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Biomedical subjects

A A Zhukov

Publications and source records attributed to A A Zhukov.

15 recordsLinked to original sources
PubMed2006

Structural transformations in sympathetic ganglia and the thoracic part of the vagus nerve in conditions of gravitational overloading.

The aim of the present work was to undertake a complex of studies of structural transformations in the anterior thoracic ganglia of the sympathetic trunk and the thoracic part of the vagus nerve after acute and chronic gravitational overloading (GOL). Studies were performed on 28 white mongrel male rats aged 8-21 weeks. Animals of series I (acute GOL) were rotated in a centrifuge on one day (three rotation sessions with two 20-min breaks, giving a total rotation time of 31 min). Animals of series II (chronic GOL) were rotated in an alternating two-week regime for 13 weeks (total rotation time 20 h 9 min). Rotation was performed in the craniocaudal direction with overloads of 4-6 g. Intact rats served as controls. Histological, electron microscopic, and morphometric analyses were performed. Acute GOL produced mainly reversible reactive changes in the anterior thoracic nodes of the sympathetic trunk and thoracic part of the vagus nerve, probably induced by unusual combinations of afferent spike activity of unusual strength, this probably being one of the causes of impairments seen after rotation. Chronic GOL was followed by the development of mainly destructive and compensatory-adaptive processes, characterized by the destruction of mitochondrial cristae, vacuolization of neuron cytoplasm, and degradation of interneuronal synapses. These changes were probably due to the development of hypoxia, which leads to interneuronal synaptic blockade in sympathetic ganglia. These structural transformations demonstrate the involvement of both the sympathetic and parasympathetic compartments in responses to acute and chronic GOL, providing evidence of the generalization of adaptive processes in the autonomic nervous system.

Animals↗
PubMed2005

[Structural modifications of the thoracic region of vagus and sympathetic trunk ganglia after exposure to gravitational overloads].

The aim of this work was the complex study of structural modifications in the anterior thoracic ganglia of the sympathetic trunk and in thoracic region of vagus after acute and chronic exposure to gravitational overloads (GO). The study was carried out in 28 albino outbred male rats aged 8-21 weeks. Animals of group I (acute exposure) were rotated in the centrifuge during one day (3 rotations with 2 20-min breaks; total exposure duration was equal to 31 min. Animals of group II (chronic exposure) were treated intermittently during 2-weeks-long periods for 13 weeks; total exposure duration was equal to 20 hours 9 min. Gravitation was applied in cranio-caudal direction with the overload of 4-6 gravitational units. Intact rats served as a control. Material was studied using histological, electron microscopic and morphometric methods. The study of the sympathetic trunk and thoracic ganglia following acute GO have revealed mainly the reactive and reversible changes, probably caused by the appearance of an afferent impulsation of unusual intensity and combination, which is one of the reasons of the disturbances, observed after rotation. Following chronic GO, destructive and compensatory-adaptive changes prevailed; these were characterized by the mitochondrial cristae destruction, vacuolization of neuronal cytoplasm, destruction of interneuronal synapses. These changes, were probably, the result of hypoxia leading to the development of interneuronal synaptic block in sympathetic ganglia. The structural modifications described are indicative of the involvement of both sympathetic and parasympathetic parts of the autonomic nervous system in the response to acute and chronic GO, suggesting the generalization of the adaptation processes in the autonomic nervous system after GO.

Animals↗
PubMed2004

Qutrit state engineering with biphotons.

The novel experimental realization of three-level optical quantum systems is presented. We use the polarization state of biphotons to generate a specific sequence of states that are used in the extended version of four-state QKD protocol quantum key distribution protocol. We experimentally verify the orthogonality of the basic states and demonstrate the ability to easily switch between them. The tomography procedure is employed to reconstruct the density matrices of generated states.

Journal Article↗
PubMed2003

Microfabricated adhesive mimicking gecko foot-hair.

The amazing climbing ability of geckos has attracted the interest of philosophers and scientists alike for centuries. However, only in the past few years has progress been made in understanding the mechanism behind this ability, which relies on submicrometre keratin hairs covering the soles of geckos. Each hair produces a miniscule force approximately 10(-7) N (due to van der Waals and/or capillary interactions) but millions of hairs acting together create a formidable adhesion of approximately 10 N x cm(-2): sufficient to keep geckos firmly on their feet, even when upside down on a glass ceiling. It is very tempting to create a new type of adhesive by mimicking the gecko mechanism. Here we report on a prototype of such 'gecko tape' made by microfabrication of dense arrays of flexible plastic pillars, the geometry of which is optimized to ensure their collective adhesion. Our approach shows a way to manufacture self-cleaning, re-attachable dry adhesives, although problems related to their durability and mass production are yet to be resolved.

Adhesives↗
PubMed2001

History effects and phase diagram near the lower critical point in YBa2Cu3O7 single crystals.

Using a sensitive torque magnetometer we have studied magnetization curves for untwinned overdoped YBa2Cu3O7 single crystals in fields of up to 28 T. We demonstrate the existence of history effects below the lower critical point and provide a full demarcation of the Bragg-glass phase. A pronounced symmetry is observed in the behavior of the phase lines, irreversible magnetization, and value of the magnetization jump near both critical points.

Journal Article↗
PubMed1991

Cytochrome P-450 spin state and leakiness of the monooxygenase pathway.

1. The monooxygenase and oxidase activities of liver microsomes from phenobarbital (PB)-treated rabbits were investigated for their dependence on the high spin shift (delta alpha) of the ferric cytochrome P-450 induced by a series of benzphetamine analogues. 2. The spin shift activity of the substrate determines, via the first electron transfer kinetics, the steady-state level of the reaction intermediate oxycytochrome P-450. Correlation of the amount or oxycytochrome P-450 with delta alpha can be experimentally proved. 3. The spin-state-dependent formation of oxycytochrome P-450 regulates quantitatively the rates of NADPH oxidation and substrate N-demethylation. Both activities correlate with delta alpha. Oxycytochrome P-450 is substrate-stabilized towards decay with the formation of O2- which, upon dismutation, gives rise to H2O2. 4. The ratio of N-demethylase to NADPH oxidase activity (coupling ratio) also increases with the spin shift, delta alpha. Concomitantly, the proportion of NADPH accounted for by H2O2 and H2O formation via two- and four-electron reduction of dioxygen decreases. This indicates that the substrate-induced structural changes in the enzyme active centre which give rise to spin transition may likewise modify the coupling properties. 5. Perfluorinated compounds, which fail to undergo monooxygenation, fall in line with the benzphetamine derivatives with respect to the dependence of NADPH oxidation rate and steady-state oxycytochrome P-450 level on delta alpha. The increased oxidase activity results mostly in H2O formation. 6. The leakiness of the PB-induced monooxygenase pathway in the biotransformation of oxygen in the presence of the benzphetamines and perfluorinated compounds does not result in marked increases in H2O2 formation. Therefore, the increase of NADPH oxidase activity by these substrates does not significantly enhance H2O2-mediated oxygen tissue toxicity.

Animals↗
PubMed1987

[Effect of monooxygenase reactions catalyzed by cytochrome P-450 on the microsomal membrane].

Hydroxylation of dimethylaniline in rabbit liver microsomes is accompanied by inactivation of cytochrome P-450 and the formation of products inhibiting the catalytic activity of non-inactivated cytochrome P-450. Other enzymes and electron carriers of microsomal membrane (cytochrome b5, NADH-ferricyanide reductase, NADPH-cytochrome c and NADPH-cytochrome P-450 reductases) as well as glucose-6-phosphatase were not inactivated in the course of the monooxygenase reactions. Phospholipids and microsomal membrane proteins were also unaffected thereby. Consequently, the changes in the microsomal membrane during cytochrome P-450 dependent monooxygenase system functioning are confined to the inactivation of cytochrome P-450.

Aniline Compounds↗
PubMed1985

[Stoichiometry of microsomal oxidation reactions. Distribution of redox-equivalents in monooxygenase and oxidase reactions catalyzed by cytochrome P-450].

The stoichiometry of NADPH oxidation in rabbit liver microsomes was studied. It was shown that in uncoupled reactions cytochrome P-450, besides O2- generation catalyzes direct two- and four-electron reduction of O2 to produce H2O2 and water, respectively. With an increase in pH and ionic strength, the amount of O2 reduced via an one-electron route increases at the expense of the two-electron reaction. In parallel, with a rise in pH the steady-state concentration of the oxy-complex of cytochrome P-450 increases, while the synergism of NADPH and NADH action in the H2O2 formation reaction is replaced by competition. The four-electron reduction is markedly accelerated and becomes the main pathway of O2 reduction in the presence of a pseudo-substrate--perfluorohexane. Treatment of rabbit with phenobarbital, which induces the cytochrome P-450 isozyme specific to benzphetamine results in a 2-fold increase in the degree of coupling of NADPH and benzphetamine oxidation. The experimental results suggest that the ratio of reactions of one- and two-electron reduction of O2 is controlled by the ratio of rates of one- and two-electron reduction of cytochrome P-450. In the presence of pseudo-substrates cytochrome P-450 acts predominantly as a four-electron oxidase; one of possible reasons for the uncoupling of microsomal monooxygenase reactions is the multiplicity of cytochrome P-450 isozymes.

Aniline Hydroxylase↗
PubMedDate not supplied

[Hyperbaric oxygenation in the combined treatment of acute kidney failure].

The paper presents the review of the treatment performed in 183 patients with acute renal failure caused by trauma, myorenal syndrome, surgical, obstetric and urological lesions. All the patients underwent hemodialysis. The majority of the patients manifested hypoxia due to pulmonary edema and abnormal central and visceral hemodynamics, anemia resultant from blood loss and suppression of hemopoiesis, impairment of tissue oxidation-reduction enzymes by uremic toxins. Hemodialysis aggravated hypoxia. A direct relationship existed between arterial hypoxemia and the degree of metabolic acidosis, electrolyte alterations and residual diuresis in oligoanuric stage of acute renal failure. The treatment of 48 relevant patients involved 5-10 sessions of hyperbaric oxygenation (1.5-2.2 atm for 60-90 min). The session usually followed hemodialysis. The response was achieved in arterial hypoxemia, central hemodynamics, peripheral blood, water-electrolyte balance, acid-base equilibrium, uremic intoxication. The frequency of hemodynamic reactions during hemodialysis and pyoseptic complications induced by uremia reduced as well as the need in urgent hemodialysis. The introduction of hyperbaric oxygenation diminished the lethality by 29%.

Acute Kidney Injury↗