nitroarginine and Ischemic-Attack--Transient

Both nitric oxide synthase (NOS) inhibitors and free radical scavengers have been shown to protect brain tissue in ischemia-reperfusion injury. Nitric oxide and superoxide anion act via distinct mechanisms and react together to form the highly deleterious peroxynitrite. Therefore the authors examined the effects and the interaction between the NOS inhibitor, NG nitro-L-arginine (LNA) and the antioxidant/superoxide scavenger, di-tert-butyl-hydroxybenzoic acid (DtBHB) in the rat submitted to 2 hours of middle cerebral artery occlusion. Posttreatment was initiated 4 hours after the onset of ischemia and infarct volume was measured at 48 hours. The dose-related effect of LNA resulted in a bell-shaped curve: 15, 56, 65, and 33% reduction of total infarct for 0.03, 0.1, 0.3, and 1 mg/kg (intravenously [IV]) respectively and 11% increase in infarct volume for 3 mg/kg (IV). Whereas DtBHB (20 mg/kg; intraperitoneally [IP]) was ineffective, the dose of 60 mg/kg produced 65% protection in infarct volume. The combination of a subthreshold dose of LNA (0.03 mg/kg; IV) and DtBHB (20 mg/kg; IP) resulted in significant reduction (49%) in infarct volume. These results show that LNA and DtBHB act synergistically to provide a consistent neuroprotection against ischemic injury when administered 4 hours after ischemia. This suggests that nitric oxide and free radicals are involved and interact in synergy in ischemia-reperfusion injury.

Topics: Animals; Antioxidants; Cerebral Infarction; Drug Administration Schedule; Drug Synergism; Enzyme Inhibitors; Ischemic Attack, Transient; Male; Neuroprotective Agents; Nitric Oxide Synthase; Nitroarginine; Parabens; Rats; Rats, Sprague-Dawley

Free radicals have been suggested to be largely involved in the genesis of ischemic brain damage, as shown in the protective effects of alpha-phenyl-N-tert-butyl nitrone (PBN), a spin trapping agent, against ischemic cerebral injury. In the present study, the effects of PBN as well as MCI-186, a newly-developed free radical scavenger, and oxypurinol, an inhibitor of xanthine oxidase, were evaluated in a rat transient middle cerebral aretery (MCA) occlusion model to clarify the possible role of free radicals in the reperfusion injury of brain. The volume of cerebral infarction, induced by 2-h occlusion and subsequent 2-h reperfusion of MCA in Fisher-344 rats, was evaluated. The administration of PBN (100 mg/kg) and MCI-186 (100 mg/kg) just before reperfusion of MCA significantly reduced the infarction volume. In contrast, oxypurinol (100 mg/kg) failed to show any preventive effect on the infarction. These results suggest that free radical formation is involved in the cerebral damage induced by ischemia-reperfusion of MCA, and that hydroxyl radical is responsible for the reperfusion injury after transient focal brain ischemia. It is also suggested that xanthine oxidase is not a major source of free radicals.

Topics: Animals; Antipyrine; Brain; Caudate Nucleus; Cerebral Infarction; Cyclic N-Oxides; Disease Models, Animal; Edaravone; Free Radical Scavengers; Free Radicals; Hippocampus; Ischemic Attack, Transient; Male; Nitroarginine; Nitrogen Oxides; Putamen; Rats; Rats, Inbred F344; Rats, Wistar; Reperfusion Injury; Spin Labels; Superior Colliculi

After transient cerebral ischemia in fetal sheep, delayed disruptions in cerebral energetics are represented by a delayed increase in cortical impedance, a progressive decrease in the concentration of oxidized cytochrome oxidase as measured by near-infrared spectroscopy, and cortical seizures. Because the production of nitric oxide (NO), a potent mediator of neuronal death, is increased during this phase, the present study investigated whether inhibition of NO synthesis could ameliorate the delayed disruption in cerebral energetics. Eleven late gestation fetal sheep were subjected to 30 min of transient cerebral ischemia in utero. Two hours later, the treatment group (n = 5) received a continuous infusion of N(G)-nitro-L-arginine, a competitive inhibitor of NO synthase, whereas the control group (n = 6) received PBS. Changes in concentration of oxidized cytochrome oxidase, cortical impedance, and electrocortical activity were observed for 3 d. A delayed increase in cortical impedance of similar magnitude and duration commenced at 14+/-4 h in the control and at 15+/-3 h in the treatment groups. The progressive decrease in oxidized cytochrome oxidase signal, by -2.2+/-0.2 micromol/L in the control and -2.0+/-0.4 micromol/L in the treatment group at 72 h postischemia, was similar in both groups. In both groups, delayed cortical seizures were indicated by intense low-frequency electrocortical activity. In the treatment group, duration of cortical seizures was increased and the intensity of the final electrocortical activity was more depressed (-19+/-1 dB versus -10+/-2 dB). The results indicate that after cerebral ischemia in fetal sheep, NO synthase inhibition does not ameliorate the delayed disruptions in cerebral energetics. However, the effect of NO synthase inhibition on delayed cortical seizures may improve our understanding of the role of NO during this phase.

Topics: Animals; Brain; Electroencephalography; Electron Transport Complex IV; Fetus; Gestational Age; Infusions, Intravenous; Ischemic Attack, Transient; Nitric Oxide Synthase; Nitroarginine; Seizures; Sheep; Umbilical Veins

The effects of agents which affect the action of nitric oxide (NO) were studied intracellularly on the ischemia-induced changes in membrane potential of single CA1 pyramidal neurons of the rat hippocampal slice preparations. The N-methyl-D-aspartate (NMDA) receptor antagonists, (+/-)-2-amino-5-phosphonopentanoic acid (AP5, 250 microM) or Co2 (2 mM) restored the membrane potential in more than 80% of the neurons. In about 60% of the neurons, the membrane potential was partially recovered as a result of exposure to the NO synthase inhibitor, NG-nitro-L-arginine (100 microM). The NO scavengers, carboxy-2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO, 300 microM) and hemoglobin (10 microM) restored the membrane potential in all neurons examined. Superoxide dismutase (50 U/ml) protected about 75% of the neurons from irreversible membrane dysfunction. It is concluded that the release of NO induced by experimental ischemia may result in the irreversible membrane dysfunction, and that a NO scavenger, carboxy-PTIO, prevents the ischemic changes in membrane potential. With respect to ischemic brain damage, the neuroprotection provided by carboxy-PTIO may have clinical relevance in the management of a variety of neurological conditions.

Topics: 2-Amino-5-phosphonovalerate; Animals; Benzoates; Cell Membrane; Cobalt; Glucose; Hemoglobins; Hippocampus; Hypoxia; Imidazoles; In Vitro Techniques; Ischemic Attack, Transient; Male; Membrane Potentials; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Pyramidal Cells; Rats; Rats, Wistar; Reaction Time; Receptors, N-Methyl-D-Aspartate; Superoxide Dismutase

We investigated the post-ischemic change in [3H]L-N(G)-nitroarginine binding as a marker of nitric oxide (NO) synthase in the animal brain after transient global ischemia or transient focal ischemia. Transient global ischemia in gerbils was induced for 10 min followed by 1 h to 7 days of recirculation. Transient focal ischemia in rats was induced for 45 min followed by 3 days of recirculation. Following transient global ischemia, [3H]L-N(G)-nitroarginine binding showed a significant increase in the striatum (17-18%) and hippocampal CA1 sector (24%) at 48 and 24 h after recirculation, respectively. The hippocampal CA3 sector also showed a significant elevation (32-40%) in [3H]L-N(G)-nitroarginine binding at 24 and 48 h after global ischemia. Furthermore, the dentate gyrus showed a significant increase (30-32%) in [3H]L-N(G)-nitroarginine binding at 5, 24 and 48 h after global ischemia. Thereafter, a significant reduction in [3H]L-N(G)-nitroarginine binding was observed only in the dentate gyrus 7 days after recirculation. In contrast, [3H]L-N(G)-nitroarginine binding was unchanged in the thalamus throughout the recirculation periods. Histological analysis revealed that transient global ischemia caused severe damage or cellular damage in the striatum and the hippocampal CA1 sector. The hippocampal CA3 sector and thalamus were mildly damaged, whereas the dentate gyrus was morphologically intact. Following transient focal ischemia, a marked elevation (50-52%) in [3H]L-N(G)-nitroarginine binding was found in the regions of the ipsilateral striatum in which severe infarction occurred. Our findings suggest that [3H]L-N(G)-nitroarginine binding increases in the striatum and hippocampus after transient global ischemia or transient focal ischemia. This increase in [3H]L-N(G)-nitroarginine binding may play a pivotal role not only in the pathogenesis of ischemic brain damage, but also in the restoration of injury areas after cerebral ischemia.

Topics: Animals; Autoradiography; Brain; Gerbillinae; Ischemic Attack, Transient; Male; Nitric Oxide Synthase; Nitroarginine; Radionuclide Imaging; Radiopharmaceuticals; Rats; Rats, Wistar; Tritium

By observing the ultrastructural intracellular Ca2+ distribution with Ca(2+)-oxalate-pyroantimonate method, we examined whether the protective mechanism of the nitric oxide (NO) synthase inhibitor, N omega-nitro-L-arginine (LNNA), involves change of the intracellular Ca2+ movement in delayed neuronal death (DND) in gerbil hippocampal CA1 neurons following 5-min forebrain ischemia. In the group intraventricularly administered 5.0 mg/ml LNNA, 15 min after reperfusion the intracellular Ca2+ deposits and the mitochondrial Ca2+ uptake index increased to levels similar to those in the control group administered only artificial cerebro-spinal fluid, but by 180 min after reperfusion they had returned to the preischemic level. By 15 min after reperfusion Ca2+ deposits in the endoplasmic reticulum (ER) had almost disappeared in both groups, but at 180 min of reperfusion, the ER in only the LNNA group showed Ca2+ deposits. It is suggested that the neuronal toxicity of NO involves the dysfunction of the intracellular Ca2+ transport system including the mitochondria and ER.

Topics: Animals; Calcium; Endoplasmic Reticulum; Enzyme Inhibitors; Gerbillinae; Injections, Intraventricular; Intracellular Membranes; Ischemic Attack, Transient; Male; Mitochondria; Neuroprotective Agents; Nitric Oxide Synthase; Nitroarginine; Reperfusion

We investigated the density and distribution of nitric oxide synthase (NOS) binding by quantitative autoradiography using [3H]L-NG-nitroarginine ([3H]L-NNA) after transient focal ischemia or intrastriatal injection of N-methyl-D-aspartate (NMDA) in wild-type (SV-129 and C57black/6) and type I (neuronal) and type III (endothelial) NOS-deficient mice. The middle cerebral artery (MCA) was occluded by an intraluminal filament for 3 h followed by 10 min to 7 days of reperfusion. Specific [3H]L-NNA binding, observed in the wild-type and type III mutant mouse at baseline, increased by 50-250% in the MCA territory during ischemia and the first 3 h of reperfusion. The density of binding sites (Bmax), but not the dissociation constant (Kd), increased significantly during the ischemic period as did type I NOS mRNA as detected by quantitative reverse transcription polymerase chain reaction. [3H]L-NNA binding after intrastriatal NMDA injection also increased by 20-230%. In the type I NOS-deficient mouse, [3H]L-NNA binding was low and only a very small increase was observed after ischemia or excitotoxicity. Under conditions of this study, [3H]L-NNA did not bind to type II NOS as there was no difference in the distribution or density of [3H]L-NNA binding in the rat spleen obtained after lipopolysaccharide treatment despite induction of NOS type II catalytic activity. Our data suggest that an ischemic/excitotoxic insult up-regulates type I NOS gene expression and [3H]L-NNA binding and that this up-regulation may play a pivotal role in the pathogenesis of ischemic/excitotoxic diseases.

Topics: Animals; Autoradiography; Enzyme Inhibitors; Excitatory Amino Acid Agonists; Female; Ischemic Attack, Transient; Male; Mice; Mice, Mutant Strains; N-Methylaspartate; Nitric Oxide Synthase; Nitroarginine; Radioligand Assay; Rats; Tissue Distribution; Tritium

We hypothesize that the interaction between protein kinase C (PKC) and nitric oxide (NO) plays a role in the modulation of cerebral vascular tone, and the disturbance of this interaction following subarachnoid hemorrhage (SAH) results in vasospasm. To prove this hypothesis with direct evidence, PKC activities of smooth muscle cells of canine basilar arteries in the control and in the SAH groups were measured by an enzyme immunoassay method. N omega-nitro-L arginine (L-NA), an inhibitor of NO production, enhanced PKC activity. This enhancement was inhibited neither by 8-bromo-guanosine 3',5'-cyclic monophosphate (8-bromo-cGMP) nor SIN-1, a NO releasing agent. PKC activity in the SAH was significantly higher than in the control; however, no further enhancement was produced with L-NA. In the SAH, PKC activity was not inhibited either by 8-bromo-cGMP or SIN-1. We conclude that NO maintains an appropriate vascular tone through inactivation of PKC, and that this effect is disturbed following SAH, resulting in PKC-dependent vascular contraction, such as vasospasm. On the other hand, once PKC has been activated, NO precursors do not inhibit PKC. These facts indicate NO inactivates PKC through the inhibition of phosphatidylinositol breakdown.

Topics: Animals; Basilar Artery; Cyclic GMP; Dogs; Enzyme Activation; Enzyme Inhibitors; Female; Immunoenzyme Techniques; Ischemic Attack, Transient; Male; Molsidomine; Muscle, Smooth, Vascular; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Protein Kinase C; Reference Values; Subarachnoid Hemorrhage

Transient cerebral ischemia in fetal sheep is followed by a period of delayed cerebral injury associated with cerebral vasodilation. As nitric oxide (NO) can mediate both vasodilation and neuronal death, this study investigated whether inhibition of NO synthesis would attenuate the vasodilation and decrease cerebral injury. Eleven late gestation (range 122-133 d) fetal sheep were subjected to 30 min of transient cerebral ischemia in utero. Two hours later, treatment group (n = 5) received a continuous infusion of NG-nitro-L-arginine (L-NNA) at a dose of 50 mg.h-1 for 4 h followed by 20 mg.h-1 for the subsequent study period, a competitive inhibitor of NO synthase (NOS), whereas a control group (n = 6) received PBS. Inhibition of NOS activity was confirmed in the treatment group by 1) suppression of the fall in mean arterial blood pressure (MAP) associated with acetylcholine (p < 0.01), and 2) persistent increase in MAP after commencement of L-NNA (p < 0.05). Changes in cerebral blood volume (CBV) were observed for 3 d by measuring changes in concentration of total cerebral Hb ([tHb]) using near infrared spectroscopy. The delayed increase in CBV commenced at 13.1 +/- 1.0 h postischemia in the control and 12.7 +/- 2.3 h in the treatment group. Maximum increase at 30-36 h was 0.5 +/- 0.1 mL.100 g-1 in the treatment group and 1.2 +/- 0.2 mL.100 g-1 in the control (p < 0.05). Final CBV was depressed below preischemic baseline in the treatment (-0.7 +/- 0.2 mL.100 g-1) but not the control group (-0.1 +/- 0.3 mL.100 g-1) (p < 0.05). Neuronal loss, quantified histologically 3 d postischemia, indicated that cerebral injury was increased in the treatment group (p < 0.05). The results indicate that after transient cerebral ischemia in fetal sheep, NOS inhibition attenuates the delayed rise in CBV but does not decrease the extent of cerebral injury.

Topics: Animals; Cerebrovascular Circulation; Electroencephalography; Embryonic and Fetal Development; Enzyme Inhibitors; Gestational Age; Ischemic Attack, Transient; Nitric Oxide Synthase; Nitroarginine; Random Allocation; Reaction Time; Sheep; Vasodilation

Effect of ETA-receptor antagonist, BQ123, on postischemic hypoperfusion in the presence or absence of nitric oxide synthetase inhibitor, N omega-nitro-L-arginine (NLA), was investigated in Mongolian gerbils. BQ123 given prior to ischemia reversed the early incomplete recovery of cerebral blood flow observed with NLA without affecting the late postischemic hypoperfusion. Additional postischemic administration of BQ123 also reversed (P < 0.01) the late postischemic hypoperfusion seen in NLA-, N omega-nitro-D-arginine methyl ester- or Ringer's-treated animals.

Topics: Animals; Blood Pressure; Cerebrovascular Circulation; Endothelin Receptor Antagonists; Enzyme Inhibitors; Female; Gerbillinae; Ischemic Attack, Transient; Nitric Oxide Synthase; Nitroarginine; Peptides, Cyclic; Receptor, Endothelin A; Receptors, Endothelin; Temperature

The purpose of the present study was to clarify the effect of topical administration of a nitric oxide synthase inhibitor on extracellular glutamate concentration in transient forebrain ischemia. Two microdialysis probes were inserted into the bilateral striata of Wistar rats. NG-Nitro-L-arginine (L-NNA) with or without L-arginine was topically administered into the unilateral striatum through one of the microdialysis probes, while Ringer's solution was perfused into the contralateral striatum as the control, and 14 minutes of forebrain ischemia was applied. The extracellular glutamate concentration during ischemia and subsequent reperfusion was statistically significantly higher on the 100 microM L-NNA-perfused side than on the control side, but 1 mM L-NNA was ineffective. When 100 microM L-NNA was perfused together with 500 microM L-arginine, the glutamate concentration did not differ from that on the control side. Moreover, administration of 500 microM L-arginine significantly suppressed the glutamate elevation after reperfusion. The fact that the lower dose of L-NNA increased the accumulation of glutamate during ischemia and reperfusion without altering blood flow may indicate that nitric oxide affords protection against ischemia neuronal damage. However, since the higher dose of L-NNA did not affect the glutamate concentration, it appears that the effect of nitric oxide on extracellular glutamate concentration in forebrain ischemia differs, depending on the degree of the inhibition of NOS activity.

Topics: Animals; Cerebrovascular Circulation; Corpus Striatum; Drug Evaluation, Preclinical; Enzyme Inhibitors; Glutamic Acid; Ischemic Attack, Transient; Male; Microdialysis; Neurons; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Prosencephalon; Rats; Rats, Wistar

We planned a study to determine whether or not the mechanism of nitric oxide (NO) neurotoxicity involves the elevation of extracellular glutamate or changes of brain temperature in the pathogenesis of delayed neuronal death of gerbil hippocampal CA1 neurons following 5-min transient forebrain ischemia. Intraventricular injection of 5 microliters of 5.0 mg/ml N omega-nitro-L-arginine (LNNA) significantly preserved neuronal density in the central part of the CA1 region examined 7 days after 5-min ischemia [188.5 +/- 8.5/mm: 90.0% of the 209.5 +/- 11.1/mm density in the sham-operated controls vs. 16.7 +/- 6.4/mm in those injected with artificial cerebrospinal fluid (CSF) only]. There was no difference between these two groups in hippocampal temperature before, during or after 5-min ischemia. The glutamate concentration ([Glu]) during 5-min ischemia measured by a microdialysis technique was similar in the two groups (peak [Glu.] = 2.76 +/- 0.62 pmol/microliters dialysate in the artificial CSF group and = 2.93 +/- 0.64 pmol/microliters dialysate in the LNNA group). It was found that the neuronal toxicity of NO does not involve hyperthermia or the increase of extracellular glutamate concentration in the hippocampal CA1 region during 5-min ischemia.

Topics: Analysis of Variance; Animals; Body Temperature Regulation; Brain; Cell Death; Enzyme Inhibitors; Gerbillinae; Glutamic Acid; Hippocampus; Ischemic Attack, Transient; Male; Neurons; Neuroprotective Agents; Nitric Oxide Synthase; Nitroarginine

We investigated the putative role of nitric oxide in the expression of neuronal injury following both transient severe forebrain ischemia (CA1 neuronal injury) and transient or permanent middle cerebral artery occlusion (neocortical pannecrosis). Using the four-vessel occlusion model and increasing doses of N-omega-nitro-L-arginine, 2-40 mg/kg, we were unable to demonstrate any reduction in the percentage of CA1 cells injured following 10 min of transient severe forebrain ischemia followed by seven days of reperfusion. Higher doses proved toxic insofar as they increased the mortality following the ischemic insult. Saline-treated animals (n = 8) had 77 +/- 10% CA1 injury while those treated with 2 mg/kg of nitro-arginine i.v. had 80 +/- 7% (n = 7), and those with 10 mg/kg i.v. had 78 +/- 11% (n = 8). Two of five rats given 20 mg/kg i.v., three of eight given 40 mg/kg i.v., and two of six given 10 mg/kg i.v. followed by 3 x 10 mg/kg i.p., died. Of those treated with high-dose nitro-arginine and which survived ischemia and seven days' reperfusion, no significant reduction in CA1 injury was detected. Wistar rats and spontaneously hypertensive rats treated with either saline or nitro-arginine i.v. were exposed to 2 h of transient middle cerebral artery occlusion followed by 22 h of reperfusion. There were seven animals in each group. Wistars treated with saline had 198 +/- 67 mm3 (mean +/- S.D.) of neocortical infarction, and those treated with 10 m/kg of nitro-arginine i.v. had 199 +/- 93 mm3. Spontaneously hypertensive rats, transiently ischemic, treated with saline had 164 +/- 25 mm3 of infarct volume, while those treated with 2 mg/kg i.v. had 151 +/- 53 mm3, and those treated with 10 mg/kg i.v. had 145 +/- 29 mm3. Animals treated with 40 mg/kg i.v. had a nonsignificantly larger mean infarct volume (191 +/- 81 mm3). High dose nitro-arginine caused an increase in hypertension in the spontaneously hypertensive rats and increased the severity of focal ischemia as measured by intra-ischemic regional cerebral blood flows. A final group of seven spontaneously hypertensive rats underwent permanent middle cerebral artery occlusion and repeated dosing with N-omega-nitro-L-arginine i.p. In these animals an infarct volume of 234 +/- 60 mm3 was observed, which was again not statistically different from saline-treated controls (208 +/- 43 mm3, n = 7).(ABSTRACT TRUNCATED AT 400 WORDS)

Topics: Amino Acid Oxidoreductases; Animals; Arginine; Blood Gas Analysis; Blood Pressure; Cell Death; Cerebral Arteries; Cerebral Infarction; Ischemic Attack, Transient; Male; Necrosis; Neurons; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Inbred SHR; Rats, Wistar

The extensive research concerning the interaction between nitric oxide (NO) and ischemic brain tissue has yielded contradictory results. The present study was designed to explore the effect of gradual inhibition of NO production on brain ischemia. Gerbils were administered (i.p.) either saline (control-ischemia), or 5, 10, 25 or 50 mg/kg of NG-nitro-L-arginine (NARG), a specific inhibitor of NO synthase (NOS), and 4 h later were subjected to 5 min of forebrain ischemia. A group receiving 50 mg/kg NARG with sham operation served as a second control (control-NARG) group. Body weights and spontaneous activity were monitored daily until day 6, when the gerbils were sacrificed and their brains processed for histologic-morphometric evaluation. All ischemia groups displayed significant decreases in body weights starting on day 1, as compared to control-NARG (non-ischemic) gerbils. At 24 h post-ischemia spontaneous activity was increased in all ischemia groups in a dose-dependent manner, reaching a peak at 25 mg/kg. Typical ischemia-induced neuronal cell degeneration was observed at the hippocampal CA1 layer in control-ischemia and in each of the dose-groups of 10 mg/kg NARG and above. The 5 mg/kg group displayed damage which was not different from control-NARG, and was milder (P < 0.01) than control-ischemia gerbils and each of the other dose-groups. It is suggested that during ischemia, NO activates a series of processes which are beneficial to brain tissue, whereas an excess amount of NO causes neurotoxic effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Amino Acid Oxidoreductases; Animals; Arginine; Dose-Response Relationship, Drug; Gerbillinae; Hippocampus; Hyperkinesis; Ischemic Attack, Transient; Male; Nitric Oxide Synthase; Nitroarginine

N omega-nitro-L-arginine (0.3-10 mg/kg), a nitric oxide (NO) synthase inhibitor, was administered i.p. to gerbils subjected to 10 min of carotid artery occlusion seven times at 5 min, 3, 6, 24, 48, 72 and 96 h after recirculation. Histopathological examination of the brains obtained 6 days after reflow disclosed that N omega-nitro-L-arginine possesses an ability to mitigate neuronal necrosis in the CA1 subfield of the hippocampus with an optimal dosage of 3 mg/kg. These results strongly suggest that NO synthase activation is at least partly involved in the pathogenetic cellular mechanisms underlying selective neuronal necrosis following cerebral ischemia.

Topics: Amino Acid Oxidoreductases; Animals; Arginine; Dose-Response Relationship, Drug; Gerbillinae; Hippocampus; Image Processing, Computer-Assisted; Injections, Intraperitoneal; Ischemic Attack, Transient; Male; Necrosis; Neurons; Nitric Oxide Synthase; Nitroarginine

Nitric oxide has been implicated as a mediator of glutamate excitotoxicity in primary neuronal cultures.. A number of indicators of brain nitric oxide production (nitric and cyclic guanosine monophosphate [cGMP] concentrations and nitric oxide synthase activity) were examined after bilateral carotid ligation and right middle cerebral artery occlusion in adult rats.. Brain nitrite was significantly increased in the right versus left cortex 5, 10, and 20 minutes after middle cerebral artery occlusion (P < .05), with a return to baseline at 60 minutes. There were no significant changes in cerebellar concentrations. Cortical levels of cGMP were increased at 10, 20, and 60 minutes after occlusion, with significant right-to-left differences (P < .05). Cerebellar concentrations of cGMP were also increased but without significant side-to-side differences. Nitric oxide synthase activity increased approximately 10-fold from baseline 10 minutes after occlusion in the right cortex but decreased markedly by 60 minutes from its peak at 10 minutes. The right-to-left difference in nitric oxide synthase activity was significant at 20 minutes (P < .05). Pretreatment of rats with NG-nitro-L-arginine, a nitric oxide synthase inhibitor, abolished the rise in nitrite and cGMP.. These results suggest that a sharp transient increase in the activity of nitric oxide synthase occurs during the first hour of cerebral ischemia, which leads to a burst in nitric oxide production and activation of guanylate cyclase.

Topics: Amino Acid Oxidoreductases; Analysis of Variance; Animals; Arginine; Arterial Occlusive Diseases; Brain; Cerebellum; Cerebral Arterial Diseases; Cerebral Cortex; Cyclic GMP; Functional Laterality; Ischemic Attack, Transient; Male; Nitric Oxide; Nitric Oxide Synthase; Nitrites; Nitroarginine; Rats; Rats, Wistar

We investigated whether inhibition of nitric oxide (NO) biosynthesis with N-omega-nitro-L-arginine (NNA), a competitive inhibitor of NO synthase (NOS), would modify the volume of the focal ischemic infarction produced by occlusion of the middle cerebral artery (MCA) in spontaneously hypertensive rats. NNA was infused for 1 h (2.4 mg/kg/h) immediately following occlusion of the MCA. NNA increased lesion volume 24 h later by 32% over controls (150.8 +/- 16.6 to 199.2 +/- 17.4 mm3; p less than 0.001, n = 6). This effect was antagonized by co-infusion of L- but not D-arginine. The antihypertensive rilmenidine (0.75 mg/kg) reduced the lesion by 27% (p less than 0.05, n = 4). Changes in lesion size were confined to the penumbra. NNA increased arterial pressure (AP) (118 +/- 8.9 to 149 +/- 16.0 mm Hg; p less than 0.01, n = 3) but did not change regional CBF. However, elevation of AP did not change the lesion volume or distribution. We conclude that inhibition of the constitutive form of NOS in vivo increases the volume of focal ischemic infarction as a consequence of reduced NO biosynthesis. The absence of NO availability may extend lesion formation by inhibition of reactive hyperemia, platelet disaggregation, and/or release of neuroprotective neuromodulators in the penumbra, which may counteract and override any of its neurotoxic actions.

Topics: Amino Acid Oxidoreductases; Analysis of Variance; Animals; Antihypertensive Agents; Arginine; Cerebral Infarction; Ischemic Attack, Transient; Male; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Oxazoles; Phenylephrine; Rats; Rats, Inbred WKY; Rilmenidine

Experiments were performed with Mongolian gerbils to study the effect of the specific nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine (L-NNA) on ischemic brain damage induced by 5 min bilateral carotid occlusion. A single i.p. injection of L-NNA did not result in any neuronal loss in the central nervous system. In animals undergoing ischemia, a selective destruction of hippocampal CA1 cells was observed whereas pretreatment with 50 mg/kg L-NNA 4 h before administration of ischemia produced significantly more extensive cell damage in the hippocampus and other brain regions. These findings demonstrate that in this model inhibition of nitric oxide generation augments ischemia-induced neuronal cell injury in the brain.

Topics: Animals; Arginine; Cell Death; Gerbillinae; Hippocampus; Ischemic Attack, Transient; Male; Motor Activity; Neurons; Nitroarginine

Topics: Animals; Arginine; Cell Death; Cerebral Infarction; Dizocilpine Maleate; Ischemic Attack, Transient; Mice; Neurons; Nitric Oxide; Nitroarginine; Signal Transduction