Protective Role of Nitrate/Nitrite Reductase System during Transient Global Cerebral Ischemia.

The effects of a non-selective blocker of NO synthases LNNA in a dose of 25 mg/kg and nitrates KNO3, NaNO3, Mg(NO3)2, and Ca(NO3)2 in doses of 5 and 50 mg/kg were studied on the model of experimental ischemic stroke induced by bilateral occlusion of the common carotid arteries. Wistar rats were randomized into 40 treatment (n=960) and 8 control (n=192) groups. Treatment group rats received injection of either nitrate, or LNNA, or a combination LNNA+nitrate. All substances were administered intraperitoneally 1 h prior to brain ischemia or 5 sec after occlusion of the common carotid arteries. Control rats received the same volume of 0.9% NaCl at the same terms. The non-selective inhibitor of NO synthases LNNA administered against the background of brain ischemia increased neurological deficit and animal mortality. Nitrate/nitrite reductase system had protective properties depending on the cation of nitrate and concentration of a nitrate during inhibition of NO synthase system under conditions of brain ischemia and hypoxia.

Effect of Sodium Nitrite and L-NNA on the Outcome of Experimental Ischemic Stroke.

We studied the effect of sodium nitrite in doses of 5 and 50 mg/kg and NO synthase inhibitor L-NNA in a dose of 20 mg/kg on the course of experimental ischemic stroke caused by occlusion of both carotid arteries. Sodium nitrite and NO synthase inhibitor were administered 1 h prior to occlusion of еру carotid arteries and 5 sec after brain ischemia. Sodium nitrite in a dose of 5 mg/kg had a protective effect on the time course of neurological disorders and reduced animal mortality. NO synthase inhibitor L-NNA aggravated the neurological symptoms.

[Inhibitors of neuronal and inducible NO-syntases enhance the effect of short-term adaptation to hypoxia in rats of Krushinsky-Molodkina strain].

We found that selective inhibitors of neuronal and inducible NOS (7-nitroindazole and aminoguanidine) significantly enhance the protective effect of short-term adaptation to hypoxia on the development of stress lesions in rats Krushinsky-Molodkina.

[A protective role of the nitrite/nitrate reductase system in ischemic stroke]. / Protektivnaya rol' nitrit/nitrat-reduktaznoi sistemy pri ishemicheskom insul'te.

OBJECTIVE: To reveal a protective role of the nitrite/nitrate reductase system in NO- synthase (NOS) inhibition in ischemic stroke. MATERIAL AND METHODS: An effect of the non-selective NOS inhibitor Nω-nitro-L-arginine (L-NNA) introduced in dose of 25 mg/kg and nitrates (КNO3, NaNO3, Mg(NO3)2, Ca(NO3) in doses of 5 mg/kg) on ischemic stroke induced by the occlusion of carotid arteries in an experimental model was studied. The animals (Wistar rats) were stratified into 20 experimental groups (n=480) and 4 control groups (n=96). One of nitrates or L-NNA along with one of nitrates or L-NNA alone were administered to experimental groups 1h before brain ischemia or 5s after carotid artery occlusion. 0.9% NaCl was used in the control rats. RESULTS: L-NNA increases neurological deficit and lethality in brain ischemia. Depending on a cation, the nitrite/nitrate reductase system may play a protective role in the inhibition of NOS-system in brain ischemia. CONCLUSION: In brain ischemia and NOS inhibition, Mg(NO3)2 has the greatest protective effect.

Protective effect of magnesium nitrate against neurological disorders provoked by cerebral ischemia in rats.

The study examined effects of inorganic magnesium agents: magnesium nitrate Mg(NO3)2, magnesium sulfate MgSO4, and magnesium chloride MgCl2 on the development of neurological disorders and mortality in rats resulting from cerebral ischemia provoked by a single-stage bilateral occlusion of the common carotid arteries. The rats were injected with one of examined magnesium preparations (5 mg/1 kg body weight) 1 h prior to or 1-2 sec after occlusion. The control group rats were treated with physiological saline at the same terms. Irrespective of the moment of injection, magnesium nitrate demonstrated significant protective effect on dynamics of neurological disorders and mortality, while similar effects of magnesium sulfate and magnesium chloride were insignificant.

[The influence of inhibitors of neuronal and inducible NO-synthases on experimental hemorrhagic stroke]. / Vliianie ingibitorov neironal'noi i indutsibel'noi NO-sintaz na razvitie gemorragicheskogo insul'ta v éksperimente.

Objectives. To study the effect of inhibitors of neuronal and inducible NO-synthase on the development of hemorrhagic stroke in rats Krushinsky-Molodkina (KM) without adaptation to hypoxia and with short-term adaptation to hypobaric hypoxia. Material and methods. Ninety rats were included in the study. Experiments with short-term adaptation to hypobaric hypoxia were performed on 48 rats. The inhibitor of inducible NO-synthase (aminoguanidine, "Sigma") or the inhibitor of neuronal NO-synthase (7-nitroindasol, "Sigma") were injected in dosage 2.5 mg/100g intraperitoneally. Results. Selective inhibitors of neuronal and inducible NO-synthase had a protective effect on stress injuries in KM rats. The inhibitor of neuronal NO-synthase was more effective than the inhibitor of inducible NO-synthase in the experiments without adaptation to hypoxia. Markedly greater protective effect was achieved by the simultaneous introduction of inhibitors of neuronal and inducible NO-synthase. The greatest protective effect in the development of stress damage in rats of KM was observed in short-term adaptation to hypobaric hypoxia with simultaneous introduction of both inhibitors. Conclusions. It can be assumed that an excessive amount of NO produced by neuronal and inducible NO-synthases during the acoustic exposure in KM rats leads to stress damage. Use of selective inhibitors reduce the excess NO synthesis and the development of audiogenic stress damage caused by hemorrhagic stroke.

[The effect of magnesium nitrate on the outcome of experimental acute ischemic stroke]. / Vliianie nitrata magniia na iskhod ostrogo éksperimental'nogo ishemicheskogo insul'ta.

Objectives. To explore the effect of inorganic forms of magnesium (magnesium nitrate, magnesium sulfate, magnesium chloride) on the course of experimental ischemic stroke (II). Material and methods. The experimental ischemic stroke caused by the occlusion of two carotid arteries in Wistar rats was studied. Animals were divided into 6 case (n=168) and 2 control groups (n=56). In case groups, magnesium was injected 1h before the occlusion of both carotid arteries and 1-2h after the brain ischemia. Control groups received physiological solution in the same periods. Results. Magnesium nitrate, regardless of the period of injection, had the significant positive effect on the dynamics of neurological lesions and mortality of animals. Conclusions. Magnesium nitrate meets the majority of criteria required for ideal pharmacological drugs: it is inexpensive, easy available, easy injectable and does not cause any serious adverse effects.

Effect of cation type and concentration of nitrates on neurological disorders during experimental cerebral ischemia.

Experiments were performed on the model of ischemic stroke due to bilateral occlusion of the carotid arteries. Nitrates had various effects on the dynamics of neurological disorders and mortality rate of Wistar rats, which depended on the cation type and concentration.

[The possible role of nitrogen dioxide produced in the field of bifurcation of vessels, in the processes of their damage in hemorrhagic strokes, and the formation of atherosclerotic plaques].

According to modern views the formation of atherosclerotic plaques is associated with accumulation of cholesterol in the vascular wall. This is due to an imbalance between the intake of cholesterol in the intima of vessels, together with the low-density lipoproteins (LDL) and its output with high-density lipoprotein (HDL). Change of LDL (glycosylation, lipid peroxidation, hydrolysis of phospholipids) and the effective release of cholesterol from the endothelium of the vascular wall are the factors that cause an imbalance in cholesterol metabolism. In this paper we propose a new concept of the mechanism of initial formation of atherosclerotic plaques, which can complement the existing concepts. According to this concept an important role in the early stages of atherosclerosis are highly reactive molecules of nitrogen dioxide (NO2), resulting from the violation of the cycles of nitric oxide and superoxide anion radical. Hypothesized that the mechanism of antiradical protection of cells and the organism as a whole, above all, laid out in most of the cyclic organization of metabolic processes that involve the formation of free radicals. Violation of this cyclic mechanism may be one of the causes of many diseases associated with hypoxia/ischemia and inflammation. The review considers the hypothesis of the possibility of participation of NO2 and OH-radicals formed in violation of the cycles of NO and superoxide, in the mechanisms of vascular damage with hemorrhagic stroke and in the formation of atherosclerotic plaques.

Effect of locomotor activity on ultrastructure of cerebellar neurons, neurological disturbances, and survival of Krushinsky-Molodkina rats with hemorrhagic stroke.

We studied the effect of locomotor activity on the ultrastructure of cerebellar neurons, neurological disturbances, and survival rate in Krushinsky-Molodkina rats during the development of hemorrhagic induced by acoustic stress. In animals with high spontaneous locomotor activity, severe edema of cerebellar neurons (resulting in the destruction of surrounding structures) and swelling of the synapses (terminals of mossy fibers on granule cell dendrites) were observed. By contrast, the areas of intracerebral, subdural, and subarachnoid hemorrhages were lower in rats under conditions of forced rest.

[The effect of nitrates on the outcome of acute experimental ischemic stroke].

Effects of nitrates NaNO(3), KNO(3), Mg(NO(3)) 2 on animals (Wistar rats) were studied on the basis of the experimental model of ischemic stroke induced by the occlusion of two carotid arteries. The animals were divided into two groups: the main group (n=60) and the control group (n=30). Three series of experiments were conducted. In each experiment, the rats of the main group were treated with one of nitrates and the control group was treated with physiological solution. It has been shown that nitrates exert either positive or negative effect depending on the cation type, nitrate concentration and the duration of their action on the dynamics of neurologic disturbances. Conditions of the development of neuroprotective effect of nitrates are discussed.

[Experimental hemorrhagic stroke: the effect of the peptide preparation cortexin in the formation of Hb-NO-complexes and other blood paramagnetic centers].

Using electronic paramagnetic resonance (EPR), we studied the effect of the peptide cortexin on the content of hemoglobin nitrozyl complexes (Hb-NO-complexes) and other paramagnetic centers (transferrin, methemoglobin) in the blood of rats of Krushynsky-Molodkina line in the experimental hemorrhagic stroke induced by acoustic stress. After the acoustic exposure, the level of Hb-NO-complexes have increased by more than 6 times. The intensity of the EPR signal of the plasma peptide transferrin increased by 1,5 times. The level of blood methemoglobin was also elevated, though not significantly, after the acoustic stress. Cortexin substantially reduces the formation of Hb-NO-complexes and, therefore, the level of nitride oxide while the contents of transferrin and methemoglobin remain intact.

Effect of inhibitors of inducible and neuronal NO synthases on the development of audiogenic stress-induced damage in Krushinskii-Molodkina rats.

Experiments on the models of epileptiform seizure and hemorrhagic stroke (Krushinskii-Molodkina rats) showed that selective inhibitors of inducible and neuronal NO synthases (aminoguanidine and 7-nitroindazole) significantly decrease the mortality rate, reduce the severity of motor disorders, and prevent the development of intracranial hemorrhages under conditions of audiogenic stress.

[EPR study of the influence of hypoxia on nitric oxide formation in the blood of Krushinskii-Molodkina rats].

The influence of hypoxia on nitric oxide formation in the blood of Krushinskii-Molodkina rats has been studied by electron paramagnetic resonance. It was found that nitric oxide synthesis in Krushinskii-Molodkina rats is increased compared with that in Wistar rats. A significant enhancement of the EPR signal of Hb-NO complexes in the animal blood was observed after hypoxia simulating the altitude of 5000 m above the sea level, in particular in the presence of sodium nitrite and the NO-synthase inhibitor L-nitroarginine. It was assumed that NO synthesis and nitro-/nitrite- reductase systems are activated under hypoxic conditions.

[Nitric oxide is involved in the protective effects of short-term adaptaion to hypoxia in the course of stress-induced disorders in Krushinsky-Molodkina rats].

A possible involvement of nitric oxide in the protective effect of short-term adaptation of Krushinsky-Molodkina rats to mild hypoxia simulating 5000 m above sea level was studied. Nitric oxide proved to have a considerable protective effect on stress-induced disorders in Krushinsky-Molodkina rats as demonstrated using NO-synthase inhibitors and NO monitoring by electron spin resonance under different experimental conditions.

[Antistress and angioprotective influence of nitric oxide in epilepsy-prone rats of Krushinskii-Molodkina strain].

In rats of Krushinsky-Molodkina strain (KMR), the audiogenic stress induced epileptiform seizure and development of acute disturbances of cerebral circulation of hemorrhagic nature. The inhibitor of NO-synthase (L-NNA) increased the severity of clinical symptoms, mortality, and the intensity of intracranial hemorrhages. In contrast, L-arginine elevated the resistance of KMRs to acoustic stress. The intensity of nitrergic innervation was analyzed in preparations of the middle cerebral artery with the use of histochemical NADPH-diaphorase staining. In preparations of control KMRs, a net of NADPH-positive perivascular nerve fibers was found, while in experimental KMRs, in an hour after sound stimulation, such fibers practically were not revealed. Preliminary exposure of KMRs in hypoxic conditions (1 hour in hypobaric chamber at simulated altitude of 5000 m above the sea level) decreased the development of stress lesions. The protective effect of hypoxic training disappeared after the administration of NO-synthase inhibitor (L-NNA). The study demonstrated participation of nitric oxide (NO) in adaptive reactions of cerebral hemodynamics linked with the significant increase of cerebral blood flow.

[Semax prevents elevation of nitric oxide generation caused by incomplete global ischemia in the rat brain]. / Semaks preduprezhdaet povyshenie generatsii oksida azota v mozge krys, obuslovlennoe nepolnoi global'noi ishemiei.

A twofold increase in the nitric oxide (NO) production and a moderate increase in the content of secondary products of lipid peroxidation was observed in Wistar rats with incomplete global ischemia model induced by the bilateral occlusion of common carotid arteries. A clear correlation was observed between the NO content in the rat brain and the level of neurological disturbance manifestations in the ischemized animals. The synthetic peptide semax (a fragment of ACTH4-7 Pro-Gly-Pro) in a dose of 0.3 mg/kg prevented from the development of both neurological disturbances and excess NO production in the rat brain cortex.