The effect of short-term hypoxia on the activity of oxidoreductases, malate dehydrogenase (MDH, 1.1.1.37) and lactate dehydrogenase (LDH, 1.1.1.27) responsible for urgent adaptation to oxygen deficiency, was studied in the brain and gills (first branchial arch) of the Black Sea scorpionfish Scorpaena porcus. The control group of fish was kept at 4.5–6.7 mg O2 L–1 (normoxia), experimental groups were exposed to 1.7–3.7 mg O2 L–1 (mild hypoxia) and 0.3–1.0 mg O2 L–1 (acute hypoxia); the exposure time was 90 min, water temperature 21–22°C. The dissolved oxygen level was reduced by saturating water with nitrogen. Hypoxia had no significant impact on the brain structures. Under acute hypoxia, MDH and LDH activities, the MDH/LDH index and ATP level in the forebrain, diencephalon and midbrain (FDMB), as well as in the medulla oblongata (MB), remained at the level of control values. Mild hypoxia caused a proportional rise in MDH and LDH activities and an increase in the ATP level in FDMB, most likely, due to a reduced demand for ATP in this brain region. This phenomenon is supposed to be based on the GABAergic mechanism of brain activity regulation, which is able to reduce energy demands of nervous tissue due to increasing the GABAA receptor density. The gills were distinguished by minimum MDH and LDH activities at the background of high MDH/LDH index values. Acute hypoxia led to decrease LDH activity and increase the MDH/LDH index in the gills, reflecting thereby a transition of this organ to an anaerobic operational mode. Under acute hypoxia, there was detected an increase in the relationship within the “MDH activity ↔ LDH activity” system in all types of tissues (r = 0.81–0.94, p < 0.05–0.01), which is typical of the species tolerant to oxygen deficiency. Apparently, this effect is based on MDH coupling with glycolytic substrates under conditions of acute oxygen deficiency, which rules out excessive lactate accumulation under metabolic depression.

中文翻译：

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短期缺氧条件下黑海鲣鱼脑和鳃中能量代谢酶的活性和ATP含量

在大脑和鳃（第一鳃）中研究了短期缺氧对氧化还原酶、苹果酸脱氢酶（MDH，1.1.1.37）和乳酸脱氢酶（LDH，1.1.1.27）的活性的影响，这些酶负责紧急适应缺氧arch) 的黑海蝎子鱼 Scorpaena porcus。对照组鱼保持4.5-6.7 mg O2 L-1（常氧），实验组暴露于1.7-3.7 mg O2 L-1（轻度缺氧）和0.3-1.0 mg O2 L-1（急性缺氧） ; 暴露时间为 90 分钟，水温 21-22°C。通过用氮气饱和水来降低溶解氧水平。缺氧对大脑结构没有显着影响。在急性缺氧条件下，MDH 和 LDH 活性、前脑、间脑和中脑 (FDMB) 以及延髓 (MB) 的 MDH/LDH 指数和 ATP 水平，保持在控制值水平。轻度缺氧导致 MDH 和 LDH 活性成比例增加，FDMB 中 ATP 水平增加，这很可能是由于该大脑区域对 ATP 的需求减少。这种现象被认为是基于大脑活动调节的 GABA 能机制，它能够由于增加 GABAA 受体密度而减少神经组织的能量需求。在高 MDH/LDH 指数值的背景下，鳃通过最小的 MDH 和 LDH 活性来区分。急性缺氧导致LDH活性降低并增加鳃中的MDH/LDH指数，从而反映该器官向厌氧操作模式的转变。在急性缺氧条件下，检测到所有类型组织中“MDH 活性↔ LDH 活性”系统内的关系增加（r = 0.81-0.94，p < 0.05–0.01)，这是耐缺氧物种的典型特征。显然，这种效应是基于 MDH 与急性缺氧条件下的糖酵解底物偶联，这排除了代谢抑制下乳酸过度积累。