACh)-induced endothelium-dependent relaxation and hyperpolarization of the mesenteric arteries of Wistar Kyoto rats (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP) were studied. Relaxation was impaired in preparations from SHRSP and tendency to reverse the relaxation was observed at high concentrations of ACh in these preparations. Relaxation was partly blocked by NG-nitro-L-arginine (L-NOARG, 100 microM) and, in the presence of L-NOARG, tendency to reverse the relaxation was observed in response to higher concentrations of ACh, even in preparations from WKY. The relaxation remaining in the presence of L-NOARG was also smaller in preparations from SHRSP. The tendency to reverse the relaxation observed at higher concentrations of ACh in preparations from SHRSP or WKY in the presence of L-NOARG were abolished by indomethacin (10 microM). Elevating the K+ concentration of the incubation medium decreased relaxation in the presence of both indomethacin and L-NOARG. Relaxation in the presence of L-NOARG and indomethacin was reduced by the application of both apamin (5 microM) and charybdotoxin (0.1 microM). This suggests that the relaxation induced by ACh is brought about by both endothelium-derived relaxing factor (EDRF, nitric oxide (NO)) and hyperpolarizing factor (EDHF), which activates Ca2+-sensitive K+ channels. Electrophysiological measurement revealed that ACh induced endothelium-dependent hyperpolarization of the smooth muscle of both preparations in the presence of L-NOARG and indomethacin; the hyperpolarization being smaller in the preparation from SHRSP than that from WKY. These results suggest that the release of both NO and EDHF is reduced in preparations from SHRSP. In addition, indomethacin-sensitive endothelium-derived contracting factor (EDCF) is released from both preparations; the release being increased in preparations from SHRSP.

Effect of therapeutic concentrations of nitric oxide on bacterial growth in vitro

OBJECTIVES

Besides its vasodilative actions, nitric oxide (NO) is also involved in host defense on a cellular level. We studied the antimicrobial properties of NO in concentrations used with inhaled NO therapy for the treatment of pulmonary hypertension in neonates.

DESIGN

In vitro study of bacterial growth of five species, with and without NO exposure.

SETTING

Level IV neonatal intensive care unit at a university children's hospital.

SUBJECTS

In vitro bacterial cultures.

INTERVENTIONS

We tested ten different strains of five bacterial species (Staphylococcus aureus, Staphylococcus epidermidis, group B streptococcus [GBS/Streptococcus agalactiae], Escherichia coli, and Pseudomonas aeruginosa), derived from the tracheal isolates of ventilated premature and term infants. Cultures were exposed to three different concentrations of NO (40, 80, and 120 parts per million [ppm]) and bacterial growth was compared with the same strains incubated in ambient air for 24 hrs. After incubation (with or without NO), colony-forming units were counted.

MEASUREMENTS AND MAIN RESULTS

Bacterial growth of S. aureus, E. coli, and P. aeruginosa was not reduced with the NO concentrations applied. The number of colony-forming units of S. aureus increased at 80 ppm of NO. Growth of S. epidermidis and GBS was significantly affected at 120 ppm, resulting in decreased numbers of colony-forming units as compared with controls exposed to ambient air.

CONCLUSIONS

We conclude that NO has a selective bacteriostatic effect on some of those bacteria most commonly cultured in tracheal specimens of premature infants and neonates. This effect appears to be dose-dependent and occurs in the upper range of dosages used with inhaled NO therapy. However, in the range of dosages applied in ongoing controlled trials of inhaled NO in neonates and premature infants (1 to 80 ppm), a bacteriostatic effect of NO is not to be expected.

Endogenous asymmetrical dimethylarginine and hypertension associated with puromycin nephrosis in the rat

1. The present experiments were designed to investigate the role of asymmetrical NG,NG-dimethyl-L-arginine (ADMA) in causing hypertension associated with the focal and segmental glomerulosclerosis (FSGS) produced by a single bolus of puromycin aminonucleoside (PAN) and successive injection of protamine for 7 days in rats which had undergone unilateral nephrectomy. 2. After the unilateral nephrectomy, and administering PAN and protamine, histological examinations of the kidney revealed a typical FSGS, that is, evident abnormalities including segmental mesangial proliferation, obliteration of glomerular capillary lumens and adhesions between the glomerulus and Bowman's capsule could be observed. Changes in the glomerular epithelial cells consisted of the swelling with bleb formation. 3. In the FSGS rats, urine volume and urinary protein were significantly (P<0.05 and P<0.005) increased throughout 4-week experimental period, while the creatinine clearance was significantly (P<0.005) and transiently decreased, and recovered 4 weeks later. These changes were associated with the sustained elevation of the systolic blood pressure. 4. ADMA levels in aortic endothelial cells, plasma and urine were significantly (P<0.05 and P<0.005) increased in the FSGS rats, but the level in the kidney remained unchanged. 5. The basal level and net production of cyclic GMP in the aortic vessel wall with endothelium when stimulated by norepinephrine and acetylcholine were significantly (P<0.05 and P<0.01) attenuated in the FSGS rats. 6. There were significant and positive correlations between systolic blood pressure (y) and ADMA levels (x) in endothelial cells (y=4.43x+122.2, r=0.979, P<0.0001), plasma (y=0.10x+71.9, r=0.921, P<0.001) and urine (y=0.48x+126.9, r =0.699, P<0.005), but not significant in the kidney (y=0.06x+102.7, r=0.252, NS). 7. These findings suggest that ADMA as an endogenous inhibitor of NO synthesis may play an important role for the pathogenesis in the hypertension associated with the experimental FSGS in the rat.

Relaxant effects of L-citrulline in rabbit vascular smooth muscle

1. Vascular endothelium plays a pivotal role in the control of vascular tone through the release of vasoactive factors such as EDRF (NO). 2. The aim of this study was to investigate whether the addition of exogenous L-citrulline, the byproduct of the NO-synthesis, could relax vascular smooth muscle. 3. L-citrulline relaxed both endothelium-denuded and endothelium-intact rabbit aortic rings precontracted with noradrenaline 10(-6) M (maximum relaxations induced by L-citrulline 10(-8) M were 74.1+/-5.2% vs 51.3+/-2.8% in endothelium-denuded and endothelium-intact arteries, respectively). 4. This relaxant effect was enhanced by zaprinast (a phosphodiesterase type 5 inhibitor) and inhibited by HS-142-1 (a particulate guanylate cyclase inhibitor) and by apamin (a K(Ca)-channel blocker). 5. L-citrulline (10(-13)-10(-8) M) increased cGMP levels in aortic rings (maximum value with L-citrulline 10(-8) M was 0.165+/-0.010 pmol cGMP mg(-1) of tissue vs 0.038+/-0.009 pmol mg(-1) of tissue in basal). 6. L-citrulline as well as NO were released from endothelial cells in culture stimulated with ACh. The values were 6.50+/-0.50 microM vs 2.30+/-0.20 microM (stimulated with ACh and basal respectively) for L-citrulline and 4.22+/-0.10 microM vs 0.87+/-0.26 microM (stimulated with ACh and basal respectively) for NO. 7. These results suggest that L-citrulline could be released together with NO from endothelium and may have actions complementary to those of NO in the control of vascular smooth muscle relaxation.

LDLs impair vasomotor function of the coronary microcirculation: role of superoxide anions

Oxidized LDLs (Ox-LDLs) inhibit endothelium-dependent dilation of isolated conduit arteries in a manner comparable to the impairment demonstrated in atherosclerotic vessels. However, it is not known whether the microvessels, which do not develop atherosclerotic lesions, are susceptible to Ox-LDL. Since endothelial release of NO plays an important role in vasodilation and since its dysfunction associated with atherosclerosis has been shown to extend into the coronary microcirculation, we hypothesized that Ox-LDLs impair endothelium-dependent vasodilation of coronary arterioles by reducing the synthesis and/or release of NO. To test this hypothesis, porcine subepicardial vessels (50 to 100 microm) were isolated, cannulated, and pressurized to 60 cm H2O without flow for in vitro study. Isolated vessels developed basal tone and dilated in a dose-dependent manner to the endothelium-dependent vasodilators serotonin, ATP, and ionomycin. These vasodilatory responses were inhibited by the NO synthase inhibitor NG-monomethyl-L-arginine and were subsequently reversed by extraluminal administration of the NO precursor L-arginine (3 mmol/L), suggesting the involvement of NO in these vasomotor responses. Intraluminal incubation of the vessels with native LDL (N-LDL) or Ox-LDL (1 mg protein/mL) significantly attenuated dilations to serotonin, ATP, and ionomycin. Ox-LDL produced more severe inhibition than did N-LDL, and the inhibitory effect was comparable to that of NG-monomethyl-L-arginine. The inhibitory effects of N-LDL and Ox-LDL were reversed by exogenous L-arginine (3 mmol/L) and were prevented by sodium dihydroxybenzene disulfonate (Tiron), a cell-permeable superoxide scavenger. In contrast, administration of the cell-impermeable superoxide scavenger superoxide dismutase prevented the inhibitory effect of N-LDL but not of Ox-LDL. In addition, the inhibitory effects of LDL were not restored by D-arginine or by removal of intraluminal LDL. Neither N-LDL nor Ox-LDL altered endothelium-independent vasodilation to sodium nitroprusside. These results indicate that coronary arterioles are susceptible to LDLs that specifically impair endothelium-dependent vasodilation by reducing NO synthesis. It is suggested that the initiation of superoxide anion production and the subsequent L-arginine deficiency may be responsible for the detrimental effect of LDL.

Role of nitric oxide and prostaglandin in the protective effect of pibutidine hydrochloride, a novel histamine H2-receptor antagonist, on the gastric mucosal lesions in rats

1. The role of endogenous nitric oxide (NO) and prostaglandins (PGs) in the gastric mucosal protective action of pibutidine hydrochloride (IT-066), a novel histamine H2-receptor antagonist, was investigated in a 0.15 N hydrochloride (HCl) + 60% ethanol (EtOH)-induced gastric lesion model. 2. The 0.15 N HCl + 60% EtOH-induced lesion formation was reduced significantly by IT-066 (3 mg/kg, PO), NOR3 (spontaneous NO releaser; 0.03-0.1 mg/kg, SC) or PGE2 (0.01 mg/kg, PO) but was not reduced by famotidine (1-10 mg/kg, PO). 3. Pretreatment with NG-nitro-L-arginine methyl ester (L-NAME) (3 mg/kg, IV), an inhibitor of NO synthase, inhibited the protective action of IT-066 (3 mg/kg, PO), and the inhibitory effect of L-NAME was reversed by L-arginine (300 mg/kg, IV). The protective effect of PGE2 (0.01 mg/kg, PO) was not affected by the pretreatment with L-NAME (3 mg/kg, IV). 4. Infusion of carboxy-PTIO (1 mg/kg/min), a direct NO scavenger, inhibited the protective effect of IT-066 (3 mg/kg, SC) or NOR3 (0.1 mg/kg, SC). Pretreatment with indomethacin (5 mg/kg, SC) markedly reduced the protective effect of IT-066 (3 mg/kg, PO) or NOR3 (0.1 mg/kg, SC). 5. These results suggest that endogenous NO and PGs may be implicated in the gastric mucosal protection induced by IT-066 and that the endogenous PGs may contribute to the protective effect of NO.

[Inhaled nitric oxide in anesthesia and intensive care]

The role of endothelium in vascular relaxation is linked to the existence of endothelium derived relaxing factors (EDRF) known since 1980. In 1987, nitric oxide (NO) was identified as one of these factors. NO acts in many physiologic and pathophysiologic events. Atmospheric NO is a pollutant. Inhaled NO allows selective pulmonary vasodilation and is used to treat pulmonary artery hypertension (PAH). As inhaled NO is inactivated immediately in the blood by linking to haemoglobin, systemic vasodilation does not occur and right ventricular coronary perfusion pressure does not decrease. This is particularly important in the treatment of right ventricular failure due to PAH following cardiothoracic surgery. In patients with an acute respiratory distress syndrome (ARDS), inhaled NO improves the perfusion of adequately ventilated pulmonary territories. Very low concentrations of NO, such as two parts per million, decrease intrapulmonary venous admixture and may reverse hypoxaemia. However its long term benefits in ARDS must be assessed more accurately with multicentre controlled studies. Inhaled NO also improves refractory hypoxaemia in neonates. Its bronchodilatory effect, demonstrated experimentally, does not occur in acute obstructive bronchopulmonatory disease. The toxicity of NO, and overall of its oxidated derivative NO2 requires precise conditions of administration and close monitoring of inhaled fractions. In that case, the risk of NO toxicity seems very low when compared to its therapeutic benefits in selected patients.

Nitric oxide modulates cardiac contractility and oxygen consumption without changing contractile efficiency

Nitric oxide (NO) affects myocardial contractility and myocardial oxygen consumption (MVO2) in vitro. In alpha-chloralose-anesthetized dogs instrumented for the measurements of left ventricular (LV) pressure, LV volume using a conductance catheter, coronary blood flow, and coronary venous oxygen saturation (ScvO2) using a fiber-optic catheter, LV end-systolic pressure-volume relationships (ESPVR) and the relationship between MVO2 and LV pressure-volume area (PVA) were analyzed before and after intravenous infusions of the NO synthase inhibitor NG-monomethyl-L-arginine acetate (L-NMMA; 5 mg/kg, 8 dogs) and the NO substrate L-arginine (600 mg/kg, 7 dogs). L-NMMA increased the slope of the ESPVR (Emax) (P < 0.05) without changing contractile efficiency indicated by the inverse of the slope of the MVO2-PVA line. L-NMMA also increased unloaded MVO2, indicated by the y-axis intercept of the MVO2-PVA line (P < 0.05). In contrast, L-arginine decreased Emax (P < 0.05) while decreasing MVO2 (P < 0.05), and without changing contractile efficiency. The basal oxygen metabolism was not affected by L-NMMA and L-arginine. These data imply that endogenous NO spares MVO2 by reducing oxygen use in excitation-contraction coupling and attenuates cardiac contractility without changing contractile efficiency.

Neuropeptide Y and Y1-receptor agonists increase blood flow through arteriovenous anastomoses in rat tail

The purpose of this study was to characterize neuropeptide Y (NPY)-induced vasodilation in the rat tail. Sterile surgical technique was used (with pentobarbital sodium anesthesia) to equip rats with a jugular catheter and a blind-ended thermocouple reentrant tube next to the carotid artery. Tail skin and core temperature were measured with thermocouples during experiments. Tail skin blood flow was monitored with a laser Doppler flowmeter, and tail total blood flow and volume were measured with plethysmography. After baseline data were collected, saline, NPY (16, 32, 64, and 128 microg/kg), [Leu31 Pro34]NPY (63.25 microg/kg), or NPY[13-36] (44.7 microg/kg) was administered intravenously. Tail total blood flow, volume, and tail skin temperature increased, whereas tail skin blood flow and core temperature decreased in response to both NPY- and the Y1-receptor agonist [Leu31 Pro34]NPY but not in response to saline or NPY[13-36]. Studies conducted with the use of color microspheres demonstrated that arteriovenous anastomoses are involved in this NPY-induced vasodilation.

Acetylcholine-induced systemic vasodilation resistant to NG-nitro-L-arginine in an anaesthetized rats

1. The effects of NG-nitro-L-arginine (L-NNA; 20 mg/kg bodyweight (BW), i.v.) and metyrapone (300 mg/kg BW, s.c.) on acetylcholine (ACh)-induced depressor responses were investigated in anaesthetized rats. 2. Acetylcholine (0.05, 0.5, 5 micrograms/kg BW, i.v.) dose-dependently evoked a sharp fall in mean blood pressure (BP) followed by a slow recovery under control conditions. 3. Basal BP level was elevated when rats were treated with L-NNA, indicating endogenous nitric oxide (NO) participated in BP regulation. However, pretreatment with L-NNA did not attenuate but rather augmented the ACh-induced maximum vasodilation. In contrast, the time for recovery of mean BP to the pre-ACh administration level was shortened by L-NNA. These observations suggested that ACh-induced vasodilation consisted of two phases: a sharp and transient fall (phase 1) that was resistant to L-NNA followed by a longer depressor response (phase 2) that was suppressed by L-NNA. 4. To examine whether augmentation of phase 1 by L-NNA resulted from the elevation of basal BP, an appropriate dose of phenylephrine was infused to obtain similar BP elevation. Phenylephrine infusion augmented the phase 1 in a similar manner to L-NNA pretreatment but showed little effect on phase 2, supporting the selective inhibition of phase 2 by L-NNA. 5. The s.c. pretreatment with metyrapone for 3 days failed to attenuate phase 1. Thus, the involvement of endothelium-derived hyperpolarizing factor that could be formed by a metyrapone-sensitive oxidase in phase 1 was unlikely. 6. These results suggest that some factor(s), which is not inhibitable by L-NNA or metyrapone, may induce the phase 1 depressor response to ACh while NO is responsible for the phase 2 response. The mechanism inducing the phase 1 response remains to be identified.

Role of T lymphocytes and cytokines in coccidiosis

Development of a vaccine for avian coccidiosis has been hampered by lack of understanding of the various components of the host immune system leading to protective immunity. Clear understanding of the cellular dichotomy in cytokine production in mice and the availability of immunological reagents, as well as gene knock-out mice, now makes in-depth immunological study in this species feasible. From studies of various parasitic infection models in mice, it is becoming clear that complex regulation by cytokines is involved in host immunity. Furthermore, the studies in mice clearly indicated an important role of various effector mechanisms involving T lymphocytes, macrophages, natural killer (NK) cells and cytokines in resistance to coccidiosis. In comparative studies of coccidiosis in chickens, in-vivo and in-vitro studies revealed that interferon-gamma, tumor necrosis factor and transforming growth factor-beta are induced following Eimeria infection. Depletion studies revealed the importance of CD8+TCR-alpha-beta+ T lymphocytes in host protective immunity to avian coccidiosis. Taken together, studies in mice and chickens are providing a better understanding of the role of effector cells and soluble factors which control immune responses to Eimeria parasites.

Evidence for the presence of L-arginine-nitric oxide pathway in human red blood cells: relevance in the effects of red blood cells on platelet function

There is a renewed interest in the role of red blood cells (RBCs) in the regulation of vascular tone and platelet homeostasis. To examine whether human RBCs synthesize NO from L-arginine, which may mediate the antiplatelet effects of these cells, purified RBCs (10(7)-10(8)/ml) were incubated with [3H]L-arginine, and its conversion into [3H]L-citrulline determined. RBCs consistently converted [3H]L-arginine to [3H]L-citrulline in a Ca2+-dependent fashion, and this conversion was inhibited by two different specific NO synthase inhibitors. Suspension of RBCs (10(7)-10(8)/ml) reduced platelet aggregation, and the RBC-mediated inhibition of platelet aggregation was blocked by pretreatment of RBCs with NO synthase inhibitor and potentiated by pretreatment with superoxide dismutase. Release of serotonin by aggregating platelets also was inhibited in the presence of RBCs. Western analysis with a specific mouse monoclonal antibody provided direct evidence for the presence of human endothelium-type constitutive NO synthase with a molecular mass approximately 140 kDa in the RBC cytosol. These observations suggest that RBCs possess endothelium-type NO synthase and may regulate platelet function at least in part by in situ release of NO.

Nitric oxide: prospects and perspectives of in vivo detection by L-band EPR spectroscopy

This paper discusses, compares and evaluates various in vivo EPR methods of detection of nitric oxide (NO). In particular the various classes of agents are: Fe(II)-dithiocarbamate derivative complexes of MGD (N-methyl-D-glucamine dithiocarbamate) and DTCS [N-(dithiocarboxy)sarcosine], stable imidazolineoxy N-oxides and nitronyl N-oxides, and NO-sensitive chars. As a specific example direct, real-time, in vivo measurements of nitric oxide (NO) in mice are described with the water soluble metal chelator complex (MGD)2-Fe(II), as monitored at L-band EPR. The three-line EPR spectrum of [(MGD)2-Fe(II)-NO] was observed non-invasively in both control animals injected with the preformed product [(MGD)2-Fe(II)-NO] and from lipopolysaccharide (LPS) treated mice subsequently injected with (MGD)2-Fe(II) complex. The [(MGD)2-Fe(II)-NO] spectrum was markedly suppressed after administration of phenyl N-tert-butyl nitrone (PBN) prior to LPS injection as PBN inhibits the expression of inducible nitric oxide synthase (iNOS). When 15N-arginine was administered to LPS-treated mice, an EPR spectrum consisting of both three- and two-line EPR signals (due to (MGD)2-Fe(II)-14NO and (MGD)2-Fe(II)-15NO respectively) was observed, confirming that the trapped NO was generated through the NOS enzyme and not other chemical routes.

Effect of clenbuterol on non-endothelial nitric oxide release in rat mesenteric arteries and the involvement of beta-adrenoceptors

1. The aim of the present study was to explore the contribution of adrenergic, sensory and nitrergic innervations to the inhibitory effects of the beta2-adrenoceptor agonist clenbuterol on responses to electrical field stimulation (EFS, 200 mA, 0.3 ms, 1-16 Hz, for 30 s, at 1 min interval) in rat mesenteric artery segments without endothelium and the possible involvement of adrenergic, sensory and nitrergic innervations. 2. Clenbuterol (1 microM) reduced EFS-induced contractile responses, and this effect was reversed by the beta-antagonist propranolol (1 microM) (contraction at 16 Hz expressed as % of 75 mM K+-induced contraction was: control, 69+/-9, clenbuterol, 31+/-6, n=13, P<0.001; control, 83+/-5, clenbuterol+propranolol 70+/-7, n=11, P>0.05). 3. In arteries preincubated with [3H]-noradrenaline (NA), clenbuterol did not modify the tritium overflow evoked by EFS (200 mA, 0.3 ms, 4 Hz, for 60 s; ratio between tritium release in the second and first stimuli was: control, 0.80+/-0.05 and clenbuterol added before second stimulus, 0.91+/-0.11, n=5, P>0.05). 4. The nitric oxide (NO) synthase inhibitors NG-monomethyl-L-arginine (L-NMMA) and NG-nitro-L-arginine methyl ester (L-NAME) (10 and 100 microM), and the guanylate cyclase inhibitor methylene blue (10 microM) increased the contractions caused by EFS (% contraction at 16 Hz, control, 81+/-7, n=26; 10 microM L-NMMA, 109+/-12, n=8, P<0.05; methylene blue, 119+/-6, n=6, P<0.05). However, these contractions were decreased by the NO synthase substrate L-arginine 10 microM (14+/-6%, n=6, P<0.001), but not modified by either the sensory neurones toxin capsaicin (0.5 microM, 75+/-6%, n=6, P>0.05) or the protein synthesis inhibitor cycloheximide (10 microM, 83+/-6%, n=8, P>0.05). None of these drugs altered the concentration-response curves to exogenous NA (n=7). 5. Pretreatment with capsaicin or cycloheximide did not modify the reduction of the EFS-evoked contraction provoked by clenbuterol. However the presence of L-NMMA (or L-NAME) or methylene blue did decrease the effect of clenbuterol (% contraction at 16 Hz, clenbuterol, 31+/-6, n=13; clenbuterol+10 microM L-NMMA, 93+/-11, n=8, P<0.05; clenbuterol+methylene blue, 90+/-7, n=6, P<0.05). 6. These results suggest that the reduction caused by clenbuterol in the contraction induced by EFS in rat mesenteric arteries seems to be mediated by NO release, through the activation of beta2-adrenoceptors probably present on nitrergic nerves.

P1,P4-diadenosine 5' tetraphosphate induces nitric oxide release from bovine aortic endothelial cells

Since the infusion of P1,P4-diadenosine 5' tetraphosphate (Ap4A) into animal models induces vasodilation [1,2], the present study was performed to determine whether Ap4A induces the release of nitric oxide (NO) from endothelial cells. Ap4A induced NO release was 4.2-fold greater than the amount of NO released under basal condition. Ap4A induced NO release was inhibited by NG-nitro-L-arginine (L-NNA) and this inhibition was reversed by L-Arg. In addition, EGTA inhibits Ap4A induced NO release. These data are consistent with Ap4A inducing the release of NO from endothelial cells through the activation of endothelial nitric oxide synthase.

Interaction of endothelial eccrine mechanisms and human adrenomedullin on vascular resistance in canine bone

Adrenomedullin is a novel peptide known to be one of the most potent vascular smooth muscle relaxing agents in vivo. The aim of this study is to investigate the effect of adrenomedullin in relation to nitric oxide, prostaglandins and endothelium-derived hyperpolarized factor (EDHF). A 0.1-ml bolus of 1 nmol human adrenomedullin is a potent inhibitor of the pressor response to exogenous norepinephrine infusion in an ex vivo canine tibia perfusion model for a duration of at least 70 min (P < 0.005). This attenuation of vascular smooth muscle contraction occurs even when nitric oxide production is blocked by NG-monomethyl-L-arginine acetate (L-NMMA) infusion and EDHF is blocked by tetraethylammonium infusion, although the effect is of shorter duration (at least 10 min). Indomethacin as well does not affect the suppression of norepinephrine-induced vascular smooth muscle contraction. Based on these data, human adrenomedullin has both nitric oxide- and EDHF-dependent mechanism as well as a nitric oxide- and EDHF-independent mechanism.

Hemodialysis and L-arginine, but not D-arginine, correct renal failure-associated endothelial dysfunction

In end-stage renal failure (ESRF) symptomatic hemodialysis-related hypotension may prevent effective provision of renal replacement therapy. Endogenous inhibitors of nitric oxide synthase accumulate in ESRF and are cleared by dialysis. We, therefore, hypothesised that removal of these inhibitors by hemodialysis would increase endothelial nitric oxide generation and promote venodilation. In vivo responses of norepinephrine preconstricted dorsal hand veins to locally active doses of acetylcholine (an activator of nitric oxide synthase) and glyceryl trinitrate (GTN; a nitric oxide donor) were examined in patients undergoing maintenance hemodialysis for ESRF and in healthy age- and sex-matched controls. Patient studies were undertaken before and after dialysis. Studies before dialysis were repeated with co-infusion of either L-arginine or its inactive enantiomer D-arginine. Venodilation in response to acetylcholine was impaired before, and corrected by, dialysis whereas venodilation to GTN was similar before and after dialysis. Venodilation in response to acetylcholine before dialysis was restored by co-infusion of L- but not D-arginine. Therefore, patients with ESRF undergoing hemodialysis have impaired acetylcholine-mediated venodilation consistent with the accumulation in ESRF of functionally important inhibitors of nitric oxide synthase that are cleared by dialysis.

Heterogeneous cholinergic reactions of ringed seal coronary arteries

Coronary blood flow of some seal species is unusual in that it is highly variable in both non-diving and diving conditions and shows intermittent fluctuations, especially during dives when it frequently ceases for brief periods. We sought regulatory mechanisms governing these reactions by studying isometric tension recordings of isolated left circumflex (LC) and left anterior descending (LAD) coronary arteries of ringed seals, Phoca hispida, during reactions to a variety of agents for stimulating or blocking autonomic responses of the vascular smooth muscle. Micromolar acetylcholine (ACh) produced constriction of the small diameter segments of the LAD, but relaxation of the LC and larger segments of LAD. Both constrictions and dilations were prevented by atropine. Small vessel constriction by ACh was prevented by micromolar indomethacin and by a thromboxane receptor antagonist. Large vessel ACh dilations were prevented or reduced by rubbing off the endothelium and by the L-arginine analog, L-NG-nitro-arginine, an inhibitor of nitric oxide synthesis. We conclude that cholinergic, muscarinic, dilation of ringed seal large coronary arteries is mediated by endothelial-derived relaxing factor (EDRF), whereas ACh constriction of small arteries is mediated by a prostaglandin.

Endothelium-dependent vasorelaxing activity of aqueous extracts of Ilex paraguariensis on mesenteric arterial bed of rats

The effects of aqueous extracts of Ilex paraguariensis leaves (AEIp) were studied. Mesenteric arterial bed (MAB), precontracted by methoxamine with or without intact endothelium, was mounted on a tissue bath and exposed to plant extracts (bolus). The bolus injections of AEIp (300-1050 microg) significantly inhibited, in a concentration-dependent manner, the maximal contractile response induced by methoxamine (30 microm) in MAB. The endothelium-dependent relaxations were reversed by N(G)-nitro-L-arginine methyl ester (10 mM), whereas methylene blue (100 microM) was not capable of effectively inhibiting the AEIp-induced vasodilatation of MAB. The vasorelaxing effect of AEIp persisted in the presence of indomethacin (10 microM). These results suggest the involvement of NO of endothelial source (or others factors) in this vasodilatory effect.

Early effects of acute gamma-radiation on vascular arterial tone

1. To determine the acute effects of irradiation on the functionality of vessel, rat aortic rings were mounted in an organ bath for isometric tension measurements and irradiated (60Co, 1 Gy min(-1), 15 min). 2. Irradiation, which is without effect on non-contracted or endothelium-denuded vessels, led to an immediate and reversible increase in vascular tone on (-)-phenylephrine (1 microM)-precontracted aortic rings. The tension reached a plateau about 5 min after the beginning of irradiation. 3. The maximal radiation-induced contraction occurred on aortic rings relaxed by acetylcholine (ACh) (1 microM). In this condition, the addition of catalase (1000 u ml(-1)), which reduces hydrogen peroxide, and DMSO (0.1% v/v), which scavenges hydroxyl radical, had no influence on tension level while superoxide dismutase (SOD) (100 u ml(-1)), a superoxide anion scavenger, reduced the observed contraction. A similar result was obtained in the presence of indomethacin (10 microM), a cyclo-oxygenase blocker. 4. Pretreatment of rings with the nitric oxide synthase inhibitor, N(omega)-nitro-L-arginine methyl ester (L-NAME) (10-100 microM) inhibited the radiation-induced contraction. 5. This effect was dose rate-dependent and even occurred for a very low dose rate (0.06 Gy min(-1)). 6. The present results indicate that gamma-radiation induces an instantaneous vascular tone increase that is endothelium and dose rate-dependent. This effect is (i) maximal when nitric oxide (NO) is produced, (ii) greatly reduced by SOD and (iii) inhibited by L-NAME, suggesting a major involvement of complexes between NO and superoxide anion.

The effects of L-arginine and iloprost on the viability of random skin flaps in rats

The effects of an intravenous infusion of L-arginine as a physiological precursor of endothelium-derived relaxing factor/nitric oxide (EDRF/NO), iloprost (a stable prostacyclin (PGI2) analogue), and L-arginine combined with iloprost on skin viability were studied in 9 x 3 cm random pattern skin flaps in rats. Intravenous infusion of all drugs was started at the beginning of the operation and continued for 60 minutes. At the end of infusion period the depth of fluorescein dye penetration in the skin flap was assessed visually from photographic records, and the flap survival area was measured by the grid method at the seventh postoperative day. There was a significant reduction in distal necrosis of random skin flaps after intravenous infusion of L-arginine, iloprost, and L-arginine combined with iloprost (p < 0.01). Possible mechanisms that may be responsible for impairment of endothelium-dependent vasodilation and vasospasm in the microvasculature of random skin flap and their prevention with L-arginine and iloprost include restoration of the depleted stores of NO which in turn causes vasodilatation and has an antithrombotic effect.

Importance of nitric oxide and capsaicin-sensitive afferent nerves in healing of stress lesions induced by epidermal growth factor

Epidermal growth factor (EGF) is a potent mitogen implicated in gastroprotection and ulcer healing, but its possible interaction with nitric oxide (NO) and sensory nerves on healing after acute gastric damage has not been assessed. We examined the effects of topical application of a small dose (0.5 mg/kg) of capsaicin to stimulate sensory nerves and a larger parenteral dose of capsaicin (125 mg/kg s.c.) to deactivate these neurons or the effect of systemic administration of NG-nitro-L-arginine methyl ester (L-NAME) (20 mg/kg i.v.) to suppress NO synthase on healing of gastric lesions induced by 3.5 h of water immersion and restraint stress (WRS) in rats without or with EGF administration. Rats were sacrificed at 0, 6, 12, or 24 h after WRS and the gastric blood flow (GBF) was measured by the H2 gas clearance technique. Exposure to WRS produced many gastric lesions, with a marked decrease in GBF, but at 12 h these lesions started to heal and the lesion number was reduced by 75% after 24 h. This was accompanied by progressive increase in the GBF and an increase in expression of EGF mRNA in gastric mucosa, as detected by RT-PCR. Pretreatment with L-NAME or functional ablation of sensory nerves by capsaicin significantly delayed the healing of WRS lesions and accompanying hyperemia. In contrast, pretreatment with EGF (100 micrograms/kg s.c.) or glyceryl trinitrate (10 mg/kg i.g.), a donor of NO, or stimulation of sensory nerves by topical capsaicin significantly enhanced the healing of these lesions and increased the GBF. The acceleration of the healing and accompanying hyperemia induced by EGF at 12 h after WRS were completely reversed in rats pretreated with L-NAME or in those with capsaicin denervation. Addition of L-arginine but not D-arginine to L-NAME restored the healing of stress lesions and gastric hyperemia induced by this peptide. Removal of salivary glands, which reduced luminal content of EGF and DNA synthesis by about fourfold compared to rats with intact glands, produced a significant delay in healing, and this was further aggravated by capsaicin denervation. We conclude that EGF, sensory nerves, and NO play an important role in the healing of gastric mucosa from lesions induced by stress and that sensory nerves and NO appear to interact with EGF in the mechanism of mucosal recovery from stress lesions.

Bradykinin-induced release of nitric oxide by the isolated perfused rat heart: importance of preformed pools of nitric oxide-containing factors

OBJECTIVE

To study whether the vasorelaxant effect of bradykinin in the coronary vascular bed depends on the release of NO from preformed pools and/or de-novo synthesis of NO resulting from bradykinin-induced stimulation of NO synthase.

DESIGN AND METHODS

Rat hearts were perfused according to Langendorff's method. Coronary flow was measured continuously. We constructed concentration-response curves for bradykinin and L-arginine under control conditions, after downregulation of NO synthase by exposing the heart to high concentrations (10 mmol/l) of NO and during chronic inhibition of NO synthase, obtained by perfusing the heart for 30 min with 0.1 mmol/l N(omega)-nitro-L-arginine methyl ester. The effect of acute inhibition of NO synthase was studied by infusing single submaximal doses of bradykinin and of L-arginine in the absence and presence of 0.1 mmol/l N(omega)-nitro-L-arginine methyl ester.

RESULTS

Coronary flow [baseline 9 +/- 2 ml/min (mean +/- SD)] increased to maximally 23 +/- 6 ml/min with bradykinin and to 16 +/- 4 ml/min with L-arginine. Maximal coronary flow, established as the maximal effect in response to NO, was 22 +/- 4 ml/min. Chronic inhibition of NO synthase reduced coronary flow to 4 +/- 1 ml/min. Coronary flow did not change after downregulation of NO synthase by NO. Neither downregulation nor acute inhibition of NO synthase affected the response to bradykinin, whereas chronic inhibition of NO synthase blocked the bradykinin-induced increase in coronary flow by > 90%. Administration of L-arginine no longer increased coronary flow under all tested conditions.

CONCLUSIONS

Preformed pools of NO-containing factors exist within the isolated perfused heart and bradykinin exerts its vasorelaxant effects at least in part by the mobilization of these preformed pools. These data may reconcile previous discrepancies about the (lack of) effect of NO synthase inhibitors on bradykinin-induced coronary vasodilatation.

Modulatory role of endothelial calcium level in vascular tension of canine depolarized coronary arteries

The vascular tension in the coronary artery is modulated by factors released by endothelial cells. We investigated the relationship between the Ca2+ level in endothelium and endothelium-mediated changes in smooth muscle tone in high K(+)-depolarized canine coronary arteries by measuring intracellular Ca2+ concentration fluorimetrically with the Ca2+ indicator fura 2. Addition of Ca2+ (1 mM) caused an increase in endothelial Ca2+ and relaxed the 30 mM K(+)-depolarized arteries following inhibition of Ca2+ influx in the smooth muscle with diltiazem. This relaxation was inhibited by NG-monomethyl-L-arginine. As extracellular K+ concentration was decreased, increases of endothelial Ca2+ were augmented, whereas the relaxation was decreased. Basal muscle tone was found to be decreased in low K+ by measuring relaxation by sodium nitroprusside. These results suggest the importance of Ca2+ level in the endothelium in playing a modulatory role in coronary tension through the production of nitric oxide. The correlation of extracellular K+ to Ca2+ level in the endothelium indicates a typical characteristic of the passive Ca2+ entry pathway in the endothelium, whereas the resultant relaxation appears to be restricted by the basal muscle tone.

Nitric oxide as neuromodulator of sympathetic transmission in rat vas deferens

1. Electrical field stimulation (EFS) of muscle strips in vitro elicited a tetrodotoxin (TTX)-sensitive biphasic contractile response consisting of a phasic component followed by a tonic one. 2. The amplitude of both components of the response was impaired by N omega-nitro-L-arginine and potentiated by sodium nitroprusside. Cystamine caused a reduction in amplitude of both phasic and tonic components of the response to EFS. Neither N omega-nitro-L-arginine, sodium nitroprusside, nor cystamine induced changes in the resting muscle tone, or in the contractile response to exogenous agonists ATP and noradrenaline (NA). 3. The nitric oxide scavenger, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, induced a reduction in amplitude of both components of the response to EFS. 4. These results reveal a facilitatory prejunctional modulatory role for nitric oxide in sympathetic neurotransmission in rat vas deferens. Endogenous nitric oxide released in the extracellular space is presumed to potentiate neurotransmission by acting at prejunctional level via cGMP.

The role of endothelial nitric oxide synthase expression in the development of pulmonary hypertension in chronically hypoxic infant swine

OBJECTIVE

Our goal was to determine the role of pulmonary endothelial nitric oxide synthase expression in the development of pulmonary hypertension in infants with congenital cyanotic heart disease.

METHODS

Two groups of 4-week-old piglets were studied. In one group, the piglets were raised in an environment of 10% oxygen from 2 days of age (cyanotic, n = 6), and in the other group the piglets were raised at room air (control, n = 5). Pulmonary hemodynamics were measured in vivo for each animal, and peripheral lung biopsy specimens were obtained for Western blot analysis with the use of antiendothelial nitric oxide synthase antibody and for activity analysis with the use of the tritiated L-arginine assay.

RESULTS

The piglets in the chronically hypoxic group had significant increases in mean pulmonary arterial pressure (44.0 +/- 3.8 mm Hg vs 14.8 +/- 1.2 mm Hg in controls, p = 0.0007) and pulmonary vascular resistance (7272.0 +/- 871.1 dyne x cm x sec(-5) vs 1844.5 +/- 271.2 dyne x cm x sec(-5) in controls, p = 0.002). These changes in the pulmonary hemodynamics of the hypoxic piglets were accompanied by a twofold increase in the expression of pulmonary endothelial nitric oxide synthase (p = 0.0043) but no corresponding increase in nitric oxide synthase activity.

CONCLUSIONS

Raising infant piglets in an environment of 10% oxygen for 4 weeks results in significant pulmonary arterial hypertension accompanied by increased expression of nitric oxide synthase within the lung endothelium. Furthermore, the increased levels of nitric oxide synthase within the lungs of the hypoxic swine were not accompanied by a proportional increase in enzyme activity. These findings suggest that the development of pulmonary hypertension in infants with congenital cyanotic disease is not due to decreased expression of endothelial nitric oxide synthase, but instead may be related to a decreased ability of the enzyme to produce sufficient nitric oxide.

Decreased endothelium-dependent vasoconstriction to noradrenaline in acute-stressed rats is potentiated by previous chronic stress: nitric oxide involvement

1. The objective was to determine whether nitric oxide participates in stress adaptive responses. Acute stress (AS) decreased endothelium-dependent vasoconstriction to noradrenaline (NA) in rat aorta [control rat (CR) 3.90 +/- 0.18, n = 22; AS 2.76 +/- 0.20, n = 13; P < 0.05]. 2. Chronic stress exposure previous to AS (CS) potentiated this effect [CS 1.93 +/- 0.19; n = 9; P < 0.05 related to CR, P < 0.05 related to AS]. 3. Methylene blue and NG-monomethyl-L-arginine, but not indomethacin, restored the decreased aorta reactivity to NA. 4. No reactivity alteration was observed in aorta without endothelium either in both stress conditions or in the presence of inhibitors. These data show that the nitric oxide participates in stress responses.

N-arachidonylethanolamide relaxation of bovine coronary artery is not mediated by CB1 cannabinoid receptor

It has been reported that the endogenous cannabinoid N-arachidonylethanolamide (AEA), commonly referred to as anandamide, has the characteristics of an endothelium-derived hyperpolarizing factor in rat mesenteric artery. We have carried out studies to determine whether AEA affects coronary vascular tone. The vasorelaxant effects of AEA were determined in isolated bovine coronary artery rings precontracted with U-46619 (3 x 10(-9) M). AEA decreased isometric tension, producing a maximal relaxation of 51 +/- 9% at a concentration of 10(-5) M. Endothelium-denuded coronary arteries were not significantly affected by AEA. The CB1 receptor antagonist SR-141716A (10(-6)M) failed to reduce the vasodilatory effects of AEA, suggesting that the CB1 receptor is not involved in this action of AEA. Because AEA is rapidly converted to arachidonic acid and ethanolamine in brain and liver by a fatty acid amide hydrolase (FAAH), we hypothesized that the vasodilatory effect of AEA results from its hydrolysis to arachidonic acid followed by enzymatic conversion to vasodilatory eicosanoids. In support of this hypothesis, bovine coronary arteries incubated with [3H]AEA for 30 min hydrolyzed 15% of added substrate; approximately 9% of the radiolabeled product was free arachidonic acid, and 6% comigrated with the prostaglandins (PGs) and epoxyeicosatrienoic acids (EETs). A similar result was obtained in cultured bovine coronary endothelial cells. Inhibition of the FAAH with diazomethylarachidonyl ketone blocked both the metabolism of [3H]AEA and the relaxations to AEA. Whole vessel and cultured endothelial cells prelabeled with [3H]arachidonic acid synthesized [3H]PGs and [3H]EETs, but not [3H]AEA, in response to A-23187. Furthermore, SR-141716A attenuated A-23187-stimulated release of [3H]arachidonic acid, suggesting that it may have actions other than inhibition of CB1 receptor. These experiments suggest that AEA produces endothelium-dependent vasorelaxation as a result of its catabolism to arachidonic acid followed by conversion to vasodilatory eicosanoids such as prostacyclin or the EETs.

Impairment and restoration of nitric oxide-dependent vasodilation in cardiovascular disease

The generation of nitric oxide by the vascular endothelium maintains a continuous vasodilator tone that is essential for the regulation of blood flow and blood pressure. Nitric oxide also contributes to the control of platelet aggregation and has important antiatherogenic effects. These properties are mediated by the action of constitutive nitric oxide synthase and subsequent activation by nitric oxide of soluble guanylate cyclase. Impaired release of nitric oxide occurs in most animal and human models of hypertension, contributing to the increased peripheral resistance and most likely to the development of cardiovascular complications. Antihypertensive medications (angiotensin-converting enzyme [ACE] inhibitors and calcium channel blockers) appear to prevent the impairment of nitric oxide-mediated vasodilation in experimental hypertension, though in humans the data are not as clear. Reduced nitric oxide release appears therefore to be a consequence rather than a cause of high blood pressure, and the reduction in blood pressure per se is most important. In hyperlipidaemia, endothelium-dependent relaxations are reduced probably due to the inhibitory action of oxidized low-density lipoproteins on endothelium-dependent relaxations. Lipid-lowering strategies and, more recently, ACE inhibition have been demonstrated to improve nitric oxide dependent coronary vasodilation in hypercholesterolaemic patients with and without atheromatous coronary disease. Nitric oxide dependent vasodilation is also impaired in insulin- and non-insulin-dependent diabetes as well as in healthy aging. Endothelial dysfunction may be improved in non-insulin-dependent diabetes by administration of the antioxidants, supporting the hypothesis that nitric oxide inactivation by oxygen-derived free radicals contributes to abnormal vascular reactivity in diabetes.

Pathway-specific effects of calcitonin gene-related peptide on irideal arterioles of the rat

1. Arteriolar diameter and membrane voltage have been measured to investigate the actions of calcitonin gene-related peptide (CGRP) in rat irideal arterioles. 2. Activation of sensory nerves inhibited sympathetic vasoconstriction, reduced the accompanying 40-50 mV depolarization by 90% and caused a 4 mV hyperpolarization. 3. The inhibition of vasoconstriction was prevented by either preincubation in L-NAME (10 microM), to inhibit nitric oxide production, by preincubation in the cell-permeant adenylate cyclase inhibitor dideoxyadenosine (1 mM) or by preincubation in the ATP-sensitive potassium channel blocker glibenclamide (10 microM). The subsequent addition of a nitric oxide donor to the glibenclamide solution inhibited nerve-mediated vasoconstriction, suggesting that the potassium channel involvement preceded the production of nitric oxide. The small hyperpolarization was not affected by L-NAME. 4. Nerve-mediated vasodilatation persisted in the presence of L-NAME (10 microM) but was abolished with the CGRP1 receptor antagonist CGRPS-37. 5. In arterioles preconstricted with the alpha 2-adrenoceptor agonist UK-14304 (100 nM), exogenous CGRP caused a hyperpolarization and a dose-dependent vasodilatation, neither of which was affected by L-NAME (10 microM). 6. In arterioles preconstricted with 30 mM KCl, CGRP (10 nM) caused vasodilatation but not hyperpolarization, suggesting that the hyperpolarization was not causal to the vasodilatation. 7. Forskolin (30 nM), in the presence of L-NAME to present effects due to nitric oxide, caused vasodilatation. 8. These results suggest that CGRP inhibits sympathetic nerve-mediated vasoconstriction through sequential increases in cyclic AMP and nitric oxide, while vasodilatation results from increases in cyclic AMP alone. The production of nitric oxide, but not its mechanism of action, appears to be dependent on the activation of ATP-sensitive potassium channels. The possible sites of action of these two pathways are discussed.

A caveolar complex between the cationic amino acid transporter 1 and endothelial nitric-oxide synthase may explain the "arginine paradox"

Immunohistochemistry of porcine pulmonary artery endothelial cells (PAEC) with antibodies specific for caveolin, endothelial nitric-oxide synthase (eNOS), and the arginine transporter (CAT1) demonstrates that all of these proteins co-localize in plasma membrane caveolae. When incubated with solubilized PAEC plasma membrane proteins, eNOS-specific antibody immunoprecipitates CAT1-mediated arginine transport. These results document the existence of a caveolar complex between CAT1 and eNOS in PAEC that provides a mechanism for the directed delivery of substrate arginine to eNOS. Direct transfer of extracellular arginine to membrane-bound eNOS accounts for the "arginine paradox" and explains why caveolar localization of eNOS is required for optimal nitric oxide production by endothelial cells.

Lead-induced hypertension: interplay of nitric oxide and reactive oxygen species

An elevation of mean blood pressure was found in rats treated with low lead (0.01% lead acetate) for 3 months, as contrasted to paired Sprague-Dawley control rats. In these rats, measurement of plasma and urine endothelins-1 and -3 revealed that plasma concentration and urinary excretion of endothelin-3 increased significantly after 3 months (plasma: lead group, 31.8+/-2.2, versus controls, 23.0+1.7 pg/mL, P<.001; urinary excretion: lead group, 46.6+11.7, versus controls, 35.6+6.7 pg/24 h, P<.05), whereas endothelin-1 was unaffected. Plasma and urinary nitric oxide (NO) and cyclic GMP concentrations were not significantly changed. However, assay of plasma and kidney cortex malondialdehyde by high-pressure liquid chromatography, as a measure of reactive oxygen species, was elevated in lead-treated rats compared with that in control rats (plasma: lead group, 4.74+1.27, versus controls, 2.14+.49 micromol/L, P<.001; kidney cortex: lead group, 28.75+3.46, versus controls, 16.38+2.37 nmol/g wet weight, P<.001). There was increased NO synthase activity in lead-treated rat brain cortex and cerebellum. In lead-treated rat kidney cortex, the endothelial constitutive NO synthase protein mass was unaffected, whereas the inducible NO synthase protein mass was increased. These data suggest a balance between increased NO synthesis and degradation (by reactive oxygen species) in lead-treated rats, which results in normal levels of NO. Thus, the hypertension may be related to an increase in the pressure substances, endothelin-3 and reactive oxygen species, rather than to an absolute decrease in nitric NO.

Role of nitric oxide in the regulation of the hepatic microcirculation in vivo

BACKGROUND/AIMS

Nitric oxide (NO) is an important mediator in the regulation of vascular tone. However, no data exist on the physiological role of NO in the regulation of the hepatic microcirculation. This study was designed to evaluate the role of NO in the hepatic microcirculation in vivo under physiological conditions.

METHODS

The hepatic microcirculation was investigated in anesthetized rats by intravital fluorescence microscopy after injection of fluorescein-isothiocyanate-labeled erythrocytes. Following assessment of baseline sinusoidal perfusion, animals were randomly treated with L-NMMA (n=6), L-arginine (n=6), nitroprusside sodium (NPS, n=5) or a comparable volume of NaCl (n=4). Drugs were given through a portal vein catheter at three doses (Dx), each followed by intravital microscopy. L-NMMA was given: 5 mg/kg (D1), 25 mg/kg (D2), 50 mg/kg (D3); L-arginine 30 mg/kg (D1), 150 mg/kg (D2), 300 mg/kg (D3); and NPS continuously 80 microg x kg(-1) x h(-1).

RESULTS

L-NMMA induced a significant increase of mean arterial blood pressure (MAP) (114 vs. 129 mm Hg; p<0.05). In contrast, MAP of NPS-treated animals decreased (107 vs. 91 mm Hg; p<0.01) whereas MAP of animals receiving L-arginine did not significantly differ. Sinusoidal blood flow revealed dose-dependent changes: L-NMMA significantly decreased perfusion of sinusoids (D1: 65%, D2: 57%, D3: 50% of baseline, p<0.05). Injection of L-arginine increased the sinusoidal flow even with the lowest dose (D1: 137%, D2: 133%, D3: 123%, p<0.05). Continuous infusion of NPS had little effect on sinusoidal blood flow at the first and second times of microscopy but sinusoidal blood flow was significantly increased at the third time (D1: 103%, D2: 106%, D3: 122%).

CONCLUSIONS

Inhibition of NOS results in a dose-dependent disturbance of the hepatic microcirculation despite significantly increased MAP, whereas L-arginine increases the sinusoidal blood flow. The results indicate an important role for NO in the regulatory mechanisms of hepatic sinusoidal perfusion under physiological conditions.

Hyperpolarizing factors

There is now overwhelming evidence for factors, other than nitric oxide (NO), that mediate endothelium-dependent vasodilation by hyperpolarizing the underlying smooth muscle via activation of Ca2+-activated K+ channels. Although the identity of endothelium-derived hyperpolarizing factor (EDHF) remains to be established, cytochrome P450 (CYP)-dependent metabolites of arachidonic acid (AA), namely, the epoxides, fulfill several of the criteria required for consideration as putative mediators of endothelium-dependent hyperpolarization. They are produced by the endothelium, released in response to vasoactive hormones, and elicit vasorelaxation via stimulation of Ca2+-activated K+ channels. Our studies in the rat indicate that, of the epoxides, 5,6-epoxyeicosatrienoic acid (5,6-EET) is the most likely mediator of NO-independent, but CYP-dependent coronary vasodilation in response to bradykinin. Studies in the rat kidney, however, support the existence of additional EDHFs as acetylcholine also exhibits NO-independent vasodilation that is unaffected by CYP inhibitors in concentrations that attenuate responses to bradykinin. In some blood vessels, NO may tonically suppress the expression of CYP-dependent EDHF. In the event of impaired NO synthesis, therefore, a CYP-dependent vasodilator mechanism may serve as a backup to a primary NO-dependent mechanism, although they may act in concert. In other vessels, particularly microvessels, an EDHF may constitute the major vasodilator mechanism for hormones and other physiological stimuli. EDHFs appear to be important regulators of vascular tone; alterations in this system can be demonstrated in hypertension and diabetes, conditions associated with altered endothelium-dependent vasodilator responsiveness.

Acute effects of nitric oxide blockade with L-NAME on arterial haemodynamics in the rat

1. We employed the technique of impedance spectral analysis to investigate the role of endogenous nitric oxide (NO) in the regulation of steady and pulsatile haemodynamics in Wistar Kyoto rat (WKY). 2. A total of 12 WKYs was anaesthetized with pentobarbitol sodium (40 mg kg-1, i.p.) and artificially ventilated with an animal respirator. The aortic pressure wave was monitored with a high fidelity Millar sensor, and aortic flow wave with an electromagnetic flow probe. The pressure and flow waves were subjected to Fourier transform for the analysis of impedance spectra. 3. The baseline cardiovascular parameters were mean arterial pressure (APm) 95 +/- 9 mmHg, heart rate (HR) 338 +/- 9 b.p.m., stroke volume (SV) 0.23 +/- 0.01 ml, cardiac output (CO) 77.8 +/- 1.6 ml min-1, total peripheral resistance (TPR) 98 +/- 11 (x10(3)) dyne s cm-5, characteristic impedance (Zc) 2046 +/- 141 dyne s cm-5, arterial compliance at mean AP (Cm) 3.78 +/- 0.22 microliters mmHg-1 and backward pulse wave (Pb) 12.9 +/- 0.6 mmHg. 4. An NO synthase inhibitor, NG-nitro-L-arginine monomethyl ester (L-NAME) was administered at graded intravenous doses. This agent caused dose-dependent increases in AP and TPR with decreases in HR. At an accumulative dose of 10 mg kg-1, APm was increased by 29 +/- 3 mmHg (+31%) and TPR by 49 +/- 6 (x10(3)) dyne s cm-5 (+50%), while HR was reduced by 37 +/- 5 b.p.m. (-11%) and CO by 10.4 +/- 0.8 ml min-1 (-14%). The pulsatile haemodynamics including Zc and Pb were slightly increased by 14-15%. Cm was decreased by 1.09 microliters mmHg-1 (-29%). L-NAME also did not significantly affect the ventricular work including the steady, oscillatory and total work. 5. Aminoguanidine, a specific inhibitor for inducible NO synthase (iNOS), in dose 10-60 mg kg-1 i.v. did not alter the AP, HR and other parameters. The result indicated that blockade of constitutive NOS, but not iNOS is involved in these changes. 6. Angiotensin II (Ang) in various infusion doses was used to produce a profile of AP increase similar to that caused by L-NAME. Ang remarkably increased Zc, while TPR was moderately elevated. The pattern of haemodynamic changes was different from that following L-NAME. 7. The results suggest that blockade of the endogenous NO affects predominantly the arterial pressure and peripheral resistance. The Windkessel functions such as arterial impedance and pulse wave reflection are slightly increased. Ventricular works are not significantly altered.

Effect of methylguanidine, guanidine and structurally related compounds on constitutive and inducible nitric oxide synthase activity

The inhibitory activity of methylguanidine, guanidine and their precursors, creatine and creatinine, on both the neuronal constitutive and lung inducible isoforms of nitric oxide synthase were examined in this study. Methylguanidine and guanidine (0.01-3 mM) significantly (P<0.01) inhibited in a concentration-dependent manner both isoforms of the enzyme. Furthermore analysis of the inhibition curves by ANOVA revealed that methylguanidine and guanidine act as non selective inhibitors of both nitric oxide synthases (P>0.4 for both methylguanidine and guanidine). In contrast, creatine and creatinine, although containing guanidine group, were totally ineffective on either enzyme even at concentration up to 3 mM. The results obtained for tested compounds also suggest a role for the lateral chain of guanidine group in the enzyme inhibition. The lack of selectivity of methylguanidine and guanidine in inhibiting both the nitric oxide synthase enzymes could account for some pathological manifestations like neurological disorders, host defense impairment and probably hypertension, that often occur in patients with uremia or chronic renal failure.

Basal nitric oxide production is not reduced in patients with noninsulin-dependent diabetes mellitus

Vascular disease is the leading cause of morbidity, disability and death in patients with noninsulin-dependent diabetes mellitus. Abnormalities in endothelium-derived nitric oxide (NO) have been demonstrated to be involved in the pathogenesis of vascular disease. By measuring hemodynamic responses to a NO synthase agonist or antagonist, previous studies have shown the presence of NO deficiency in patients with noninsulin-dependent diabetes mellitus, a method of assessing bioactive NO formation. However, direct biochemical evidence that this is the case, has not been produced. In vivo NO is metabolized into nitrate, an end breakdown product of NO, which can be used as an index of endogenous NO formation. To investigate further whether decreased basal synthesis of NO may be a major cause of endothelium-mediated vascular dysfunction in patients with noninsulin-dependent diabetes mellitus, the plasma nitrite/nitrate levels of 15 patients were examined and compared with 13 normal controls. The results showed that in basal conditions plasma nitrite/nitrate levels were not reduced in diabetic patients compared with normal controls (37.3 +/- 14.7 versus 29.4 +/- 8.6 mumol/l). It was concluded that in noninsulin-dependent diabetes mellitus patients, endothelium-derived basal NO formation is not impaired. This study, taken with previous observations, suggests that factors other than diminished basal NO production, such as reduced bioavailability of NO probably due to the augmented production of superoxide anion with subsequently increased inactivation of NO, contribute to the high incidence of vascular disease in patients with noninsulin-dependent diabetes mellitus.

Effect of L-arginine on human coronary endothelium-dependent and physiologic vasodilation

OBJECTIVES

We hypothesized that L-arginine would improve abnormal coronary vasodilation in response to physiologic stress in patients with atherosclerosis and its risk factors by reversing coronary endothelial dysfunction.

BACKGROUND

Studies have demonstrated that physiologic coronary vasodilation correlates with endothelial function and that L-arginine, the substrate for nitric oxide synthesis, improves the response to acetylcholine (Ach).

METHODS

Changes in coronary blood flow and epicardial diameter response to Ach, adenosine and cardiac pacing were measured in 32 patients with coronary atherosclerosis or its risk factors and in 7 patients without risk factors and normal coronary angiograms.

RESULTS

Intracoronary L-arginine did not alter baseline coronary vascular tone, but the epicardial and microvascular responses to Ach were enhanced (both p < 0.001). The improvement after L-arginine was greater in epicardial segments that initially constricted with Ach; similarly, L-arginine abolished microvascular constriction produced by higher doses of Ach. Thus, there was a negative correlation between the initial epicardial and vascular resistance responses to Ach and the magnitude of improvement with L-arginine (r = -0.55 and r = -0.50, respectively, p < 0.001). D-Arginine did not affect the responses to Ach, and adenosine responses were unchanged with L-arginine. Cardiac pacing-induced epicardial constriction was abolished by L-arginine, but microvascular dilation remained unaffected.

CONCLUSIONS

Thus, L-arginine improved endothelium-dependent coronary epicardial and microvascular function in patients with endothelial dysfunction. Prevention of epicardial constriction during physiologic stress by L-arginine in patients with endothelial dysfunction may be of therapeutic value in the treatment of myocardial ischemia.

Nitric oxide primes pancreatic beta cells for Fas-mediated destruction in insulin-dependent diabetes mellitus

Fas is an apoptosis-inducing surface receptor involved in controlling tissue homeostasis and function at multiple sites. Here we show that beta cells from the pancreata of newly diagnosed insulin-dependent diabetes mellitus (IDDM) patients express Fas and show extensive apoptosis among those cells located in proximity to Fas ligand-expressing T lymphocytes infiltrating the IDDM islets. Normal human pancreatic beta cells that do not constitutively express Fas, become strongly Fas positive after interleuken (IL)-1beta exposure, and are then susceptible to Fas-mediated apoptosis. NG-monomethyl-L-arginine, an inhibitor of nitric oxide (NO) synthase, prevents IL-1beta-induced Fas expression, whereas the NO donors sodium nitroprusside and nitric oxide releasing compound (NOC)-18, induce functional Fas expression in normal pancreatic beta cells. These findings suggest that NO-mediated upregulation of Fas contributes to pancreatic beta cell damage in IDDM.