Brain blood flow modulates the neurotoxic action of hyperbaric oxygen via neuronal and endothelial nitric oxide.

Studies on conscious rats with inhibition of NO synthase were used to assess the dynamics of brain blood flow and EEG traces during hyperbaric oxygenation at 4 or 5 atm. Oxygen at a pressure of 4 atm induced cerebral vasoconstriction in intact animals and decreased blood flow by 11-18% (p < 0.05) during 60-min exposure to hyperbaric oxygenation. Paroxysmal EEG activity and oxygen convulsions did not occur in rats at 4 atm of O2. At 5 atm, convulsive activity appeared on the EEG at 41 +/- 1.9 min, and blood flow decreased significantly during the first 20 min; blood flow increased by 23 +/- 9%, as compared with controls, (p < 0.01) before the appearance of convulsions on the EEG. Prior inhibition of NO synthase I (NOS I) and NO synthase III (NOS III) with N(omega)-nitro-L-arginine methyl ester (L-NAME, 30 mg/kg) or inhibition only of NOS I with 7-nitroindazole (7-NI, 50 mg/kg) prevented the development of hyperoxic hyperemia and paroxysmal spikes on the EEG during hyperbaric oxygenation at 5 atm. These results show that hyperbaric oxygen induces changes in cerebral blood flow which modulate its neurotoxic action via nitric oxide synthesized both in neurons and in cerebral vessels.

[Cerebral blood flow modulates hyperbaric oxygen induced neurotoxicity by neuronal and endothelial nitric oxide]. / Mozgovoi krovotok moduliruet neirotoksicheskoe deistvie giperbaricheskogo kisloroda s pomoshch'iu neironal'nogo i endotelial'nogo oksida azota.

The goal of work was to reveal changes in microcirculation of the rat brain and the role of nitric oxide (NO) in development of seizures at hyperbaric oxygen exposure. The Wistar rats with implanted paired platinum electrodes in left and right striatum were used for experiments. The latency of seizures was defined by the EEG, the cerebral blood flow (CBF) was measured by hydrogen clearance. One group of animals was exposed to a 5-ata oxygen, while the others before oxygen treatment were injected with: Nw-nitro-L-arginine methyl ester (L-NAME), blockator of constitutive NO synthase; 7-nitroindozol (7NI), specific inhibitor of neural NO synthase. The latency of seizures was 41 +/- 1.9 min at 5 ata oxygen exposure. CBF was decreased to 10-14% but before seizures it increased to 23 +/- 9%. L-NAME and 7NI prevented development of hyperoxygen hyperemia and onset of seizures. The results indicate occurrence of hyperbaric oxygen changes of the CBF that modulate neurotoxic effects of NO in neurons as well as in cerebral vessels.

[Effect of hyperbaric conditions on liver monoamine oxidase activity in Komandor squid and mice]. / Vliianie giperbarii na aktivnost' monoaminoksidazy pecheni komandorskogo kal'mara i myshi.

Liver monoamineoxidase of Berryteuthis magister has been first studied for its activity and substrate specificity. Valid decrease of monoamineoxidase activity has been observed in the preparation obtained from the mouse liver by three studied substrates (serotonine, tyramine, benzylamine) as affected by high pressure (101 at; helioxygen mixture and hydrostatical conditions). At the same time, monoamineoxidase activity in the preparation isolated from Berryteuthis magister liver did not change under such conditions. Such stability of the liver enzyme of Berryteuthis magister dwelling under natural conditions under the effect of high pressure is treated from the viewpoint of biochemical adaptation.

[Effects of prolonged hyperbarism on lipid peroxidation and structural-functional state of erythrocytes]. / Vliianie dlitel'noi giperbarii na aktivnost' perekisnogo okisleniia lipidov i strukturno-funktsional'noe sostoianie éritrotsitov.

Prolonged helium-oxygen hyperbaric (pressure 3,6 MPa) increased diene conjugate and Schiff's base level in plasma and erythrocyte membranes of mice. In those conditions SOD and glucose 6-phosphate dehydrogenase activities were inhibited in erythrocytes. Lipid bilayer microviscosity and cholesterol content of erythrocyte membranes were increased.

[The water-salt metabolic state of guinea pigs after a prolonged stay at different temperatures of a hyperbaric environment]. / Sostoianie vodno-solevogo obmena u morskikh svinok posle dlitel'nogo prebyvaniia pri razlichnykh temperaturakh giperbaricheskoi sredy.

Guinea-pigs were exposed for 6-10 days to a helio-oxygen mixture with the pressure 6 x 10(5) and 36 x 10(5) Pa and temperature 30.5 degrees C to 34.5 degrees C. The concentration of cations was studied in the blood serum and cortex, outer medulla and papilla of the kidney. At the optimal temperature of the helio-oxygen mixture, the concentrations of sodium, potassium, calcium, magnesium and osmotically active substances did not differ from the control in the blood serum. In these conditions, the renal ability to create osmotic gradient does not change, i.e. the systems responsible for the permanence of the cation composition of internal milieu work in a sufficiently effective way and maintain a stable concentration of ions in the blood serum.

[The cytochrome P-450 content and catalytic activity in rat liver microsomes during hyperbaric oxygenation]. / Soderzhanie i kataliticheskaia aktivnost' tsitokhroma P-450 v mikrosomakh pecheni krys pri giperbaricheskoi oksigenatsii.

The effect of different conditions of hyperbaric oxygenation (HBO) on content and catalytic activity of cytochrome P-450 in rat liver cytochrome has been studied. The intensity of lipid peroxidation in microsomal membranes has been determined by the content of dien conjugates and Schiff's bases. The rate of amidopyrine demethylation has been shown not to change, but the rate of aniline hydroxylation decreases on 34, 57 and 64% under increase of oxygen pressure up to 0.3, 0.5 and 0.7 MPa correspondingly. The level of dien conjugates increase on 66-87% under all studied conditions of HBO. Cytochrome P-450 content decreases on 45% under the action of 0.7 MPa, but content of Schiff's bases increases on 210% as compared with control.