[Effect of adaptation to hypoxia on expression of NO synthase isoforms in rat myocardium].

Previously we have shown that adaptation to hypoxia (AH) is cardio- and vasoprotective in myocardial ischemic and reperfusion injury and this protection is associated with restriction of nitrosative stress. The present study was focused on further elucidation of NO-dependent mechanisms of AH by identifying specific NO synthases (NOS) that could play the major role in AH protection. AH was performed in a normobaric hypoxic chamber by breathing hypoxic gas mixture (9.5-10% O2) for 5-10 min with intervening 4 min normoxia (5-8 cycles daily for 21 days). Expression of neuronal (nNOS), inducible (iNOS), and endothelial (eNOS) protein was measured in the left ventricular myocardium using Western blot analysis with respective antibodies. AH educed iNOS protein expression by 71% (p < 0.05) whereas eNOS protein expression tended to be reduced by 41% compared to control (p < 0.05). nNOS protein expression remained unchanged after AH. Selective iNOS inhibition can mimic the AH-induced protection. Therefore protective effects of AH could be at least partially due to restriction of iNOS and, probably, eNOS expression.

[Vasoprotective effect of adaptation to hypoxia in myocardial ischemia and reperfusion injury].

Adaptation to hypoxia is known to be cardioprotective in ischemic and reperfusion (IR) injury of the myocardium. This study was focused on investigating a possibility for prevention of endothelial dysfunction in IR injury of the rat heart using adaptation to intermittent hypoxia, which was performed in a cyclic mode (5-10 min of hypoxia interspersed with 4 min of normoxia, 5-8 cycles daily) for 21 days. Endothelial function of coronary blood vessels was evaluated after the in vitro IR of isolated heart (15 min of ischemia and 10 min of reperfusion) by the increment of coronary flow rate in response to acetylcholine. Endothelium-dependent relaxation of isolated rat aorta was evaluated after the IR myocardial injury in situ (30 min of ischemia and 60 min of reperfusion) by a relaxation response of noradrenaline-precontracted vessel rings to acetylcholine. The following major results were obtained in this study: 1) IR myocardial injury induced endothelial dysfunction of coronary blood vessels and the aorta, a non-coronary blood vessel, remote from the IR injury area; and 2) adaptation to hypoxia prevented the endothelial dysfunction of both coronary and non-coronary blood vessels associated with the IR injury. Therefore, adaptation to hypoxia is not only cardioprotective but also vasoprotective in myocardial IR injury.

[Role of restricted nitric oxide overproduction in the cardioprotective effect of adaptation to intermittent hypoxia].

Adaptation to intermittent normobaric hypoxia is cardioprotective and can stimulate nitric oxide (NO) synthesis. However the role of nitric oxide (NO) in prevention of ischemia-reperfusion (IR) injury of myocardium is controversial. This study was focused on evaluating the effect of adaptation to hypoxia and IR on NO production and development of nitrative stress in the myocardium. Adaptation to hypoxia tended to increase NO production, which was determined by the total level of plasma nitrite and nitrate, and prevented IR-induced NO overproduction. The IR-induced NO overproduction was associated with significant 3-nitrotyrosine (3-NT) accumulation in the left ventricle but not in septum or aorta. In hypoxia-adapted rats, 3-NT after IR was similar to that of control rats without IR. IHC induced marked accumulation of HIF-1alpha in the left ventricle. We suggest that HIF-1alpha contributes to NO-synthase expression during adaptation to hypoxia and thereby facilitates the increase in NO production. NO, in turn, may subsequently prevent NO overproduction during IR by a negative feedback mechanism.

Mechanism of adaptation of the vascular system to chronic changes in nitric oxide level in the organism.

We studied the possibility of directed modulation of the efficiency of NO storage in rats due to adaptation to the chronic changes in plasma NO level. The efficiency of NO storage increased during long-term maintenance of high plasma level of NO and decreased in NO-deficient states. The compensatory changes in NO storage capacity of vessels depending on its organism content represent a new mechanism of adaptation of the cardiovascular system to chronic excess or deficit of NO, while directed modulation of this process can be important for the protection of the organism against both surplus or shortage of NO.

Detection and description of various stores of nitric oxide store in vascular wall.

We analyzed the possibility of the existence of various NO pools in the vascular wall. Incubation of isolated rat aorta with dinitrosyl iron complex (NO donor) led to the formation of NO stores in the vascular wall detected by vascular relaxation response induced by diethyldithiocarbamate and N-acetylcysteine. Comparison of the effects of successive application of diethyldithiocarbamate and N-acetylcysteine revealed two NO pools (one pool responded to both agents, while other responded only to N-acetylcysteine). Inhibition of guanylate cyclase with methylene blue abolished the response to diethyldithiocarbamate, while the reaction to N-acetylcysteine decreased by the value, corresponding to diethyldithiocarbamate-dependent relaxation. It is hypothesized that in the vascular wall NO is stored in the form protein-bound dinitrosyl iron complexes and S-nitrosothiols in hydrophilic and hydrophobic cell compartments.

[Nitric oxide storage in the cardiovascular system]. / Deponirovanie oksida azota v serdechno-sosudistoi sisteme.

Nitric oxide (NO) is a highly reactive substance with short lifetime. In conditions of a living organism NO can be bound by the complexes used for transport and intracellular storage of NO. The main biological forms of NO store include S-nitrosothiols and dinitrosyl iron complexes capable of interconversion. The NO store formed by these complexes in the vascular wall, on the one hand, provides for protection from excessive free NO after its overproduction and, on the other hand, can be an additional NO source when it is deficient. Apparently, the efficiency of NO storage is genetically determined and corresponds to the inherited level of NO production in the organism. Controlled modulation of formation and dissociation of the NO store is a promising trend for further investigation.

[Catecholamines, nitrogen oxide, and resistivity to stressor lesions: effect of adaptation to hypoxia]. / Katekholaminy, oksid azota i ustoichivost' k stressornym povrezhdeniiam: vliianie adaptatsii k gipoksii.

Pronouncement of stress-induced disturbance of searching behaviour (using "open field" test) and stomach ulceration were compared for the first time with activity of the catecholamine system in hypothalamus and striatum and also with activity of the stress-limiting system of nitric oxide (NO) in the rats of two strains August and Wistar, which differ in their resistance against stress-induced cardiovascular disorders. The effect of prior adaptation to hypobaric hypoxia on these disorders was also studied. August rats appeared to be more resistant than Wistar rats against stress-induced disturbance of the searching behaviour and stomach ulceration. Results of measuring the content of catecholamines in brain structures and the content of NO stable metabolites nitrate/nitrite in plasma suggested that these differences could be due to the stress activation of the nigro-striatal dopaminergic system in August rats, which was not observed in Wistar rats, and also to the higher production of NO in August than in Wistar rats. Adaptation to hypoxia considerably restricted these stress disorders in rats of both strains. Importantly, the protective effects were associated with activation of the nigro-striatal dopaminergic system in all the animals. In the result, adapted Wistar rats, as distinct from non-adapted Wistar rats, displayed a stress activation of this system. The protective effects of adaptation were also accompanied by an increased NO synthesis. Taken together, the data suggest an important role of the responsiveness of the brain dopaminergic system and NO system in the mechanism of resistance against stress-induced disturbances.

HSP70 stress proteins, nitric oxide, and resistance of August and Wistar rats to myocardial infarction.

Accumulation of HSP70 stress proteins in the myocardium and blood content of nitrite/nitrate in August rats with modeled myocardial infarction surpassed these parameters in Wistar rats less resistant to cardiovascular disorders by 2-2.5 and 1.8 times, respectively. Our results suggest that various resistance of August and Wistar rats to myocardial infarction is related to genetically determined differences in the activity of HSP70 and nitric oxide systems.

[Correction of NO-dependent cardiovascular disorders by adaptation to hypoxia]. / Korrektsiia NO-zavisimykh serdechno-sosudistykh narushenii s pomoshch'iu adaptatsii k gipoksii.

Spontaneously hypertensive rats (SHR-SP) were adapted to intermittent hypobaric hypoxia in an altitude chamber for 40 days. The adaptation to hypoxia prevented an excessive endothelium-dependent relaxation and hypotension characteristic of myocardial infarction. The adaptation also attenuated the increase in blood pressure and prevented impairment of the endothelium-dependent relaxation in SHR-SP. The universal nature of the adaptation allows to use it for correcting many cardiovascular disorders related to diverse alterations of NO metabolism.

[The role of preventing nitric oxide deficiency in the antihypertensive effect of adaptation to hypoxia]. / Rol' preduprezhdeniia defitsita oksida azota v antigipertenzivnom éffekte adaptatsii k gipoksii.

Shortage of endothelial nitric oxide (NO) manifested as decreased daily urinary excretion of nitrate and nitrite as well as attenuated endothelium-dependent relaxation of conduit and resistance vessels progresses with age-related increase of blood pressure (BP) in stroke-prone spontaneously hypertensive rats (SHRSP). Simultaneous NO-dependent suppression of vascular contractions is, apparently, due to the inducible NO synthase activity in vascular smooth muscle specific for spontaneously hypertensive rat. Adaptation of rats to hypobaric hypoxia initiated at early hypertensive stage (at the age of 5-6 weeks) decelerates hypertension progress. The antihypertensive effect of the adaptation was accompanied by stimulation of endothelial NO synthesis and prevention of impaired NO-dependent response in isolated blood vessels. Nitric oxide stores were formed in the vascular wall of SHRSP and WKY rats at the same time. The obtained data indicate a significant role of correction of endothelial NO deficiency in the antihypertensive effect of adaptation to hypoxia.

[Hypoxia and nitric oxide]. / Gipoksiia i oksid azota.

Cell death or survival under hypoxia is determined to a greater extent by the nature of changes in nitric oxide (NO) metabolism. Severe hypoxia causes NO overproduction that is an important factor that induces apoptotic cell death. In contrast, a cell response to moderate hypoxia enhances hypoxic resistance and restricts the mechanisms of activated apoptosis. A moderate increase in NO synthesis and storage that are characteristic of hypoxic adaptation may limit NO overproduction induced by acute hypoxia. In addition, NO-dependent mechanisms of adaptation are apparently involved in the restriction of apoptosis-specific signaling pathways. Therefore, during hypoxic adaptation, NO acts as an endogenous protective agent involved in the limitation of severe hypoxia-induced cell damages.

[Nitrogen oxide storage as a factor of adaptive defence]. / Deponirovanie oksida azota kak faktor adaptivnoi zashchity]

Adaptation to environmental factors possesses multiple NO-dependent protective effects and stimulates the NO storage. An adaptation to a mild stress was shown to reduce the death rate in rats from 57% to 8% and to prevent a heat shock-induced hypotension and endothelial overactivation. Treatment of the rats with the NO-synthase inhibitor L-NNA interfered with the NO storage and formation of protective effects, while the NO donor dinitrosyl iron complex facilitated the NO storage and simulated the adaptive defence. The data obtained suggest an important role of the NO storage in adaptive defence of the organism.

Role of nitric oxide in adaptation to hypoxia and adaptive defense.

Adaptation to hypoxia is beneficial in cardiovascular pathology related to NO shortage or overproduction. However, the question about the influence of adaptation to hypoxia on NO metabolism has remained open. The present work was aimed at the relationship between processes of NO production and storage during adaptation to hypoxia and the possible protective significance of these processes. Rats were adapted to intermittent hypobaric hypoxia in an altitude chamber. NO production was determined by plasma nitrite/nitrate level. Vascular NO stores were evaluated by relaxation of the isolated aorta to diethyldithiocarbamate. Experimental myocardial infarction was used as a model of NO overproduction; stroke-prone spontaneously hypertensive rats (SHR-SP) were used as a model of NO shortage. During adaptation to hypoxia, the plasma nitrite/nitrate level progressively increased and was correlated with the increase in NO stores. Adaptation to hypoxia prevented the excessive endothelium-dependent relaxation and hypotension characteristic for myocardial infarction. At the same time, the adaptation attenuated the increase in blood pressure and prevented the impairment of endothelium-dependent relaxation in SHR-SP. The data suggest that NO stores induced by adaptation to hypoxia can either bind excessive NO to protect the organism against NO overproduction or provide a NO reserve to be used in NO deficiency.

[Nitric oxide storage in rats of various genetic strains and its role in the antistressor effect of adaptation to hypoxia]. / Deponirovanie oksida azota u krys raznykh geneticheskikh linii i ego rol' v antistressornom éffekte adaptatsii k gipoksii.

Adaptation to hypobaric hypoxia induced a gradual increase in the NO production along with a progressive NO storage in vascular wall. Unadapted August rats were more resistant against stress-induced stomach ulceration than the Wistar rats. Following a 6-day adaptation rats of both strains revealed a protective antiulcerogenic effect. A long-term adaptation potentiated the stress damage of the stomach rather than protected against it. A higher basal NO production seems to provide a more efficient antistress defence in the August rats. An intense NO storage may create a relative NO shortage and thus predispose to stress-induced vasoconstriction and ulceration.

Production and storage of nitric oxide in adaptation to hypoxia.

Adaptation to hypobaric hypoxia is known to exert multiple protective effects related with nitric oxide (NO). However the effect of adaptation to hypoxia on NO metabolism has remained unclear in many respects. In the present work we studied the interrelation between NO production and storage in the process of adaptation to hypoxia. The NO production was determined by the total nitrite/nitrate concentration in rats plasma. The volume of NO store was evaluated in vitro by the magnitude of isolated aorta relaxation to diethyldithiocarbamate. It was shown that both the nitrite/nitrate level and the NO store increased as adaptation to hypoxia developed. Furthermore, the NO store volume significantly correlated with plasma nitrite/nitrate. Therefore, adaptation to hypoxia stimulates NO production and storage and these effects can potentially underlie NO-dependent beneficial effects of adaptation.

[The production and deposition of nitric oxide during adaptation to hypoxia]. / Produktsiia i deponirovanie oksida azota pri adaptatsii k gipoksii.

It is common knowledge that adaptation to hypobaric hypoxia provides for a number of protective NO-dependent effects in the organism. However, many aspects of its influence on NO metabolism remain unclear. In this work we studied the relationship between NO production and deposition in the course of adaptation to hypoxia. No production was assayed by the total concentration of nitrates and nitrites in rat serum, while the volume of NO depot was determined from the level of isolated aorta relaxation in response to diethyldithiocarbamate in vitro. In the course of adaptation to hypoxia, nitrate and nitrite concentration increases as well as NO deposition in the vascular wall. The volume of NO depot correlated reliably with the serum concentration of nitrates and nitrites. Hence, adaptation to hypoxia increases NO production and deposition, which can underlie its NO-dependent protective effects.