Volume 55, Nº 5 (2019)
- Ano: 2019
- Artigos: 13
- URL: https://journals.rcsi.science/0022-0930/issue/view/9709
Reviews
The Problem of Assessing Individual Sensitivity and Tolerance to Hypoxia in Animals and Humans
Resumo
The problems of individual sensitivity and tolerance of an organism to environmental exposures refer to most fundamental challenges of physiology being tackled for a long time. Meanwhile, different authors may be at variance in interpreting the terms “sensitivity” and “tolerance”. This review summarizes literature data on the issues of interpreting and assessing sensitivity and tolerance to hypoxia. A special focus is on those studies which compare the initial individual response of an organism to hypoxia and its viability at subsequent stages of hypoxic and other extreme exposures. When resolving these issues, it is necessary to allow for the existence of two opposite life support strategies, active and passive. The first strategy takes advantage of early detecting detrimental exposures and mobilizing energy resources aimed at their avoidance. The second strategy implies saving (instead of mobilizing) energy resources due to hierarchical functional activity limitation (downregulation) which allows an organism to survive exposure as long as possible at relatively low sensitivity and reactivity. The existence of the second strategy disallows unambiguous interpretation of results of hypoxic tolerance assessment based on analyzing functional disorders, such as mental and physical performance decrement and locomotor incoordination, which arise under hypoxic exposures.
Report on the Relative Affinity Constant (M) of Hemoglobin for Carbon Monoxide in the Animal World: A Comparative Review with a Meta-Analysis Based on a Systematic Review
Resumo
The Haldane M-value is the ratio of half-saturation pressures for O2 and CO (PO2/PCO) and is a key value of physiological and pathological models exploring CO metabolism or exposure to CO. Nevertheless, the M-values obtained from different studies and different species appear to be inconsistent. A better estimation of M-values and a consideration of interspecies variation will ensure the accuracy of CO study results and allow reliable models to be constructed. We performed a systematic review and meta-analysis in order to determine and compare M-values according to species and experimental conditions. We used electronic libraries (PubMed/Embase/JSTORE) from 1895 to January 2016. For each article, we collected the following parameters: species, age, temperature, pH, atmospheric pressure, concentration of 2,3-diphosphoglycerate (2,3-DPG) or methemoglobin, and type of hemoglobin. The systematic review found 25 articles addressing the M constant, including 135 with individual data and 51 with mean values concerning mammals, laboratory animals, fish, fetal hemoglobin and invertebrates. M-values at a physiological temperature and pH were assessed only for adult (137 [119–153]) and fetal (135 [112–168]) sheep, dogs (215 [193–218]), mice (194 [118–278]) and rats (191 [177–200]). A correlation between M-values and temperature was confirmed for sheep and horses. A correlation between M-values and pH could not be inferred because there was a lack of data. M-values varied according to species. Only the influence of temperature was confirmed. A formal measurement of the M constant in the given experimental conditions should be performed for each animal model study of CO. Further homogeneous studies are necessary to compare the M-values of different animals.
Comparative and Ontogenic Biochemistry
Adaptive Mechanisms of Baroreflectory Regulation of the Cardiovascular System in Extreme Hyperoxia
Resumo
The cardiovascular system of vertebrates, including humans, is well known to respond to hyperoxia by vasoconstriction, bradycardia and decreased contractility of the left heart ventricle. We hypothesized that all of these responses are components of the baroreflex that regulates blood pressure and circulation in hyperoxia. To test this hypothesis, we carried out experiments on awake rats in which the dynamics of arterial blood pressure, organ blood flow (brain, kidney, lower limbs) and ECG was tracked in response to oxygen breathing at 1, 3 and 5 ATA. The afferent and efferent baroreflex pathways were studied using denervation of the carotid baroreceptors and transection of the aortic depressor nerves and vagus nerve. The baroreflex effectiveness was assessed using phenylephrine injections or spontaneous changes in blood pressure. To activate the GABAergic system, nipecotic acid was injected into the lateral ventricle of the brain. Our studies demonstrated the presence of all the baroreflex components in hyperoxia which were triggered by a sharp rise in blood pressure due to systemic vasoconstriction. Hyperoxic vasoconstriction, in turn, arose due to endothelium-derived nitric oxide (NO) which binds to superoxide anions followed by a loss of the vasodilator component of vascular tone. Aortic and carotid sinus baroreceptors with ascending nerve fibers were identified as an afferent component of the hyperoxic baroreflex. Bradycardia and a decrease in cardiac output, resulting from baroreflex activation by hyperoxia, are actualized via efferent sympathetic and parasympathetic pathways. At 1 and 3 ATA the baroreflex effectiveness increased compared to atmospheric air breathing, but extreme hyperoxia (5 ATA) suppressed the baroreflex mechanism. Activation of the GABAergic system in the cerebral cortex by nipecotic acid prevented the loss of the hyperoxic baroreflex. In hyperoxia, the baroreflex mechanism realizes adaptive responses of the cardiovascular system aimed at restraining the delivery of excess oxygen to an organism and mitigates activation of the sympathetic nervous system.
Interspecies Peculiarities of Some Enzyme Activities in the Gonads of Black Sea Fish
Resumo
Significant interspecies differences were established in activities of aminotransferases, alanine aminotransferase (ALT, EC 2.6.1.2) and aspartate aminotransferase (AST, EC 2.6.1.1), and alkaline phosphatase (ALP, EC 3.1.3.1) in the gonads of seven Black Sea fish species during spawning and non-spawning seasons. In most species, ALT and AST activities were higher in the non-spawning phase compared to the spawning one, while ALP activity demonstrated an opposite trend. The peak enzymatic activities were found in the gonads of the whiting, probably due to its spawning in the winter season. No significant differences were revealed between the test parameters in animals of different ecological groups. ALT, AST and ALP activities in fish gonads can be used as convenient and efficient markers to explore both the peculiarities of the gonadogenesis at different stages of the reproductive cycle and the ability of different fish species to adapt to unfavorable environments, including those caused by anthropogenic pollution.
Morphological Basics for Evolution of Functions
The Role of Alpha-Tocopherol and Cycloferon in the Regulation of Apoptosis in Neurons of the Hypothalamic Suprachiasmatic Nucleus and Pinealocytes during Stress and Aging
Resumo
The suprachiasmatic nucleus (SCN) of the hypothalamus and the pineal gland (epiphysis) play an important role not only in the regulation of circadian rhythms but also in the implementation of adaptive responses, including those to various stress factors. Age-related morphofunctional changes in these brain structures, including those associated with increased oxidative stress, exert a significant effect on the organism as a whole. The aim of this work was to explore the dynamics and mechanism of apoptosis in pinealocytes and SCN neurosecretory cells as well as to determine the possibilities of pharmacological correcting this process by an antioxidant alpha-tocopherol and an immunomodulator cycloferon under physiological and immobilization stress conditions in young (2–4-month-old) and aged (30-month-old) Wistar rats. The preparations were administered perorally once a day for 14 days. While the apoptosis level increased with age both in the SCN and the pineal gland, administration of alpha-tocopherol, cycloferon and their combination led to abate this process. It was shown that stress-induced apoptosis in the SCN and the pineal gland proceeds via the p53-dependent pathway, while administration of alpha-tocopherol acetate, cycloferon and their combination decreases the apoptosis level in pinealocytes, suppressing p53 expression both in young and aged animals. In the SCN, no relationship was found between apoptosis and p53 expression levels after administration of the above preparations during stress, suggesting the involvement of different mechanisms.
Problem Papers
Two-Level Organization of Thermogenesis in Adipose Tissue: a Morphofunctional Hypothesis
Resumo
A new hypothesis based on structural and molecular heterogeneity of thermogenic adipocytes suggests that regulated thermogenesis in mammalian adipose tissues involves two structural-functional levels. The first level comprises typical brown fat and beige adipocytes of subcutaneous white fat depots. Being a part of the functional thermoregulatory system, this level of heat production is controlled by the appropriate hypothalamic centers. The second level is represented by visceral beige adipocytes with a relatively low total thermogenic capacity which provide a fine local adjustment of thermal optima for cell renewal processes. This level is regulated mainly by the local auto- and paracrine mechanisms.
Principles of Evolution of the Excretory Organs and the System of Homeostasis
Resumo
The function of the excretory organs in metazoan invertebrates and vertebrates is aimed at maintaining homeostasis. Two patterns of the morpho-functional organization of these organs can be distinguished: I—a combination of ultrafiltration and subsequent reabsorption with partial secretion of substances, or II—only a secretion of molecules of a certain type. Here we substantiate the principle according to which in the type I organs the key role of the proximal tubule is to reabsorb fluid, which is ideal in terms of its solute composition and concentration, and to secrete a number of organic acids and bases, while the distal tubule is responsible for adjusting the composition of inorganic substances. Everything what does not meet these criteria is to be excreted. The type II organs (salt glands, aglomerular kidneys) are inherent to those animals whose kidneys do not ensure osmoregulation. During evolution, the mammalian kidney developed the mechanism which regulates the redistribution of fluid within the nephron: altered reabsorption of ions and water in the proximal segment can cause an influx of some additional fluid to the distal segment where the regulatory systems adjust the amount of reabsorbed substances. The central tendency in the evolution of the kidney in vertebrates, including humans, is to increase the rates of glomerular filtration and proximal reabsorption. A similarity between molecular mechanisms of transmembrane and transepithelial transport of substances has been revealed in the evolution of excretory organs, with distinctions concerning mainly the structure of the regulatory molecules and the intensity of urine formation.
Short Communications
Superoxide Dismutase Activity in Phylogenetically Heterogeneous Regions of the Rat Brain during Repetitive Sessions of Hyperbaric Oxygenation
Resumo
Our study addresses the effect of repetitive sessions of hyperbaric oxygenation (HBO) (2 ATA, 50 minutes, 1 session a day) on superoxide dismutase (SOD) activity as assayed by a chemiluminescent method in the phylogenetically heterogeneous brain structures (brain stem, cerebellum, cerebral hemispheres) of white rats. A study of intact animals (series 1, control) revealed no statistically significant differences in SOD activity between these structures. One HBO session (series 2) stimulated SOD activity in all the brain structures: in the hemispheres, cerebellum and stem by 41, 31 and 66% vs. control, respectively (p < 0.05). After five HBO sessions (series 3), the SOD response intensity in the brain stem exceeded that in the other structures (p < 0.05) and increased by 187% vs. control (p < 0.001). Further continuation of oxygenation up to ten sessions (series 4) was accompanied by a normalization of SOD activity. After eighteen HBO sessions (series 5), the SOD activity level in the cerebellum and cerebral hemispheres somewhat increased compared to the 10th HBO session, although remained closer to the values of the control group than to those of the brain stem. In the brain stem, the SOD activity level exceeded that in intact rats by 46% (p < 0.05).