Coadministration Of L-arginine Research Articles

Luminal calcium in regulation of nitric oxide release and acid secretion in rat stomachs after damage.

We investigated the role of luminal Ca2+ in the regulation of nitric oxide (NO) release and acid secretion in the rat stomach following damage by sodium taurocholate (TC). Under urethane anesthesia, a rat stomach was mounted in an ex vivo chamber, perfused with saline, and transmucosal potential difference (PD), luminal pH, acid secretion, and luminal contents of Ca2+ and NO were measured before and after exposure to 20 mM TC for 30 min, with or without coapplication of EGTA (5 mM) and/or CaCl2 (10 mM). Mucosal exposure to TC caused a reduction in PD and a decrease of acid secretion, with a concomitant increase of NO as well as Ca2+ content in the gastric lumen. The increase of NO release as well as the reduced acid response were attenuated by pretreatment with L-NAME or coapplication of EGTA, and the latter inhibited the luminal increase of Ca2+. The changes caused by L-NAME were antagonized by coadministration of L-arginine, while those induced by EGTA were partially antagonized by coinstillation of CaCl2. Neither treatment tested had any effect on gastric PD responses to TC. These results suggest that: (1) damage in the stomach increases the release of Ca2+ as well as NO in the lumen; (2) acid secretion decreases in response to damage by both an NO- and Ca2+-dependent mechanism; and (3) the increase of luminal Ca2+ is an adaptive response of the stomach to damage and may play an important role in increasing NO production and hence in regulating acid secretion.

The nitric oxide synthesis inhibitor nitro-L-arginine (L-NNA) attenuates nicotine abstinence syndrome in the rat.

Nitric oxide synthesis contributes to opiate tolerance and dependence. Nicotine dependence and abstinence syndrome in the rat appear to involve opiate mechanisms. Therefore, it was postulated that nitric oxide synthase (NOS) activity might be essential for the expression of nicotine abstinence syndrome. Twenty-one rats were rendered dependent by SC infusion of 9 mg/kg per day nicotine tartrate via Alzet osmotic minipump. Rats were pretreated SC with vehicle alone, or with 18 or 30 mg/kg of the NOS inhibitor L-NNA (nitro-L-arginine). Thirty minutes later, rats were challenged by 1 mg/kg of the nicotinic antagonist mecamylamine SC and observed for 30 additional minutes. Rats pretreated with vehicle displayed a total of 68.7+/-8.0 mecamylamine-precipitated abstinence signs (mean+/-SEM), while those receiving 18 or 30 mg/kg L-NNA had 12.7+/-2.0 and 5.1+/-1.7 signs, respectively. All three groups differed significantly from one another according to Dunn's post-hoc procedure. Rats pretreated with L-NNA combined with an excess of the NOS substrate L-arginine had significantly more mecamylamine-precipitated abstinence signs than rats receiving L-NNA combined with D-arginine. Also, D-NNA, which does not selectively bind to NOS, was significantly less effective than L-NNA in preventing mecamylamine-precipitated abstinence syndrome. Additional studies determined the effect of L-NNA on spontaneous nicotine abstinence syndrome. Rats were assessed for abstinence signs at 17 and 20 h after termination of nicotine infusion. They received injections of 9, 18, or 30 mg/kg L-NNA SC or vehicle alone immediately before the 20-h observation; all rats were observed for 30 min. Signs at 20 h (post-injection) as a percentage of signs at 17 h (pre-injection) declined significantly as a function of L-NNA dose. Once again, this effect was attenuated significantly more by co-administration of L-arginine than by D-arginine. The overall pattern of results suggests that nitric oxide synthesis is critical to the expression of nicotine abstinence syndrome.

Gastric mucosal damage induced by compound 48/80: roles of serotonin and nitric oxide.

The roles of nitric oxide (NO) and serotonin (5-HT) in the development of gastric mucosal lesions induced by compound 48/80 (48/80) were investigated in rats. Repeated i.p. administration of 48/80 (1 mg/kg) produced damage in the stomach with severe oedema in the submucosa. The lesions induced by 48/80 were prevented by FPL-52694 (a mast cell stabilizer) and methysergide but not tripelennamine. The lesions were also inhibited by simultaneous administration of N(G)-monomethyl-L-arginine (L-NMMA), and this effect was mimicked by inducible NO synthase (iNOS) inhibitors, such as aminoguanidine or dexamethasone and significantly antagonized by coadministration of L-arginine. The mucosal myeloperoxidase activity, thiobarbituric acid reactants and vascular permeability in the stomach were all increased after 48/80 treatment and the changes were also attenuated by cotreatment with L-NMMA. Repeated s.c. treatment with 5-HT (20 mg/kg) provoked similar gastric lesions, which were also prevented by methysergide and iNOS inhibitors, as well as antioxidative drugs, such as allopurinol (a xanthine oxidase inhibitor) and hydroxyurea (a neutrophil-reducing agent). The Ca2 -independent NO synthase (NOS) activity was increased in the gastric mucosa after administration of 48/80 or 5-HT and this change was inhibited by dexamethasone. These results suggest that: (i) the repeated administration of 48/80 induced inflammatory gastric lesions in the rat stomach, mediated by endogenous 5-HT; (ii) NO/iNOS is involved in the pathogenic mechanism of 48/80-induced gastric lesions, in addition to oxyradical formation; and (iii) the deleterious role of NO in this lesion model can be accounted for by a cytotoxic action of peroxynitrite that is formed in the presence of superoxide radicals.

Nitric oxide modulates gut ischemia-reperfusion-induced P-selectin expression in murine liver.

Reperfusion of ischemic intestine is associated with P-selectin-dependent adhesion of leukocytes in the liver microcirculation. The objective of this study was to define the contribution of nitric oxide (NO) to the enhanced P-selectin expression and increased leukocyte rolling elicited by gut ischemia-reperfusion (I/R). Leukocyte rolling (monitored by intravital microscopy) in the terminal hepatic venules (THV) and P-selectin expression (measured using the dual-radiolabeled monoclonal antibody technique) were determined in mice after 15 min of superior mesenteric artery occlusion and 30 min of reperfusion. After 30 min of reperfusion, P-selectin expression was significantly increased in the liver, intestine, and lung, with a corresponding increase in the number of rolling leukocytes (in THV). The NO synthase inhibitor NG-monomethyl-L-arginine exaggerated the gut I/R-induced increases in both rolling leukocytes and P-selectin expression (in liver and intestine), responses that were not detected with coadministration of L-arginine or in P-selectin-deficient mice. The NO donor diethylenetriamine/NO and L-arginine were both effective in attenuating the gut I/R-induced increases in rolling leukocytes (in THV) and P-selectin expression (in liver, intestine, and lung). These findings indicate that NO modulates gut I/R-induced recruitment of rolling leukocytes in THV via an action on P-selectin expression.

Developmental differences in response of mesenteric artery to acute hypoxia in vitro.

Studies were conducted to determine if the response of in vitro mesenteric artery from 3- and 35-day-old swine to acute hypoxia was age dependent. Isometric tension developed by mesenteric artery rings was measured using a standard myograph apparatus. When the buffer aeration gas was changed from 95% O2-5% CO2 to 95% N2-5% CO2, phenylephrine-precontracted rings from both age groups consistently demonstrated a triphasic response, consisting of, in order, an initial, brief dilation, a sharp contraction, and a sustained loss of tone. The only portion of the triphasic response that was age dependent was the constrictor response, hypoxic vasoconstriction (HVC), which was significantly greater in rings from younger animals. HVC appeared to be mediated by a hypoxia-induced loss of constitutive nitric oxide production. Thus HVC was eliminated by endothelial removal, significantly attenuated by pretreatment with NG-monomethyl-L-arginine (L-NMMA), but not with NG-monomethyl-D-arginine, restored by coadministration of L-arginine, and accentuated by pretreatment with superoxide dismutase. Blockade of endothelin A receptors with BQ-610 or inhibition of cyclooxygenase or lipoxygenase activities with indomethacin or phenidone had no effect on HVC in either group. HVC appeared to be dependent on reduction in PO2, not on reduced ATP secondary to hypoxia, as it did not occur in rings administered 2,4-dinitrophenol, an agent that uncouples oxidative phosphorylation. The magnitude of HVC, which appears to be mediated by hypoxia-induced supression of NO production, is greater in mesenteric artery from 3-day-old swine than from 35-day-old swine.

Cerebroprotective effect of the nitric oxide synthase inhibitors, 1-(2-trifluoromethylphenyl) imidazole and 7-nitro indazole, after transient focal cerebral ischemia in the rat.

The novel neuronal nitric oxide synthase inhibitors, 1-(2-trifluoromethylphenyl)imidazole (TRIM) and 7-nitro indazole (7-NI), were used to investigate the role of nitric oxide in a model of transient focal cerebral ischemia in vivo. In halothane-anesthetized rats, the middle cerebral artery (MCA) was occluded for 2 hours using an intravascular thread and then reperfused for 22 hours before histologic evaluation. TRIM (10, 20, or 50 mg/kg), 7-NI (60 mg/kg), TRIM (50 mg/kg) plus L-arginine (300 mg/kg), or L-arginine (300 mg/kg) alone was administered intraperitoneally, either at 5 or 90 minutes after MCA occlusion. Immediate administration (5 minutes after MCA occlusion) of TRIM produced a dose-related reduction in lesion size, which was reversed with L-arginine coadministration. Similarly, delayed administration of TRIM (90 minutes after MCA occlusion, 50 mg/kg) decreased total lesion volume by 48.4% +/- 13.0% in comparison to a reduction of 39.3% +/- 10.9% when TRIM (50 mg/kg) was administered immediately (5 minutes) after occlusion. 7-NI (60 mg/kg) reduced the total lesion volume by 38.5% +/- 13.7% when administered immediately (5 minutes) after MCA occlusion, but had no effect when administration was delayed (90 minutes). Neither TRIM (50 mg/kg) nor 7-NI (60 mg/kg), administered 5 minutes after MCA occlusion, had any significant effect on mean arterial blood pressure throughout the ischemic period or for up to 10 minutes after reperfusion. These results indicate that immediate or delayed administration of the selective neuronal NOS inhibitor TRIM reduces the lesion volume after transient MCA occlusion. In contrast, only immediate administration of 7-NI reduces lesion volume.

Pressure and flow characteristics of terminal mesenteric arteries in postnatal intestine.

The responses of buffer-perfused terminal mesenteric arteries from 3- and 35-day-old swine to manipulation of intravascular pressure and flow rate were determined. Under in vivo conditions, these vessels demonstrated age-dependent differences in resting diameter (182 vs. 301 microns in 3- vs. 35-day-old swine). A proximal-to-distal pressure gradient was present in vessels from both age groups (delta 13 vs. delta 16 mmHg in 3- vs. 35-day-old swine), suggesting their functional role as resistance vessels. Vessels were mounted within an in vitro perfusion apparatus that allowed independent regulation of inflow and outflow pressure. Vessels from both age groups demonstrated the development of active tone in response to an incremental rise in pressure, applied in the absence of flow. However, myogenic vasoconstriction was only observed in younger arterioles. Similarly, both groups demonstrated dilation in response to a flow stimulus generated in the absence of a net change in intravascular pressure, although the magnitude of this response was significantly greater in younger vessels (+27 vs. +7% in 3- vs. 35-day-old swine). The dilatory response to flow was eliminated by NG-monomethyl-L-arginine (10(-4)M) but restored by coadministration of L-arginine (10(-3)M). Myogenic vasoconstriction was overridden by flow-mediated dilation in terminal mesenteric arteries from 3- but not 35-day-old swine after concomitant application of pressure and flow stimuli. We conclude that the hemodynamic characteristics of terminal mesenteric arteries are age dependent in postnatal swine.

Role of NO in the O2 and CO2 responsiveness of cerebral and ocular circulation in humans.

It is well known that changes in PCO2 or PO2 strongly influence cerebral and ocular blood flow. However, the mediators of these changes have not yet been completely identified. There is evidence from animal studies that NO may play a role in hypercapnia-induced vasodilation and that NO synthase inhibition modulates the response to hyperoxia in the choroid. Hence we have studied the effect of NO synthase inhibition by NG-monomethyl-L-arginine (L-NMMA, 3 mg/kg over 5 min as a bolus followed by a continuous infusion of 30 micrograms.kg-1.min-1) on the changes of cerebral and ocular hemodynamic parameters elicited by hypercapnia and hyperoxia in healthy young subjects. Mean flow velocities in the middle cerebral artery and the ophthalmic artery were measured with Doppler ultrasound, and ocular fundus pulsation amplitude, which estimates pulsatile choroidal blood flow, was measured with laser interferometry Administration of L-NMMA reduced ocular fundus pulsation. (-19%, P < 0.005) but only slightly reduced mean flow velocities in the larger arteries. Hypercapnia (PCO2 = 48 mmHg) significantly increased mean flow velocities in the middle cerebral artery (+26%, P < 0.01) and fundus pulsation amplitude (+16%, P < 0.005) but did not change mean flow velocity in the ophthalmic artery. The response to hypercapnia in the middle cerebral artery (P < 0.05) and in the choroid (P < 0.05) was significantly blunted by L-NMMA. On the contrary, L-NMMA did not affect hyperoxia-induced (PO2 = 530 mmHg) hemodynamic changes. The hemodynamic effects of L-NMMA (at baseline and during hypercapnia) were reversed by coadministration of L-arginine. The present study supports the concept that NO has a role in hypercapnia induced vasodilation in humans.

Role of nitric oxide in gut ischemia-reperfusion-induced hepatic microvascular dysfunction.

The overall objective of this study was to assess the contribution of an altered bioavailability of nitric oxide (NO) to the leukocyte adhesion and hypoxic stress elicited in the liver by gut ischemia-reperfusion (I/R). The accumulation of leukocytes, number of nonperfused sinusoids (NPS), and NADH autofluorescence were monitored (by intravital microscopy) in mouse liver after 15 min of superior mesenteric artery occlusion and 60 min of reperfusion. Leukostasis, NPS, and NADH autofluorescence (indicating hypoxia) were all increased in the liver at 60 min after gut I/R. The NO synthase inhibitor NG-monomethyl-L-arginine (L-NMMA) exaggerated the liver leukostasis elicited by gut I/R, responses that were prevented by coadministration of L-arginine. The NO donor diethylenetriamine-NO (DETA-NO) and L-arginine were both effective in attenuating the gut I/R-induced leukostasis and increased NADH autofluorescence, whereas neither DETA nor D-arginine exerted a protective action. These findings indicate that NO is an important determinant of the liver leukostasis, impaired sinusoidal perfusion, and tissue hypoxia elicited by gut I/R.

Involvement of nitric oxide in 2-deoxy-D-glucose-induced hyperphagia in rats.

The effects of a nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) on 2-deoxy-D-glucose (2-DG)-induced hyperphagia were investigated in rats. L-NAME dose-dependently inhibited 2-DG-induced eating in non-food-deprived rats, although the inactive isomer D-NAME on 2-DG-induced hyperphagia were inhibited by co-administration of L-arginine. The neuronal NO synthase inhibitor 7-nitroindazole also inhibited 2-DG-induced hyperphagia. These results suggest that 2-DG-induced hyperphagia is linked with NO and that brain NO may participate in this hyperphagic model.

Role of nitric oxide in pathogenesis of gastric mucosal damage induced by compound [formula omitted] in rats

We examined the effects of various nitric oxide synthase (NOS) inhibitors on development of gastric lesions induced by compound 48 80 ( 48 80 ) in rats and investigated the roles of NO and inducible NOS (iNOS) in inflammatory gastric responses. Animals were given 48 80 (1 mg/kg, ip) once daily for 4 days, and the stomachs were examined for lesions 24 h after the final administration. NOS inhbitors such as L-NAME, L-NMMA, aminoguanidine or dexamethasone were administered for 4 days during 48 80 treatment. The repeated administration of 48 80 caused damage in the stomach with severe edema in the submucosa. These lesions induced by 48 80 were dose-dependently prevented by concurrent administration of L-NAME. The protective effect of L-NAME on 48 80 - induced gastric lesions was mimicked by L-NMMA, aminoguanidine as well as dexamethasone, and significantly antagonized by co-administration of L-arginine but not by D-arginine. Acid secretion was slightly decreased after 48 80 treatment, but was significantly augmented by the combined administration of L-NAME with 48 80 . The mucosal MPO activity, TBA reactants and vascular permeability in the stomach were all increased after 48 80 treatment, but these changes were also significantly mitigated by co-administration of L-NAME. The Ca 2+-independent NOS activity in the mucosa was increased four times during 48 80 treatment, and this change was also inhibited by dexamethasone. These results suggest that: 1) the repeated administration of 48 80 induced inflammatory gastric lesions in the rat stomach; 2) the pathogenic mechanism of these lesions involves endogenous NO produced by iNOS, in addition to oxyradical formation; and 3) the deleterious role of NO during 48 80 treatment may be accounted for by a cytotoxic action of peroxynitrite, which is formed in the presence of NO and superoxide radicals.

Nitric oxide, prostaglandin, and sensory neurons in gastric mucosal blood flow response during acid secretion in rats

1. 1. The mechanism underlying the increase of gastric mucosal blood flow (GMBF) during acid secretion induced by pentagastrin was investigated in anesthetized rats, in relation to nitric oxide (NO), prostaglandin (PG), and sensory neurons. 2. 2. An intravenous infusion of pentagastrin at 60 μg/kg/h (submaximal dose) produced an increase of acid secretion and GMBF as determined by laser Doppler flowmetry, and the GMBF response was totally attenuated when the acid secretion was inhibited by omeprazole or when the luminal H + was removed by mucosal perfusion with glycine (200 mM). 3. 3. Prior administration of N G-nitro-L-arginine methyl ester (L-NAME, 5 mg/kg, IV), a NO synthase inhibitor, significantly mitigated the GMBF response to pentagastrin, without any influence on acid secretion, and this effect was antagonized by coadministration of L-arginine (500 mg/kg IP). 4. 4. The increase of GMBF during pentagastrin infusion also was significantly mitigated by indomethacin (5 mg/kg, SC) or sensory deafferentation following capsaicin pretreatment, had no effect on the acid secretion, and was totally inhibited by the combined treatments with indomethacin plus L-NAME in addition to sensory deafferentation. 5. 5. Pentagastrin infusion for 8 hr did not by itself cause any macroscopic damage in the stomach, but additional treatments with L-NAME, and indomethacin plus sensory deafferentation provoked severe lesions in the gastric mucosa. 6. 6. These results suggest that the increase of GMBF induced by submaximal dose of pentagastrin totally depends on luminal H +. This process seems to be mediated by endogenous NO and PGs, as well as capsaicin-sensitive sensory neurons, and to play a pivotal role in maintaining mucosal integrity during acid secretion.

Inhibition of nitric oxide synthesis accelerates the recovery of polysynaptic reflex potentials after transient spinal cord ischemia in cats.

Nitric Oxide (NO) has been implicated as a mediator of neuronal injury in vascular stroke. On the other hand, NO is suggested to play a neuroprotective role by increasing blood flow during cerebral ischemia. In order to evaluate the role of NO in the spinal cord ischemia, effects of nitric oxide synthase (NOS) inhibition on the recovery of reflex potentials after a transient spinal cord ischemia were examined in urethane-chloralose anesthetized spinal cats. Spinal cord ischemia was produced by occlusion of the thoracic aorta and the both internal mammary arteries for 10 min. Regional blood flow (RBF) in the spinal cord was continuously measured with a laser-Doppler flow meter. The monosynaptic (MSR) and polysynaptic reflex (PSR) potentials elicited by electrical stimulation of the tibial nerve, were recorded from the L7 or S1 ventral root. The recovery process of spinal reflex potentials was reproducible when the oclusion was repeated twice at an interval of 120 min. Pretreatment with N(G)-monomethyl-L-arginine (L-NMMA, 10 mg/kg), a NOS inhibitor significantly accelerated the recovery of PSR potentials after spinal cord ischemia. The accelerating effect of L-NMMA on the recovery of PSR potentials was abolished by co-administration of L-arginine (1 mg/kg/min) but not by that of D-arginine (1 mg/kg/min). L-NMMA failed to improve RBF in the spinal cord during ischemia and reperfusion. Nitroprusside (10 microg/kg/min), a NO donor, retarded the recovery of PSR potentials after spinal cord ischemia. These results suggest that NO production has a significant influence on the functional recovery after transient spinal cord ischemia.

Nitric oxide, histamine, and sensory nerves in the acid secretory response in rat stomach after damage.

The stomach normally responds to mucosa-damaging agents by decreasing acid secretion, but this acid response turn from "inhibition" into "stimulation" when the production of nitric oxide (NO) is inhibited by NG-nitro-L-arginine methyl ester (L-NAME). We investigated the mechanism underlying stimulation of acid secretion in the stomach after damage with taurocholate (TC) in the presence of L-NAME. A rat stomach was mounted in an ex vivo chamber and perfused with saline, and the potential difference (PD), luminal pH, and acid secretion were measured before and after application of 20 mM TC for 30 min. Exposure of the stomach to TC caused a reduction in PD, an increase in luminal pH, and a decrease in acid secretion. Pretreatment with L-NAME did not affect basal acid secretion but significantly increased secretion after damage with TC, without any effect on PD. This effect of L-NAME was antagonized by co-administration of L-arginine but not D-arginine. The luminal appearance of NO was also increased after exposure of the stomach to TC, a phenomenon completely blocked by L-NAME, or when EGTA was applied together with TC. The enhanced acid secretory response in the presence of L-NAME was inhibited by prior administration of cimetidine, FPL-52694 (a mast cell stabilizer), spantide (a substance P antagonist), or by chemical ablation of capsaicin-sensitive sensory neurons. Mucosal exposure to TC increased histamine output in the lumen and decreased the number of mucosal mast cells in the stomach. These changes were prevented by FPL-52694 or sensory neuronal ablation. These results suggest that (a) damage in the stomach may activate acid stimulation in addition to an NO-dependent inhibitory mechanism but that the latter effect overcomes the former, resulting in a decrease in acid secretion, (b) acid stimulation in the damaged stomach may be mediated by histamine released from the mucosal mast cells, a process that may interact with capsaicin-sensitive sensory nerves, and (c) L-NAME unmasks the acid stimulatory response by suppressing the inhibitory mechanism.

CIRCULATORY FAILURE INDUCED BY 35 GHz MICROWAVE HEATING

Sustained exposure to radiofrequency radiation of millimeter wave (MMW) length produces hyperthermia and subsequent circulatory failure. This study sought to determine whether this phenomenon is altered by chronic pretreatment with the nitric oxide (NO) synthesis inhibitor N omega-nitro-L-arginine methyl ester (L-NAME). Rats drank either 1) water, 2) water + L-NAME, or 3) water + L-NAME + L-arginine (at 20 and 50 times the dose of L-NAME) for 14 days. Ketamine-anesthetized rats were exposed to MMW until mean arterial blood pressure (MAP) fell to 75 mmHg, at which point MMW exposure was discontinued. MAP initially increased during exposure in all groups; the pressor response in L-NAME-treated rats was greater than that in water-drinking rats. Subsequently, MAP fell in all groups. The MMW exposure time required to reach MAP = 75 mmHg was significantly reduced in L-NAME-treated rats, although survival times (post-MMW) of L-NAME-treated and control rats were not statistically different. Coadministration of L-arginine abolished the enhanced pressor response produced by L-NAME, but did not completely reverse the shortened MMW exposure time in L-NAME-treated rats. Thus, chronic NO synthesis inhibition with L-NAME reduces the ability of rats to withstand 35 GHz microwave heating, suggesting that NO does not mediate the hypotension produced by this form of hyperthermia.

Endogenous nitric oxide modifies antigen-induced microvascular leakage in sensitized guinea pig airways

To examine the role of endogenous nitric oxide in allergic airway inflammation, we investigated the effect of a nitric oxide synthase inhibitor, Nω-nitro- l-arginine methyl ester ( l-NAME), on antigen-induced airway microvascular leakage in actively sensitized guinea pigs by using Evans blue dye. Three weeks after sensitization with ovalbumin (10 μg), the tracheas were cannulated, and lungs were artificially ventilated. Animals were pretreated with atropine and propranolol (both 1 mg/kg, intravenously) to avoid neural modification. Ovalbumin inhalation (3 mg/ml, 1 minute) challenge caused significant microvascular leakage in all airway portions, which was significantly suppressed in a dose-dependent manner by pretreatment with intravenous injection of l--NAME (1 and 10 mg/kg) but not with the inactive enantiomer d-NAME (10 mg/kg). This inhibition by l-NAME was significantly reversed by co-administration of l-arginine (100 mg/kg, intravenously). Pretreatment with a vasoconstrictor, phenylephrine (20 μg/kg, intravenously), had no inhibitory effects on antigen-induced airway microvascular leakage despite increasing systemic blood pressure. Inhalation of representative mast cell–derived mediators, histamine (2 mg/ml, 1 minute) or leukotriene D 4 (5 μg/ml, 1 minute), produced significant microvascular leakage in all airways. l-NAME (10 mg/kg, intravenously) partially but significantly inhibited leukotriene D 4–induced leakage, whereas histamine-induced leakage was not affected. These results suggest that endogenous nitric oxide acts to increase airway microvascular leakage after airway allergic reaction. (J A LLERGY C LIN I MMUNOL 1996;98:144-51.)

Stimulation of acid secretion in rat stomach following exposure to taurocholate in the presence of the nitric oxide synthase inhibitor

1. 1. The role of nitric oxide (NO) in the acid secretory response of the rat stomach following damage was investigated. A rat stomach was mounted in an ex-vivo chamber, perfused with saline, and the potential difference (PD), luminal pH, acid and HCO 3 - responses were measured before and after the mucosal exposure to 20 mM taurocholate (TC) for 30 min, with or without pretreatment with N G-nitro- L-arginine methyl ester ( L-NAME). 2. 2. Exposure of the stomach to TC caused a reduction of PD, a decrease of acid secretion and an increase in luminal HCO. Pretreatment with L-NAME did not affect such PD and HCO 3 - responses, but completely attenuated the decreased acid secretory response and rather enhanced this secretion. 3. 3. These effects of L-NAME were significantly antagonized by the co-administration of L-arginine but not D-arginine. The enhanced acid secretory response in the presence of L-NAME was significantly inhibited by prior administration of cimetidine or FPL-52694 (a mast-cell stabilizer). 4. 4. The mucosal exposure to TC significantly decreased the number of mucosal mast cells and increased the luminal histamine output. 5. 5. Damage in the stomach may activate the histamine-dependent acid stimulatory pathway in addition to the NO-dependent inhibitory mechanism, although the latter effect overcomes the former, resulting in a decrease of acid secretion. L-NAME unmasks the stimulation of acid secretion by suppressing the inhibitory pathway.

Bioactive 6-Nitronorepinephrine Identified in Mammalian Brain

Norepinephrine (NE) (von Euler, U. S. (1972) in Catecholamines (Blaschko, H., and Muscholl, E., eds.) pp. 186-230, Springer-Verlag, Berlin) and nitric oxide (NO.) function as neurotransmitters in the nervous system. We have shown that NE levels in the rat hypothalamic paraventricular nucleus (Shintani, F., Kato, R., Kinoshita, N., Kanba, S., Asai, M., and Nakaki, T.(1995) Proceedings of the Satellite Symposium, 4th IBRO World Congress on Neuroscience, Otsu, 1995) diminish in the presence of NO.. This observation prompted us to explore the possibility of an in vivo interaction between NE and NO. or NO.-related molecules. In fact, nitration of NE has been shown to occur in vitro (d'Ischia, M., and Costantini, C. (1995) Bioorg. Med. Chem. 3, 923-927). We now report the identification of 6-nitronorepinephrine in the mammalian brain. Amounts of 6-nitronorepinephrine in the rat brain were attenuated by intraperitoneal administration of an inhibitor of nitric oxide synthase, NG-nitro-L-arginine methyl ester (L-NAME). This was reversed by coadministration of L-arginine, suggesting that nitric oxide synthase participated in the formation of 6-nitronorepinephrine. Moreover, we found that 6-nitronorepinephrine inhibits the activity of catechol O-methyltransferase, as well as NE transport into rat synaptosomes. A rat brain microdialysis experiment showed that perfusion of 6-nitronorepinephrine into the rat paraventricular nucleus significantly elevated NE while decreasing 3-methoxy-4-hydroxyphenylglycol and that L-NAME administered intraperitoneally decreased NE and increased 3-methoxy-4-hydroxyphenylglycol. These observations suggest that 6-nitronorepinephrine generated in nuclei containing both adrenergic and nitrergic neurons inhibits NE inactivation. We propose that 6-nitronorepinephrine is a potential signal molecule linking the actions of NE and NO..

Effect of L-arginine on myoglobin-induced acute renal failure in the rabbit.

Because myoglobin is a potent inhibitor of nitric oxide (NO), we tested whether myoglobin infusion results in renal vasoconstriction and dysfunction, on which L-arginine, a source of NO, has a protective effect in sedated, nondehydrated, and nonacidotic rabbits. The infusion of myoglobin (375 mg/kg) resulted in a decrease in renal blood flow, an increase in renal vascular resistance, and a decrease in creatine clearance associated with a decrease in urinary excretory rate of nitrite/nitrate and guanosine 3',5'-cyclic monophosphate (cGMP). These values 1-2 h after the infusion were significantly different from baseline levels. Co-administration of L-arginine (150 mg/kg bolus followed by 150 mg.kg(-1).min(-1) reversed these changes significantly with attenuation of urinary excretory rate of nitrite/nitrate and cGMP. This study suggests that the myoglobin-induced renal vasoconstriction and dysfunction and protective effect of L-arginine on these outcomes could be mediated through the NO system.

Aminoguanidine ameliorates and L-arginine worsens brain damage from intraluminal middle cerebral artery occlusion.

We studied whether the inducible nitric oxide synthase (iNOS) inhibitor aminoguanidine reduces focal cerebral ischemic damage in a relatively noninvasive stroke model in which the rat middle cerebral artery (MCA) is occluded using an intravascular filament. In rats anesthetized with halothane, a nylon filament was advanced into the internal carotid artery until its tip occluded the origin of the MCA. The filament was left in place for 2 hours and then withdrawn. Twenty-four hours later, rats received intraperitoneal injections of aminoguanidine (100 mg/kg BID; n = 7), aminoguanidine+L-arginine (300 mg/kg QID; n = 7), L-arginine alone (n = 6), D-arginine alone (n = 6), or vehicle (n = 10). Drugs were administered for 3 consecutive days. Infarct volume was determined by image analysis in thionin-stained brain sections 4 days after ischemia. iNOS mRNA was detected with the use of reverse transcription polymerase chain reaction. Cerebral ischemia led to iNOS mRNA expression in the affected brain 48 hours after induction of ischemia. Administration of aminoguanidine reduced neocortical infarct volume by 26% (P < .05 versus vehicle, ANOVA and Tukey's test), a reduction that was antagonized by coadministration of L-arginine (P > .05 versus vehicle). Administration of L-arginine alone, but not D-arginine, enlarged the infarct by 29% (P < .05). Aminoguanidine or L-arginine did not influence the increase in water content in the postischemic brain, indicating that the effect on infarct volume is not related to modulation of ischemic edema. These results demonstrate that cerebral ischemia is also associated with iNOS expression in a minimally invasive model of transient MCA occlusion and that iNOS inhibition reduces focal ischemic damage. The findings support the hypothesis that nitric oxide produced by iNOS contributes to ischemic brain damage and that inhibition of iNOS may be a valuable tool in the management of cerebral ischemia.