Successive extreme climatic events lead to immediate, large-scale, and diverse responses from fish in the Arctic

The warming trend of the Arctic is punctuated by several record-breaking warm years with very low sea ice concentrations. The nature and reversibility of marine ecosystem responses to these multiple extreme climatic events (ECEs) are poorly understood. Here, we investigate the ecological signatures of three successive bottom temperature maxima concomitant with surface ECEs between 2004 and 2017 in the Barents Sea across spatial and organizational scales. We observed community-level redistributions of fish concurrent with ECEs at the scale of the whole Barents Sea. Three groups, characterized by different sets of traits describing their capacity to cope with short-term perturbations, reacted with different timing and intensity to each ECE. Arctic species co-occurred more frequently with large predators and incoming boreal taxa during ECEs, potentially affecting food web structures and functional diversity, accelerating the impacts of long-term climate change. On the species level, responses were highly diversified, with different ECEs impacting different species, and species responses (expansion, geographical shift) varying from one ECE to another, despite the environmental perturbations being similar. Past ECEs impacts, with potential legacy effects, lagged responses, thresholds, and interactions with the underlying warming pressure, could constantly set up new initial conditions that drive the unique ecological signature of each ECE. These results highlight the complexity of ecological reactions to multiple ECEs and give prominence to several sources of process uncertainty in the predictions of climate change impact and risk for ecosystem management. Long-term monitoring and studies to characterize the vertical extent of each ECE are necessary to statistically link demersal species and environmental spatial-temporal patterns. In the future, regular monitoring will be crucial to detect early signals of change and understand the determinism of ECEs, but we need to adapt our models and management to better integrate risk and stochasticity from the complex impacts of global change.

Distribution and ecology of polar cod (Boreogadus saida) in the eastern Barents Sea: A review of historical literature

The polar cod (Boreogadus saida) has a circumpolar distribution and is the most abundant planktivorous fish in the Arctic. Declining sea-ice coverage impacts polar cod directly and also facilitates expansion of human activities in the region leading to increasing anthropogenic pressures on biota. Here we summarize current data and knowledge on polar cod from the Russian sector of the Barents Sea and discuss knowledge needs for the management of polar cod under changing environmental conditions and anthropogenic impacts. We review 36 Russian historical (1935 - 2020) sources of data and knowledge largely unknown to western researchers, in addition to sources already published in the English language. This effort allowed for digitalization and visualization of 69 separate datasets on polar cod ecology, including maturation, fertility, feeding intensity, diet, lipid content, length-weight relationships and seasonal variation in larval size. Our review suggests that polar cod abundances are particularly large in the eastern Barents Sea and adjacent waters. Here, we identify and discuss key knowledge gaps. The review of polar cod in the eastern Barents Sea revealed 1) major variation in the timing and area of polar cod spawning, 2) uncertainty as to what degree the polar cod is dependent on sea ice, 3) deficient knowledge of juvenile (e.g., 0-group) distributions, particularly in the north-eastern Barents Sea, 4) deficient knowledge of the species' genetic structure and spatio-temporal distributions, and 5) insufficient understanding as to whether ongoing environmental change may induce phenological changes affecting the availability of potential food items for polar cod larvae and their match in space and time. Filling these knowledge gaps would provide an important step towards the reliable knowledge base needed in order to perform well-founded management and impact assessment under environmental changes and increasing anthropogenic impacts.

Resource-driven colonization by cod in a high Arctic food web

Climate change is commonly associated with many species redistributions and the influence of other factors may be marginalized, especially in the rapidly warming Arctic.The Barents Sea, a high latitude large marine ecosystem in the Northeast Atlantic has experienced above-average temperatures since the mid-2000s with divergent bottom temperature trends at subregional scales.Concurrently, the Barents Sea stock of Atlantic cod Gadus morhua, one of the most important commercial fish stocks in the world, increased following a large reduction in fishing pressure and expanded north of 80°N.We examined the influence of food availability and temperature on cod expansion using a comprehensive data set on cod stomach fullness stratified by subregions characterized by divergent temperature trends. We then tested whether food availability, as indexed by cod stomach fullness, played a role in cod expansion in subregions that were warming, cooling, or showed no trend.The greatest increase in cod occupancy occurred in three northern subregions with contrasting temperature trends. Cod apparently benefited from initial high food availability in these regions that previously had few large-bodied fish predators.The stomach fullness in the northern subregions declined rapidly after a few years of high cod abundance, suggesting that the arrival of cod caused a top-down effect on the prey base. Prolonged cod residency in the northern Barents Sea is, therefore, not a certainty.

The rise of a marine generalist predator and the fall of beta diversity

Determining the importance of physical and biological drivers in shaping biodiversity in diverse ecosystems remains a global challenge. Advancements have been made towards this end in large marine ecosystems with several studies suggesting environmental forcing as the primary driver. However, both empirical and theoretical studies point to additional drivers of changes in diversity involving trophic interactions and, in particular, predation. Moreover, a more integrated but less common approach to the assessment of biodiversity changes involves analyses of spatial β diversity, whereas most studies to date assess only changes in species richness (α diversity). Recent research has established that when cod, a dominant generalist predator, was overfished and collapsed in a northwest Atlantic food web, spatial β diversity increased; that is, the spatial structure of the fish assemblage became increasingly heterogeneous. If cod were to recover, would this situation be reversible, given the inherent complexity and non-linear dynamics that typify such systems? A dramatic increase of cod in an ecologically similar large marine ecosystem may provide an answer. Here we show that spatial β diversity of fish assemblages in the Barents Sea decreased with increasing cod abundance, while decadal scale changes in temperature did not play a significant role. These findings indicate a reversibility of the fish assemblage structure in response to changing levels of an apex predator and highlight the frequently overlooked importance of trophic interactions in determining large-scale biodiversity patterns. As increased cod abundance was largely driven by changes in fisheries management, our study also shows that management policies and practices, particularly those involving apex predators, can have a strong effect in shaping spatial diversity patterns, and one should not restrict the focus to effects of climate change alone.

Functional roles and redundancy of demersal Barents Sea fish: Ecological implications of environmental change

When facing environmental change and intensified anthropogenic impact on marine ecosystems, extensive knowledge of how these systems are functioning is required in order to manage them properly. However, in high-latitude ecosystems, where climate change is expected to have substantial ecological impact, the ecosystem functions of biological species have received little attention, partly due to the limited biological knowledge of Arctic species. Functional traits address the ecosystem functions of member species, allowing the functionality of communities to be characterised and the degree of functional redundancy to be assessed. Ecosystems with higher functional redundancy are expected to be less affected by species loss, and therefore less sensitive to disturbance. Here we highlight and compare typical functional characteristics of Arctic and boreal fish in the Barents Sea and address the consequences of a community-wide reorganization driven by climate warming on functional redundancy and characterization. Based on trait and fish community composition data, we assessed functional redundancy of the Barents Sea fish community for the period 2004-2012, a period during which this northern region was characterized by rapidly warming water masses and declining sea ice coverage. We identified six functional groups, with distinct spatial distributions, that collectively provide a functional characterization of Barents Sea fish. The functional groups displayed different prevalence in boreal and Arctic water masses. Some functional groups displayed a spatial expansion towards the northeast during the study period, whereas other groups showed a general decline in functional redundancy. Presently, the observed patterns of functional redundancy would seem to provide sufficient scope for buffering against local loss in functional diversity only for the more speciose functional groups. Furthermore, the observed functional reconfiguration may affect future ecosystem functioning in the area. In a period of rapid environmental change, monitoring programs integrating functional traits will help inform management on ecosystem functioning and vulnerability.

Climate change alters the structure of arctic marine food webs due to poleward shifts of boreal generalists

Climate-driven poleward shifts, leading to changes in species composition and relative abundances, have been recently documented in the Arctic. Among the fastest moving species are boreal generalist fish which are expected to affect arctic marine food web structure and ecosystem functioning substantially. Here, we address structural changes at the food web level induced by poleward shifts via topological network analysis of highly resolved boreal and arctic food webs of the Barents Sea. We detected considerable differences in structural properties and link configuration between the boreal and the arctic food webs, the latter being more modular and less connected. We found that a main characteristic of the boreal fish moving poleward into the arctic region of the Barents Sea is high generalism, a property that increases connectance and reduces modularity in the arctic marine food web. Our results reveal that habitats form natural boundaries for food web modules, and that generalists play an important functional role in coupling pelagic and benthic modules. We posit that these habitat couplers have the potential to promote the transfer of energy and matter between habitats, but also the spread of pertubations, thereby changing arctic marine food web structure considerably with implications for ecosystem dynamics and functioning.

A trans-Atlantic examination of haddock Melanogrammus aeglefinus food habits

The food habits of Melanogrammus aeglefinus were explored and contrasted across multiple north-eastern and north-western Atlantic Ocean ecosystems, using databases that span multiple decades. The results show that among all ecosystems, echinoderms are a consistent part of M. aeglefinus diet, but patterns emerge regarding where and when M. aeglefinus primarily eat fishes v. echinoderms. Melanogrammus aeglefinus does not regularly exhibit the increase in piscivory with ontogeny that other gadoids often show, and in several ecosystems there is a lower occurrence of piscivory. There is an apparent inverse relationship between the consumption of fishes and echinoderms in M. aeglefinus over time, where certain years show high levels of one prey item and low levels of the other. This apparent binary choice can be viewed as part of a gradient of prey options, contingent upon a suite of factors external to M. aeglefinus dynamics. The energetic consequences of this prey choice are discussed, noting that in some instances it may not be a choice at all.

Demersal fish assemblages and spatial diversity patterns in the Arctic-Atlantic transition zone in the Barents Sea

Direct and indirect effects of global warming are expected to be pronounced and fast in the Arctic, impacting terrestrial, freshwater and marine ecosystems. The Barents Sea is a high latitude shelf Sea and a boundary area between arctic and boreal faunas. These faunas are likely to respond differently to changes in climate. In addition, the Barents Sea is highly impacted by fisheries and other human activities. This strong human presence places great demands on scientific investigation and advisory capacity. In order to identify basic community structures against which future climate related or other human induced changes could be evaluated, we analyzed species composition and diversity of demersal fish in the Barents Sea. We found six main assemblages that were separated along depth and temperature gradients. There are indications that climate driven changes have already taken place, since boreal species were found in large parts of the Barents Sea shelf, including also the northern Arctic area. When modelling diversity as a function of depth and temperature, we found that two of the assemblages in the eastern Barents Sea showed lower diversity than expected from their depth and temperature. This is probably caused by low habitat complexity and the distance to the pool of boreal species in the western Barents Sea. In contrast coastal assemblages in south western Barents Sea and along Novaya Zemlya archipelago in the Eastern Barents Sea can be described as diversity "hotspots"; the South-western area had high density of species, abundance and biomass, and here some species have their northern distribution limit, whereas the Novaya Zemlya area has unique fauna of Arctic, coastal demersal fish. (see Information S1 for abstract in Russian).

[Cholesterol esterification in tissues and change in the apoprotein spectrum in rat blood under the effect of auto-oxidized cholesterol]

Influence of autooxidized cholesterol (Ch) products on accumulation of cholesterol esters (ChE) in liver and aorta tissues as well as alteration of the apolipoprotein spectrum in low density and very low density (LDL and VLDL) lipoproteins in blood plasma was studied in rats treated with purified Ch (ChP-rats) and with oxidized Ch containing 5% 25-hydroxyCh and 3% 7-ketoCh (ChO-rats). Increase of ChE content in liver tissue of ChO-rats resulted in two-fold activation of acyl-CoA-cholesterol-O-acyltransferase (ACAT) in liver microsomes as compared with the enzymatic activity rate in ChP-rats. As shown by polyacrylamide gel electrophoresis content of apoE in VLDL and LDL of ChO-rats was 1,5-fold higher as compared with that of ChP-rats. Content of apoIV was increased in LDL and VLDL of ChP-rats as compared with controls; this effect was not observed in ChO-rats. LDL and VLDL from ChO-rats stimulated incorporation of 14C-oleate into ChE of cultivated macrophages. Increase in content of ChE found in aorta of ChO-rats appears to occur due to activation of Ch esterification. Intensification of ChE synthesis in tissues and alterations in the spectrum of LDL and VLDL apolipoproteins caused by oxidized products of cholesterol may be one of the mechanisms involved in atherogenesis.

[Effects of tocopherol on functional reserves of phagocytes]

The addition of alpha-tocopherol into rats died (4 mg a day during 7 days) brings a twofold increase in tocopherol content in blood plasma and 1,3 fold increase in peritoneal macrophages. Viscosity of membrane lipids of macrophages was decreased. Control and experimental macrophages had identical activity of oxygen-dependent processes and ability for cholesterol esterification.

[Esterification of cholesterol oxidation products and their effect on the rate of cholesterol esterification in macrophages]

Effects of cholesterol (CH) autooxidation products on incorporation of 14C-oleate into cholesteryl esters (CE) and their possible esterification were studied in cultivated mice peritoneal macrophages (MPM). 25 Mg/ml of purified CH and 25 Mg/ml of autooxidized CH stimulated (4- and 17-fold, respectively) the cholesterol esterification in MPM. In presence of 4 Mg/ml 25-hydroxy CH or the mixture of 4 Mg/ml 7 alpha-, 7 beta-hydroxy CH and 7-keto CH incorporation of oleate into cellular CE was increased 20- and 4-fold, respectively. 4 Mg/ml concentration of cholestane-3 beta, 5 alpha, 6 beta-friol caused no effects. Mono- and diesters of 14C-hydroxy CH were found after 8 hrs incubation of the steroid with MPM. Incorporation of 14C-25 hydroxy CH into its esters occurred at the rate, which exceeded 6-7-fold the 14C-CH incorporation into CE. Esterification of 7 alpha-, 7 beta-hydroxyCH and 7-ketoCH was studied, 0.52% label of the total cell sterols radioactivity was detected in the fraction of nonpolar steroids. 14C-cholestane-3 beta,5 alpha,6 beta-triol was not esterified in MPM. The stimulating effects of 25-hydroxyCH on oleate incorporation into CE and its esterification in MPM were inhibited in presence of 10 Mg/ml progesterone, an inhibitor of acyl-CoA:cholesterol acyltransferase activity. Induction of CE formation in MPM by means of choltransferase activity. Induction of CE formation in MPM by means of cholesterol oxidation products may be responsible for development of foam cells, while esterification of polar steroids in cells appears to be of importance in decrease of their toxic and metabolic effects.

[Effect of the monooxygenase activity inhibitor ketoconazole on cholesterol esterification in mouse peritoneal macrophages]

In order to determine the feasible role of monooxygenases in regulation of the macrophage acyl-CoA: cholesterol acyltransferase (ACAT) activity, the effects of ketoconazole on the activities of benz(a)pyrene hydroxylase and ACAT as well as on the [14C]oleate incorporation into cholesterol esters in cultured mouse peritoneal macrophages (MPM) were studied. Ketoconazole (0.5-50 M) inhibited the benz(a)pyrene hydroxylase activity but increased the free cholesterol (FC) level in MPM cultured with an acetylated low density lipoprotein (acetyl-LDL). An addition of ketoconazole (1-50 M) eliminated the increase in the rate of FC esterification after incubation of MPM with acetyl-LDL (but not with 25-hydroxycholesterol). In contrast, progesterone, an ACAT activity inhibitor, used at 5-30 M diminished the rate of FC esterification, when MPM were incubated with acetyl-LDL of 25-hydroxycholesterol. Ketoconazole provoked a dose-dependent decrease of the [3H]FC incorporation into macrophage polar oxysteroids. The data obtained suggest that the ketoconazole (1-30 M) effect on FC esterification in MPM cultured with acetyl-LDL is determined by its inhibiting monooxygenases, which produce oxidized forms of FC that are potential activators of ACAT.

[The effect of progesterone on metabolism of cholesterol esters in macrophages cultured with acetylated low density lipoproteins]

Effect of progesterone on esterification of free cholesterol, on content of free cholesterol and its esters was studied in rat macrophages, cultivated in presence of acetyl-derivatives of low density lipoproteins (Ac-LDL), as well as on mobilization of cholesterol from macrophages. Progesterone at a dose of 0.5-10 micrograms per I ml of cultivating medium caused dose-dependent inhibition of I-14C-oleate incorporation into cholesterol esters of macrophages cultivated with Ac-LDL (50 micrograms of protein/ml). In the medium free of LDL progesterone caused an increase of cholesterol in macrophages by 45%, while addition of 100 micrograms/ml LDL led to a decrease of free cholesterol by 20% of the initial level. If macrophages pre-enriched with 4-C14-cholesterol were cultivated in LDL containing medium, progesterone increased the 4-14C-cholesterol liberation into medium and decreased the cholesterol content in macrophages. Under conditions of macrophages incubation in the LDL-free medium, progesterone increased the free cholesterol content in these cells but did not affect the 4-14C-cholesterol liberation into medium. The data obtained suggest that the progesterone-induced inhibition of free cholesterol esterification may increase its mobilization from macrophages only if the LDL acceptor function is unaltered.

[The effect of dibutyryl cAMP, verapamil and adrenaline on cholesterol mobilization from macrophages]

The capacity of dibutyryladenosine-3':5'-cyclic phosphate (dibutyryl cAMP), verapamil and epinephrine to modulate cholesterol (CH) excretion was studied in the stored (4-14C)-CH rat macrophages. The experiments indicated that in the absence of high density lipoproteins (HDL) the addition of dibutyryl cAMP (0.2 mmol), verapamil (0.05 mmol), epinephrine (0.05 mmol) in cultured medium did not influence the excretion of the stored (4-14C)-CH from macrophages during 4, 8 and 18 hours. The addition of the drugs in the presence of HDL resulted in an increase in the excretion of (4-14C)-CH from macrophages during incubation. The data indicate that the drugs which increase the cellular concentration of cAMP can induce the mobilization of CH from macrophages in the presence of acceptors of CH.

[Skin cholesterol level and its correlation with the lipid indicators of the blood serum in healthy persons and in patients with ischemic heart disease]

Skin free and esterified cholesterol in the forearm and serum lipid levels were examined in 42 male coronary patients and 46 normal male subjects. Irrespective of the type of dislipoproteinemia or normolipidemia, total cholesterol and its free fraction appear to be significantly increased in coronary patients, as compared to normal subjects. There were no significant correlations between the examined skin and serum parameters, either in coronary patients, or in the controls. Possible use of skin cholesterol measurement in the diagnosis of lipid disturbances leading to atherosclerosis is discussed.

[Lecithin-cholesterol-acyltransferase activity in chronic liver diseases]

Activity of lecithin-cholesterol-acyl transferase (LCAT) was distinctly decreased in chronic impairments of liver tissue, especially under conditions of liver cirrhosis and hepatocellular cancer. After treatment with "essentiale forte" the enzymatic activity was elevated only in the patients with chronic hepatitis. The LCAT activity correlated with content of albumins, gamma-globulins and the data of thymol test. Estimation of the LCAT activity might serve as a diagnostic test in chronic liver tissue diseases.

[Cholesterol esterase activity in the rat aorta and liver after stimulation and blockade of beta-adrenergic receptors]

Activities of lysosomal and cytoplasmic cholesterol esterases and cholesterol content in rat blood serum, liver tissue and aorta were studied after administration of ephedrine and propranolol. The ephedrine-induced lipolytic effect was fully inhibited by propranolol. The correlation between stimulation of beta-adrenergic receptors and activation of lipolytic enzymes was found.

[Prevention of damages to the microsomal monooxygenases in thermal ischemia of the liver by the separate and combined use of alpha-tocopherol, lidocaine and kontrikal]

It was found in experiments on the in vitro model of rat liver ischemia that ischemia initiates membrane lipid peroxidation and proteolysis leading to damage of monooxygenase enzyme systems of microsomes. Preventive administration of alpha-tocopherol, lidocaine, contrykal and their combinations revealed the optimal protective effect of the combined administration of alpha-tocopherol with lidocaine and alpha-tocopherol with contrykal as compared to their separate use on the functional activity of microsomal monooxygenases at thermal ischemia of the liver. A combined approach to prevention of impairment of the liver function at its ischemia was recommended.

[Effect of 17 alpha-ethinyl estradiol on the blood serum lipid indices of rats]

The administration of 17-ethinyl estradiol (0.25 mg/kg) to male Wistar rats caused on the 3rd day a decrease of the levels of free and esterified cholesterol, blood serum triglycerides and also a reduction of the content of esterified cholesterol with respect to total cholesterol while the lecithin-cholesterol-acyltransferase activity appeared to be unchanged. The effect of ethinyl estradiol on blood lipid parameters against the background of lipemia induced by triton WR 1339 was reduced.

[Changes in the activity of enzymes of cholesterol esters synthesis and hydrolysis in rat adrenals after treatment with 17 alpha-ethinyl estradiol]

A study was made of the effect of hypocholesterolemia induced by 3-day administration of 17 alpha-ethinyl estradiol on the activity of lysosomal and cytoplasmatic cholesterol esterases, acyl-CoA: cholesterol acyltransferase and on the free and esterified cholesterol concentrations in the rat adrenals. A decrease in the content of esterified cholesterol in the adrenal tissue was accompanied by a decrease in the activity of acyl-CoA: cholesterol acyltransferase and by an increase in the activity of lysosomal cholesterol esterase. The activity of cytoplasmatic cholesterol esterase was not changed significantly. The data obtained were discussed with relation to the synthesis of steroid hormones in the rat adrenals.

[Activity of key enzymes of cholesterol biotransformation and lipid content in the liver, aorta, adrenals and blood of rats exposed to chloroquine]

Intraperitoneal administration of chloroquine (50 mg/kg, 7 days) to rats was followed by the increase of cholesterol, its esters, triglycerides and phospholipids levels in tissues, the decrease of lysosomal cholesterol esterase and acyl-koA-cholesterol acyl transferase activity in the liver and the enhancement of the non-sedimentable activity of acid phosphatase and beta-galactosidase. At concentration range of 3.5 to 140 mM the drug inhibited the activity of cholesterol esterase in the rat liver lysosome fraction.

[Activity of cholesterol metabolism enzymes and lipid levels in the rat liver, aorta, adrenals and serum after exposure to triton WR 1339]

Injection of Triton WR 1339 into Wistar rats caused a marked increase in contents of free and ester-bound cholesterol, triglycerides, phospholipids and free fatty acids in tissues and a decrease in the activity of lecithin: cholesterol acyltransferase in blood. An increase in concentration of cholesterol esters in tissues was due to a decrease in activity of lysosomal cholesteryl esterase in vivo and in vitro and to an increase in non-sedimentable activities of acid phosphatase, beta-galactosidase and cholesteryl esterase. The decrease in proteolytic degradation of cholesterol esters was accompanied by an increase in the activity of tissue cytoplasmic cholesteryl esterase and by a decrease in activity of acyl-CoA: cholesterol O-acyltransferase in liver tissue.

[Mechanisms of the damage to the liver monooxygenase systems in thermal ischemia]

It was shown in experiments in vitro that thermal ischemia of liver tissue leads to disorders in the function of membrane-bound microsomal monooxygenases. Disorders in the structural organization of membranes were also expressed in the inhibition of reactions of ascorbate-depending and fermentative peroxide oxidation of lipids and labilization of lysosomal membranes. Faults in the rate of amidopyrine n-demethylation and aniline n-hydroxylation correlate with the intensification of spontaneous peroxidation of lipids and activation of proteolytic processes in ischemia. The obtained data permitted to ground the approach to pharmacological prophylaxis of ischemic damages of liver microsomal monooxygenases.

[Structural-functional aspects of the postischemic recovery of the hepatocyte endoplasmic network in rats]

The experiments on rats have shown that total hepatic ischemia reduces the content of microsomal cytochromes P-450 and b5 and causes amidopyrine and aniline disturbances over a 2-3-week post-ischemic period. The analysis of hepatocyte ultrastructure has revealed the interdependence of structural and functional changes in endoplasmic reticulum during recovery period. The damage of monooxygenase inducibility correlated with stable decline in the number of fixed ribosomes in post-ischemic period.

[The use of unsaturated phosphatidylcholines for determining the cholesterol esterase activity of biological matter]

A relatively simple method for preparation of a new substrate used in highly effective estimation of cholesterol esterase activity is described. Emulsion containing cholesterol I-14C oleate and unsaturated phosphatidyl cholines (70% linolic and 30% linolenic acids) was stabilized within three months.

[Changes in the lipid levels of the liver, plasma, aorta and cholesterol esterase activity of the rat liver during exposure to tetrachloromethane]

Content of cholesterol esters was increased 2.3-fold, triglycerides--4.7-fold, phospholipids--1.5-fold in liver tissue of CCl4-treated rats. The increase in the content of cholesterol esters and triglycerides correlated with a decrease in activity of lysosomal cholesterol esterase from liver tissue. After CCl4 intoxication content of free cholesterol was decreased 2.1-fold, free fatty acids--2-fold, phospholipids--2.3-fold, triglycerides--1.75-fold in blood. In aorta an increase in content of cholesterol esters and triglycerides was found to be 2-fold as well as activation of the cytosolic cholesterol esterase was noted. The data obtained suggest that intoxication with CCl4 affected the accumulation of cholesterol esters in the arterial wall.

[Effect of membranotropic agents on lysosomal acid cholesterol esterase of the rat liver]

An activity of acid cholesterol esterase was estimated in homogenate of liver tissue, lysosomal fraction and delipidated lysosomes using labelled cholesterol oleate contained in phospholipid liposomes. Taurocholate at the concentration of 2.6 mM increased the enzymatic activity but the mixture of taurocholate and Triton X-100 inhibited the enzyme. After addition of cholesterol the enzymatic activity and the activating effect of taurocholate were distinctly decreased. Alterations in the activity of acid cholesterol esterase and in the intalysosmal accumulation of cholesterol and of its esters may occur due to modifications of the substrate physical structure.

[Effect of changes in the oxygen level on cholesterol esterase activity of the liver of intact rats and rats subjected to chronic hypoxia]

Alterations in activity of cholesterol esterases from lysosomal, microsomal and cytoplasmic cell fractions of rat liver tissue were studied under conditions of acute and chronic hypoxia and hyperoxia. Activity of the membrane-bound lysosomal and microsomal cholesterol esterases was decreased but the cytoplasmic enzyme was activated in acute hypoxia and hyperoxia. These data suggest that the enzymes, responsible for alterations in the ratio free cholesterol/cholesterol esters in cells, are dependent on the level of oxygen consumption.

[Characteristics of the ischemic disorders of xenobiotic metabolism in the liver of rats in the early and late stages of recovery]

It has been demonstrated in rat experiments that total ischemia of the liver leads to disorders of the metabolism of xenobiotics and endogenous substrates. Upset hexenal metabolism manifests in the prolongation of the hexenal-induced sleep and hexenal concentration elevation in blood plasma for 18 days of the postischemic period. Following exposure to ischemia liver microsomes show a decrease in the rate of amidopyrine, aniline and hydrocortisone hydroxylation. Hydrocortisone metabolism returns to normal by day 14, that of amidopyrine by day 21 of the postischemic period. Aniline metabolism gets disturbed to a greater degree, remaining 33.4% lower by day 21. It has been shown that the inducibility of microsomal monooxygenases is substantially restricted by days 7 and 14 of the postischemic period.

[Metabolism of xenobiotics in the liver in acute hypoxia of intact mice and mice adapted to oxygen deficiency]

Experiments on white mice were made to study the effect of acute hypoxia in intact and hypoxia adapted animals on the function of liver hydroxylases. It was shown that acute hypoxia (vacuum 462 Pa, exposure 120 min) leads to a decrease in the rate of amidopyrine demethylation by liver microsomal enzymes. Preadaptation to hypoxia reduces the depth of microsomal hydroxylation inhibition in response to hypoxia. Variation in the constant of substrate binding with the enzymatic complex plays in important role in the mechanism of microsomal oxidation inhibition in the liver under hypoxia. The concentration of the hemoproteins P = 450 and b5 does not undergo any substantial changes.

[Stabilization of biological membranes with various acetylene amines]

In experiments with mitochondrial membranes and membranes of the endoplasmatic reticulum of the rats' liver the membrane-stabilizing action of a number of unsaturated amines was evaluated. The acetylene compounds studied reduced the extent of the membranes damage following UV-irradiation, treatment with detergents and their incubation in a hypoosmotic medium. Such an action displayed gutimine and sovcaine. Hydrated compounds, analogues of acetylene amines are devoid of the ability to raise the resistance of the cellular organoids membranes to damaging factors

[Respiration toxins as inhibitors of ion transport, supported by ATP hydrolysis, in mitochondria]

Effect of respiration toxins is studied on some properties of mitochondrial membranes and functions connected with ion transport for the expence of ATP energy. The combination of three respiration inhibitors (cyanide, antimycin and rotenone) was shown to develope the following effects: 1) the inhibition of K+ accumulation by mitochondria at the presence of ATP and valinomycin; 2) the decrease in acidification of non-mitochondrial space, accompanying to the K+ transport; 3) the activation of latent mitochondrial ATPase; 4) the inhibition of DNP-stimulated ATPase; 5) the inhibition of mitochondria swelling, caused by K+, Ca2+, or dimethyldibenzylammonium (DDA+) at the presence of ATP+phopshate (or acetate); 6) the stimulation of passive mitochondria swelling in 0.1 MNH4NO3; 7) the inhibition of ATP-induced contraction of mitochondria, swelling in NH4NO3. The data obtained are discussed in a wiev of the conception, which suggests that the attaching of inhibitors to respiration enzymes changes the configuration of the latters, thus disturbing natural structural bond of these enzymes with other protein components of the membrane. The latter can result in the impair of electroisolating membrane properties, in the increase of its conductivity for H+ and other ions, and in the decrease of Vm values of some enzymatic reaction, which are not directly connected with the respiration chain (such as ATPase reaction).