Chronic nitric oxide synthase inhibition and carotid artery distensibility in renal hypertensive rats

The goal of the present study was to examine the viscoelastic properties of the carotid artery in genetically identical rats exposed to similar levels of blood pressure sustained by different mechanisms. Eight-week old male Wistar rats were examined 2 weeks after renal artery clipping (two-kidney, one clip [2K1C] Goldblatt rats, n = 53) or sham operation (n = 49). One half of the 2K1C and sham rats received the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME, 1.48 mmol/L) in their drinking water for 2 weeks after the surgical procedure. Mean blood pressure increased significantly in the 2K1C-water (182 mm Hg), 2K1C-L-NAME (197 mm Hg), and sham-L-NAME (170 mm Hg) rats compared with the sham-water rats (127 mm Hg). Plasma renin activity was not altered by L-NAME but significantly enhanced after renal artery clipping. A significant and similar increase in the cross-sectional area of the carotid artery was observed in L-NAME and vehicle-treated 2K1C rats. L-NAME per se did not modify cross-sectional area in the sham rats. There was a significant upward shift of the distensibility-pressure curve in the L-NAME- and vehicle-treated 2K1C rats compared with the sham-L-NAME rats. L-NAME treatment did not alter the distensibility-pressure curve in the 2K1C rats. These results demonstrate that the mechanisms responsible for artery wall hypertrophy in renovascular hypertension are accompanied by an increase in arterial distensibility that is not dependent on the synthesis of nitric oxide.     

Inhibition of inducible nitric oxide synthase after myocardial ischemia increases coronary flow

BACKGROUND: The role of nitric oxide synthase in myocardial ischemia-reperfusion injury is complex. Our hypothesis was that inducible nitric oxide synthase has a role in the regulation of coronary flow after ischemia. METHODS: Four groups of isolated blood-perfused rabbit hearts underwent sequential periods of perfusion, ischemia, and reperfusion (20, 30, and 20 minutes). Two groups underwent 40 minutes of perfusion. Ischemic groups received saline vehicle, N omega-nitro-L-arginine methyl ester (L-NAME) or the highly specific inducible nitric oxide synthase inhibitor 1400W in low or high doses during reperfusion. Two nonischemic groups were treated with saline vehicle or 1400W during the last 20 minutes of perfusion. Left ventricular developed pressure and coronary flow were measured after each perfusion period. Ventricular levels of myeloperoxidase and cyclic guanosine monophosphate were measured at the end of the second perfusion period. RESULTS: Coronary flow was significantly increased in both 1400W groups versus L-NAME (p < 0.001) and in high-dose 1400W versus control (p < 0.001). Coronary flow was not significantly different between the nonischemic groups. Left ventricular developed pressure was not significantly different among the ischemic groups or between the two nonischemic groups. There were no differences in cyclic guanosine monophosphate levels in any of the ischemic hearts. Myeloperoxidase levels were significantly elevated in L-NAME versus high-dose 1400W, nonischemic 1400W, and nonischemic saline groups (p < 0.02). CONCLUSIONS: Highly selective inhibition of inducible nitric oxide synthase results in increased coronary flow after ischemia but not after continuous perfusion. This occurs with decreased neutrophil accumulation and a trend toward increased contractility without elevation of cyclic guanosine monophosphate levels.     

Overexpressed nitric oxide synthase in portal-hypertensive stomach of rat: a key to increased susceptibility to damage?

BACKGROUND & AIMS: Portal hypertension predisposes gastric mucosa to increased injury. The aim of this study was to determine whether overexpression of constitutive nitric oxide synthase (cNOS) is responsible for increased susceptibility of portal-hypertensive (PHT) gastric mucosa to damage. METHODS: In gastric specimens from PHT and sham-operated rats, cNOS messenger RNA expression was determined by Northern blotting and cNOS protein expression by Western blotting, immunohistochemistry, and enzyme activity assay. Extent of ethanol-induced gastric mucosal necrosis, mucosal blood flow, and gastric NOS activity in PHT and sham-operated rats was determined after administration of N(omega)-nitro-L-arginine methyl ester (L-NAME) or saline. RESULTS: cNOS messenger RNA level, cNOS enzyme activity, and fluorescence signals for cNOS were increased significantly in PHT rats compared with controls. Inhibition of overexpressed cNOS by L-NAME (5 mg/kg) significantly reduced ethanol-induced mucosal necrosis and normalized blood flow in PHT gastric mucosa, whereas this dose of L-NAME significantly increased mucosal necrosis in sham-operated rats. CONCLUSIONS: Portal hypertension activates the cNOS gene with overexpression of cNOS protein in endothelia of gastric mucosal vessels. Excessive NO production by overexpressed cNOS may play an important role in the increased susceptibility of PHT gastric mucosa to damage.     

Salvage angiogenesis induced by adenovirus-mediated gene transfer of vascular endothelial growth factor protects against ischemic vascular occlusion

PURPOSE: Vascular endothelial growth factor (VEGF) is a potent stimulator of angiogenesis, and transgene expression from adenovirus vectors can provide in vivo delivery of proteins. On the basis of this knowledge, we hypothesized that local administration of a replication-deficient adenovirus vector expressing complementary DNA for VEGF (AdVEGF) would induce collateral vessel formation in the setting of ischemia that could protect against subsequent acute vascular occlusion. METHODS: Hindlimb ischemia was induced in Sprague-Dawley rats by means of unilateral ligation of the common iliac artery immediately followed by administration of 4 x 10(9)-plaque-forming units VEGF, the control vector AdNull, or phosphate-buffered saline solution into the iliofemoral adipose tissue and thigh muscles. Untreated rats with common iliac ligation were used as an additional control group. RESULTS: Local VEGF expression was observed for 5 days in AdVEGF-treated rats but not in controls. Three weeks after ligation and vector administration, the ipsilateral femoral artery was ligated for a model of an acute vascular occlusion in the setting of preexisting ischemia. Blood flow to the ischemic hindlimb relative to the contralateral hindlimb evaluated with color microspheres demonstrated significantly increased blood flow in the AdVEGF-treated rats compared with each control group (p < 0.0001). Relative blood flow assessed by means of 99mTc-sestamibi radionuclide scans also demonstrated increased blood flow to the ligated hindlimb of AdVEGF-treated rats compared with each control group (p < 0.002). AdVEGF-treated rats also demonstrated increased vascularity in the ligated limb compared with each control group as assessed by means of angiography (p < 0.0001) and histologic quantification of blood vessels less than 80 microm diameter in local adipose tissue and capillaries per muscle fiber (p < 0.0002). AdVEGF treatment prevented a rise in femoral venous lactate femoral venous concentrations 1 hour after femoral artery ligation in control rats (p < 0.04). CONCLUSIONS: An adenovirus vector expressing VEGF complementary DNA is capable of stimulating an angiogenic response that protects against acute vascular occlusion in the setting of preexisting ischemia, suggesting that in vivo gene transfer of VEGF complementary DNA might be useful in prophylaxis of advancing arterial occlusive disease.     

Inhibition of neuronal (type 1) nitric oxide synthase prevents hyperaemia and hippocampal lesions resulting from kainate-induced seizures

The possible roles for nitric oxide produced by neurons in epileptic conditions have been investigated from two different aspects: microcirculation and delayed damage. Our aim was to determine whether the selective inhibition of neuronal (type 1) nitric oxide synthase by 7-nitroindazole, during seizures induced by systemic kainate, modifies hippocampal blood flow and oxygen supply and influences the subsequent hippocampal damage. Experiments were performed in conscious Wistar rats whose electroencephalogram was recorded. 7-Nitroindazole (25 mg/kg, i.p.) or its vehicle was injected 30 min before kainate administration (10 mg/kg, i.p.) and then twice at 1-h intervals. Kainate triggered typical limbic seizures evolving into status epilepticus, identified by uninterrupted electroencephalographic spike activity. The seizures were stopped by diazepam (5 mg/kg, i.p.) after 1 h of status epilepticus. Three types of experiments were performed in vehicle- and 7-nitroindazole-treated rats. (1) Hippocampal nitric oxide synthase activity was measured under basal conditions, at 1 h after the onset of the status epilepticus and at 24 h after its termination (n = 4-6 per group). (2) Hippocampal blood flow and tissue partial pressure of oxygen were measured simultaneously by mass spectrometry for the whole duration of the experiment, while systemic variables and body temperature were monitored (n = 6 per group). (3) Hippocampal damage was revealed by Cresyl Violet staining and evaluated with a lesion score seven days after status epilepticus (n = 12 per group). Hippocampal nitric oxide synthase activity was not significantly modified during status epilepticus or the following day in vehicle-treated rats. In contrast, it was inhibited by 57% in 7-nitroindazole-treated rats, both in basal conditions and after 1 h of status epilepticus, but was not different from its basal level 24 h later. 7-Nitroindazole significantly decreased basal hippocampal blood flow and tissue partial pressure in oxygen by 30% and 35%, respectively without affecting any systemic or thermal variable. During status epilepticus, 7-nitroindazole significantly reduced the increase in hippocampal blood flow by 70% and prevented any increase in the tissue partial pressure of oxygen. Seven days later, the hippocampal damage in the CA1 and CA3 layers was significantly less in 7-nitroindazole-treated rats than in vehicle-treated rats. These results indicate that the inhibition of neuronal nitric oxide synthase by 7-nitroindazole protects neurons from seizure-induced toxicity despite reducing blood flow and oxygen supply to the hippocampus.     

p53 gene transfer to the injured rat carotid artery decreases neointimal formation

PURPOSE: We studied the effect of adenovirus-mediated p53 gene transfer on the injured rat carotid artery to determine its ability to decrease the formation of neointima. METHODS: In vivo gene transfer was used in isolated segments of balloon-injured rat carotid arteries. Genetically modified adenovirus containing the gene encoding for wild-type p53 (AdWTp53) was applied in three concentrations: 8 x 10(10), 1.6 x 10(10), and 8 x 10(9) pfu/mL. Control rats received either adenovirus null (AdNull), 8 x 10(10) pfu/mL, or Medium-199 solution (vehicle). Expression of p53 was determined 4 days after gene transfer by Western blotting. Neointimal formation was assessed after 14 days by harvesting carotid arteries and determining the intima/media (I/M) ratio based on cross-sectional area measurement. Simultaneously, immunohistochemistry was done to detect the presence of p53 on smooth muscle cell nuclei. RESULTS: P53 expression was confirmed by Western blotting. There was a significant reduction in neointimal formation on all treated animals compared with controls. The highest dose of AdWTp53 (8 x 10(10) pfu/mL) resulted in a near-total arrest of neointimal formation (I/M = 0.09 +/- 0.03, mean +/- SEM) with P <. 0001 versus vehicle (I/M = 2.23 +/- 0.15) or AdNull (I/M = 2.12 +/-. 12). The intermediate dose of AdWTp53 (1.6 x 10(10) pfu/mL) resulted in an I/M value of 1.04 +/- 0.18, with P <.001 versus vehicle and P =.001 versus AdNull. The lowest dose (8 x 10(9) pfu/mL) resulted in an I/M value of 1.12 +/- 0.18, with P <.001 versus vehicle and P <. 002 versus AdNull. The immunohistochemistry was positive for the presence of p53 in rats infected with AdWTp53. CONCLUSIONS: Adenovirus-mediated gene transfer of p53 protein significantly decreases the formation of neointima in the rat carotid injury model. This may represent a potential therapy for restenosis in humans.     

Elements of the art of practice in mental health

This study examined links between impaired nitric oxide production in the sciatic endoneurium, nerve blood flow, and polyol pathway flux, to test the hypothesis that reduced nerve blood flow might be compromised by competition for NADPH between aldose reductase and nitric oxide synthase. Sciatic nerves of streptozotocin-diabetic rats showed reduced laser Doppler flux (by 51% or 63%; both p<0.05)-indicative of reduced nerve blood flow-and reduced motor nerve conduction velocity (17% in two experiments; p<0.05). Acute interruption of nitric oxide production in the sciatic nerves of control rats, via endoneurial injection of N omega-nitro-D-arginine methyl ester (L-NAME), caused a local reduction (of 64%; p<0.001) in nerve Doppler flux. This was reversed by either L-arginine or sodium nitroprusside. The response to L-NAME was greatly reduced in diabetic rats (only 22% reduction; p<0.01), though both L-arginine and SNP caused marked increases in flux. Chronic inhibition of aldose reductase in diabetic rats (with either sorbinil or imirestat at a range of doses) had little effect on resting sciatic nerve Doppler flux, though both inhibitors normalized conduction velocity. Both aldose reductase inhibitors reduced sorbitol pathway intermediates in a dose-related manner. These findings do not support the proposition that aldose reductase inhibitors normalise conduction velocity by mechanisms dependent upon either normalization of endoneurial nitric oxide or nerve blood flow. Instead, a mechanism based upon more direct effects on axon or Schwann cell function is favoured.     

Inhibition of nitric oxide synthesis inhibits rat sleep

Previous findings indicate that nitric oxide (NO) may play a role in the regulation of sleep-wake activity. In rabbits, blocking the production of endogenous NO by a nitric oxide synthase inhibitor, N omega-nitro-L-arginine (L-NAME) suppresses spontaneous sleep and interferes the somnogenic actions of interleukin 1. In the present experiments we extended our earlier work by studying the long-term effects of L-NAME treatment on sleep-wake activity including power spectra analyses of the electroencephalogram (EEG) in rats. Rats implanted with EEG electrodes, brain thermistor, and intracerebroventricular (i.c.v.) guide cannula were injected i.c.v. with vehicle or 0.2, 1, or 5 mg L-NAME at light onset. In separate experiments, rats were injected intraperitoneally (i.p.) with L-NAME three times (50, 50, 100 mg/kg), 12-12 h apart. Both i.c.v. and i.p. injections of L-NAME elicited decreases in time spent in NREMS and REMS. After i.c.v. injection of 5 mg L-NAME the sleep responses were long-lasting; NREMS did not return to baseline even 72 h after injection. EEG delta-wave activity during NREMS (slow wave activity) was also suppressed after 0.2 and 5 mg L-NAME. Brain temperature was slightly increased after the two lower doses of L-NAME, whereas there was a transient decrease in Tbr after 5 mg L-NAME. Acute i.p. injection of 50 mg/kg L-NAME elicited an immediate decrease in NREMS which lasted for approximately 2 h. The second injection of 50 mg/kg L-NAME and the following injection of 100 mg/kg L-NAME induced biphasic decreases in NREMS but not REMS.     

Mechanisms of stroke in sickle cell disease: sickle erythrocytes decrease cerebral blood flow in rats after nitric oxide synthase inhibition

The etiology of stroke in sickle cell disease is unclear, but may involve abnormal red blood cell (RBC) adhesion to the vascular endothelium and altered vasomotor tone regulation. Therefore, we examined both the adhesion of sickle (SS)-RBCs to cerebral microvessels and the effect of SS-RBCs on cerebral blood flow when the nitric oxide (NO) pathway was inhibited. The effect of SS-RBCs was studied in the rat cerebral microcirculation using either a cranial window for direct visualization of infused RBCs or laser Doppler flowmetry (LDF) to measure RBC flow. When fluorescently labeled human RBCs were infused into rats, SS-RBCs had increased adhesion to rat cerebral microvessels compared with control AA-RBCs (P = .01). Next, washed SS-RBCs or AA-RBCs were infused into rats prepared with LDF probes after pretreatment (40 mg/kg intravenously) with the NO synthase inhibitor, N-omega-nitro-L-arginine methyl ester (L-NAME), or the control isomer, D-NAME. In 9 rats treated with systemic L-NAME and SS-RBCs, 5 of 9 experienced a significant decrease in LDF and died within 30 minutes after the RBC infusion (P = .0012). In contrast, all control groups completed the experiment with stable LDF and hemodynamics. Four rats received a localized superfusion of L-NAME (1 mmol/L) through the cranial window followed by infusion of SS-RBCs. Total cessation of flow in all observed cerebral microvessels occurred in 3 of 4 rats within 15 minutes after infusion of SS-RBCs. We conclude that the NO pathway is critical in maintaining cerebral blood flow in the presence of SS-RBCs in this rat model. In addition, the enhanced adhesion of SS-RBCs to rat brain microvessels may contribute to cerebral vaso-occlusion either directly, by disrupting blood flow, or indirectly, by disturbing the vascular endothelium.     

Failure of L-NAME to cause inhibition of nitric oxide synthesis: role of inducible nitric oxide synthase

We addressed the hypothesis that administration of nitric oxide synthase inhibitor, NG -nitro-L-arginine methyl ester (L-NAME) does not result in a sustained suppression of nitric oxide (NO) synthesis, because of a compensatory expression of inducible nitric oxide synthase (iNOS). L-NAME was administered in the drinking water (0.1-1.0 mg/ml) for 7 days to guinea pigs and rats. Nitric oxide synthesis was assessed by [1] ex vivo formation of nitrite in blood vessels and intestine [2] tissue levels of cGMP [3] iNOS gene expression by RT-PCR [4] NADPH diaphorase staining [5] direct assessment of NO release in tissue explants using a microelectrode/electrochemical detection system. Chronic L-NAME administration elevated intestinal cGMP and nitrite levels in guinea pigs (p < 0.05). In rats, intestinal nitrite levels were comparable in control and L-NAME treatment groups, whereas direct assessment of NO release defined a marked increase in the L-NAME group. Chronic L-NAME resulted in an induction of iNOS gene expression in rats and guinea pigs and novel sites of NADPH diaphorase staining in the intestine. We conclude that iNOS expression is responsible for a compensatory increase or normalization of NO synthesis during sustained administration of L-NAME.     

Single-stage repair of aortic arch obstruction and associated intracardiac defects with pulmonary homograft patch aortoplasty

PURPOSE: To investigate the involvement of the cornea during endotoxin-induced uveitis (EIU) in the rat and the effect of Ngamma-nitro-L-arginine methyl ester (L-NAME) as nitric oxide synthase (NOS) inhibitor, administered by iontophoresis. METHODS: EIU was induced in Lewis rats that were killed at 8 and 16 hours after lipopolysaccharide (LPS) injection. The severity of uveitis was evaluated clinically at 16 hours, and nitrite levels were evaluated in the aqueous humor at 8 hours. Corneal thickness was measured, 16 hours after LPS injection, on histologic sections using an image analyzer. Transmission electron microscopy (TEM) was used for fine analysis of the cornea. Transcorneoscleral iontophoresis of L-NAME (100 mM) was performed either at LPS injection or at 1 and 2 hours after LPS injection. RESULTS: At 16 hours after LPS injection, mean corneal thickness was 153.7+/-5.58 microm in the group of rats injected with LPS (n=8) compared with 126.89+/-11.11 microm in the saline-injected rats (n=8) (P < 0.01). TEM showed stromal edema and signs of damage in the endothelial and epithelial layers. In the group of rats treated by three successive iontophoreses of L-NAME (n=8), corneal thickness was 125.24+/-10.36 microm compared with 146.76+/-7.52 microm in the group of rats treated with iontophoresis of saline (n=8), (P=0.015). TEM observation showed a reduction of stromal edema and a normal endothelium. Nitrite levels in the aqueous humor were significantly reduced at 8 hours by L-NAME treatment (P=0.03). No effect on corneal edema was observed after a single iontophoresis of L-NAME at LPS injection (P=0.19). Iontophoresis of saline by itself induced no change in corneal thickness nor in TEM structure analysis compared with normal rats. CONCLUSIONS: Corneal edema is observed during EIU. This edema is significantly reduced by three successive iontophoreses of L-NAME, which partially inhibited the inflammation. A role of nitric oxide in the corneal endothelium functions may explain the antiedematous effect of L-NAME.     

Drinking and blood pressure responses to central injection of L-NAME in conscious rats

The drinking behavior and blood pressure responses to i.c.v. administration of artificial cerebrospinal fluid (aCSF) or NG-nitro-L-arginine methyl ester (L-NAME, 10, 250, or 500 micrograms), an inhibitor of nitric oxide synthase, were examined in conscious rats following either osmotic stimulation (1.0 M NaCl, 15 ml/kg, s.c.) or induction of hemorrhage (0.7 ml/min to a 20% blood volume loss). Water intake increased in all animals. L-NAME at doses of 250 and 500 micrograms, but not 10 micrograms, significantly attenuated water consumption induced by both stimuli. The mean arterial blood pressure (MABP), which increased after osmotic stimulation, was maintained at pressor levels by 250 and 500 micrograms of L-NAME, but decreased progressively and reached basal levels after treatment with aCSF and the lowest dose of L-NAME (i.e., 10 micrograms). Hemorrhage significantly decreased MABP in all rats. The fall in blood pressure associated with hemorrhage returned to control levels in animals treated with 250 and 500 micrograms of L-NAME but not in those treated with aCSF or 10 micrograms of L-NAME. These results indicate that nitric oxide is involved in the regulation of drinking behavior and may play an important role in the central control of blood pressure during osmotic stimulation and hypotensive hemorrhage.     

The occlusal theory further complicated

The aim of the study is to identify nitric oxide synthase (NOS) in the rabbit cornea and further investigate the physiological role of nitric oxide in the rabbit cornea. For histological identification, an immunohistochemical technique using anti-NOS monoclonal antibodies was employed. For the physiological study, we measured the corneal thickness in vivo as an indicator of corneal edema by ultrasonic pachymetry. The measurements were repeated before and after ipsilateral injections of N(G)-nitro-L-arginine methyl ester (L-NAME) or N(G)-nitro-D-arginine methyl ester (D-NAME) or 6-anilino-5,8-quinolinedione (LY-83583) with contralateral injection of vehicle (balanced salt solution) into the anterior chamber of the rabbit. We also monitored intraocular pressure (IOP) by pneumatonometry. Endothelial NOS (eNOS) immunoreactivity was demonstrated both in the corneal epithelium and the endothelium. The corneal thickness significantly increased after L-NAME or LY-83583 without significant rise of IOP, whereas no change was detected after vehicle or D-NAME. These results suggest that NO is spontaneously produced in the corneal endothelium and the NO/cyclic GMP pathway is involved in maintainance of corneal thickness.     

Chronic inhibition of nitric oxide production accelerates neointima formation and impairs endothelial function in hypercholesterolemic rabbits

To determine if endogenous local levels of nitric oxide (NO) modulate atherogenesis, we studied the effect of inhibiting NO with NG-nitro-L-arginine methyl ester (L-NAME) on early neointima formation in cholesterol-fed rabbits. Male rabbits were fed for 5 weeks with a 0.5% cholesterol diet alone or treated in addition during the last 4 weeks with L-NAME (12 mg/kg per day SC) via osmotic minipump. Endothelial cell function was assessed in isolated aortic rings by vascular reactivity and levels of cyclic GMP. In L-NAME-treated rabbits there was inhibition of endothelium-dependent relaxations to acetylcholine and the calcium ionophore A23187 as well as impaired cyclic GMP accumulation in response to acetylcholine. Neointima formation in the ascending thoracic aorta was assessed by determining media and intima cross-sectional areas with computerized image analysis. Compared with rabbits that consumed the cholesterol diet alone, L-NAME-treated rabbits had significant increases in lesion area (0.29 +/- 0.04 versus 0.15 +/- 0.03 mm2) and in lesion/media ratio (0.06 +/- 0.01 versus 0.03 +/- 0.01). Plasma levels of cholesterol and fluorescent lipid peroxide products were unchanged, suggesting no difference in cholesterol metabolism or oxidation. Because arterial blood pressure was not altered by L-NAME treatment, the increased atherogenesis could not be attributed to an increase in blood pressure. These results indicated that local inhibition of NO accelerates early neointima formation possibly because of modulating monocyte recruitment or foam cell lipid accumulation.     

Oxygen radicals and nitric oxide in rat mesenteric ischaemia-reperfusion: modulation by L-arginine and NG-nitro-L-arginine methyl ester

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

Possible role for nitric oxide releasing nerves in the regulation of ocular blood flow in the rat

AIM: To investigate the role of nitrergic nerves in the regulation of ocular blood flow. METHODS: Conscious, lightly restrained rats were treated with either the neuronal nitric oxide synthase inhibitor 7-nitroindazole (7-NI), or the nonselective inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), and ocular blood flow was measured ex vivo from tissue samples, using the fully quantitative [14C]-iodoantipyrine technique. RESULTS: In the peripheral circulation, L-NAME produced an increase in arterial blood pressure (+22%) while 7-NI had no effect. In contrast, both 7-NI and L-NAME produced significant decreases in ocular blood flow (-31% and -59% respectively). The ocular vascular resistance calculated from ocular blood flow and mean arterial blood pressure increased by 29% following 7-NI, but by 130% following L-NAME. CONCLUSIONS: Nitric oxide releasing neurons may play an important contributory role in regulating ocular blood flow.     

The role of EDRF-NO in the regulation of bone blood flow in rats: inhibition with L-NAME

EDRF-NO probably participates-besides the prostaglandins [3, 4]-in local circulatory changes in the bones of female rats with modified level of sex hormones; we could demonstrate it indirectly using methylene blue as a blocking agent [5]. In this paper, we present corresponding results of two experiments with NG-nitro-arginine methyl ester (L-NAME) as a substance blocking the production of endothelium derived relaxing factor, i.e. nitric oxide (EDRF-NO). Circulatory values were estimated by means of 85Sr-microspheres. In experiment A we ascertained whether the duration of L-NAME administration (0.025% in the food) influenced the effect. It could be demonstrated that the effect of one week's, two weeks', or four weeks' administration of L-NAME was the same: 85Sr-microsphere uptake and blood flow throught the tibia of female rats, increased after oophorectomy (OOX, performed four weeks prior to the experiment), was significantly suppressed to the level in sham-operated animals. In the experiment B, L-NAME was administered in the food in concentration of 0.05% for two weeks prior to the experiment. 85Sr-microsphere uptake was decreased significantly after L-NAME in the tibia of sham-operated females, in the tibia and distal femur of OOX animals; no significant changes were found in the diaphysis of femur and in calvaria. Blood flow values were significantly decreased in all bone samples of OOX females and in tibia of sham-operated rats (besides the local reaction also due to the decrease in the cardiac output). In both experiments the cardiac output was decreased and blood pressure elevated after L-NAME. It can be concluded, from the results of both experiments, that the blockade of EDRF-NO production by L-NAME decreases local circulatory values in the bones of female rats-particularly OOX-in a similar way as methylene blue; however, in contrast to methylene blue, L-NAME induces marked increase in the blood pressure and partially decrease in the cardiac output. Thus, as in the case of methylene blue, the effect of L-NAME on the circulation of blood in the rat bones supports the hypothesis of the participation of EDRF-NO in bone blood flow regulations.     

Relationship between nitric oxide and platelet-activating factor in castor-oil induced mucosal injury in the rat duodenum

The modulation of platelet activating factor (PAF) formation in duodenal tissue by nitric oxide (NO) released in response to castor oil was studied in rats pretreated with NG-nitro-L-arginine methyl ester (L-NAME, 6.25-25 mg/kg, i.p.), an inhibitor of NO synthase, NG-nitro-D-arginine methyl ester (D-NAME, 25 mg/kg, i.p.), the inactive enantiomer of L-NAME or isosorbide-5-mononitrate (IMN, 30-90 mg/kg, p.o.), a NO donating compound. Castor oil (2 ml/rat orally) increased PAF production in the rat duodenum 3 h after challenge. L-NAME, but not D-NAME, enhanced the amount of PAF formed by duodenal tissue, while IMN (30-90 mg/kg) counteracted the effects of L-NAME (12.5 mg/kg) and also reduced PAF release in the tissue of rats treated with castor oil. L-NAME 12.5 mg/kg, but not D-NAME, enhanced both macroscopic damage and acid phosphatase release induced by castor oil. These effects were reduced by a PAF antagonist BN 52021 (3-t-Butyl-hexahydro-4, 7b, 11-trihydroxy-8-methyl-9H-1, 7a-epoxymethano-1H, 6aH-cyclopenta [c] furo [2, 3b] furo [3'2':3,4] cyclopenta [1.2-d]furan-5,9,12(4H)trione) 10 and 20 mg/kg i.p. Such findings suggest that endogenous nitric oxide could reduce PAF biosynthesis in castor oil-treated rats.     

Cholinergic receptor-mediated responses in the arteriolar and venous vascular beds of the human forearm

Different antihypertensive treatment regimes were studied in rats during long-term inhibition of nitric oxide synthesis. Male Munich Wistar rats (weight 150-200 g) were put on oral L-nitro-arginine methyl ester (L-NAME, 50 mg/l drinking water) for 12 weeks. The control group (n = 16) received only tap water. Six weeks after starting L-NAME administration rats were divided into 7 groups (n = 13 in each group: group 1, no treatment; group 2, l-arginine 1 g/l drinking water; group 3, doxazosin 30 mg/kg/day; group 4, felodipine 25-30 mg/kg/day; group 5, losartan 40 mg/kg/day; group 6, metoprolol 300-350 mg/kg/day, and group 7, ramipril 1 mg/kg/day. Systolic blood pressure (sBP) was measured in the conscious rat 1, 6, and 12 weeks after study begin. After a treatment period of 6 weeks albuminuria, glomerular filtration rate (GFR) and renal plasma flow (RPF; inulin and p-aminohippuric acid clearance) were analyzed. All rats showed a significant increase in sBP under 6 weeks of L-NAME administration. Control rats remained normotensive during the whole study period. Rats receiving L-NAME without antihypertensive treatment showed a further increase in sBP after 12 weeks. Blood pressure was lowered in all treated animals, except in rats receiving l-arginine. Values for GFR were lowest in the placebo group, the l-arginine group and in rats receiving felodipine (p < 0.05 compared to the control group). RPF was lowest in the placebo group, the l-arginine group, the felodipine group and the ramipril group (p < 0.05 compared to the control group).(ABSTRACT TRUNCATED AT 250 WORDS)     

Complement components and their activation products in pleural fluid

BACKGROUND: This study examined the influences of isoflurane versus halothane anesthesia on basal and agonist-stimulated nitric oxide in the cerebellum of intact rats. Nitric oxide was measured using the hemoglobin-trapping method in an in vivo microdialysis technique. This method uses the stoichiometric reaction of nitric oxide with oxyhemoglobin to produce methemoglobin and nitrate; the change in methemoglobin concentration is measured spectrophotometrically to estimate nitric oxide concentration. METHODS: Male Wistar rats were anesthetized with isoflurane (1.4%) or halothane (1.2%), mechanically ventilated and paralyzed (intravenous pancuronium, 1 mg/kg). Microdialysis probes were implanted into the cerebellum. Bovine oxyhemoglobin dissolved in artificial cerebrospinal fluid was pumped through the probe (2 microl/min) and assayed at 15-min intervals. The glutamatergic agonist, kainic acid (KA, 5 mg/kg, intraarterially), was used to stimulate nitric oxide production. NG-nitro L-arginine methyl ester (L-NAME, 40 mg/kg, intravenously) was used to inhibit nitric oxide synthase. RESULTS: Unstimulated cerebellar nitric oxide concentrations were stable and greater during anesthesia with isoflurane (532+/-31 nM; mean +/- SEM) than with halothane (303+/-23 nM). L-NAME pretreatment reduced nitric oxide concentrations during isoflurane, but not halothane, anesthesia. Infusion of KA increased nitric oxide in both groups; however, the increase in nitric oxide was significantly greater during isoflurane anesthesia. Pretreatment with L-NAME inhibited the response to KA in both groups. CONCLUSIONS: Nitric oxide production in the cerebellum, monitored by microdialysis, was greater during isoflurane anesthesia than during halothane anesthesia. Increased nitric oxide production during isoflurane anesthesia would be expected to impact central neuronal function and cerebral blood flow and vascular resistance.