Metabolic organization and effects of feeding on enzyme activities of the dogfish shark (Squalus acanthias) rectal gland
Metabolic organization and effects of feeding on enzyme activities of the dogfish shark (Squalus acanthias) rectal gland
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DOI：
10.1242/jeb.02329
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发表时间：
2006-08
影响因子：
2.8
通讯作者：
P. Walsh;M. Kajimura;T. Mommsen;C. Wood
中科院分区：
文献类型：
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作者：
P. Walsh;M. Kajimura;T. Mommsen;C. Wood
摘要为了研究板鳃鱼直肠腺的代谢平衡，我们进行了两条线的实验。首先，我们研究了饥饿后和6，20，30和48 h后喂养的角鲨，角鲨的几个组织中的几个代谢途径的血浆代谢产物和酶活性的影响。我们发现，与饥饿的角鲨相比，在6 h及以后血浆β-羟基丁酸盐快速且持续地降低了10倍，这表明该底物的使用上调，产量减少，或两者兼而有之。血浆乙酰乙酸水平保持不变，而6 h时血糖水平出现轻微和一过性降低。几种酶的活性在摄食后显示出大幅增加，包括直肠腺和肝脏中的β-羟基丁酸脱氢酶、直肠腺中的异柠檬酸脱氢酶、柠檬酸合成酶、乳酸脱氢酶、天冬氨酸氨基转移酶、丙氨酸氨基转移酶、谷氨酰胺合成酶和Na+/K+ ATP酶。在这些酶测量中还值得注意的是，一般而言，直肠腺中的活性水平总体较高。例如，三羧酸循环酶柠檬酸合酶的活性（超过30 U g-1）与其他高活性鱼类的肌肉活性相似。令人惊讶的是，乳酸脱氢酶活性的腺体也很高（超过150 U g-1），这表明无论是厌氧生产乳酸或使用乳酸作为有氧燃料的能力。鉴于这些有趣的观察结果，在研究的第二个方面，我们检查了几种代谢底物（单独和组合）支持直肠腺分泌氯的能力。在生理浓度下检测的底物（葡萄糖、β-羟基丁酸、乳酸、丙氨酸、乙酰乙酸和谷氨酸）中，仅葡萄糖可始终保持活性制剂。尽管β-羟基丁酸酯在与葡萄糖组合存在时可以增强腺体活性，但令人惊讶的是，当用作单独底物时，它不能维持氯化物分泌。我们的研究结果进行了讨论的背景下，在体内的作用的腺体和可能上调的酶活性的机制。
SUMMARY In order to investigate the metabolic poise of the elasmobranch rectal gland, we conducted two lines of experimentation. First, we examined the effects of feeding on plasma metabolites and enzyme activities from several metabolic pathways in several tissues of the dogfish shark, Squalus acanthias, after starvation and at 6, 20, 30 and 48 h post-feeding. We found a rapid and sustained ten-fold decrease in plasma β-hydroxybutyrate at 6 h and beyond compared with starved dogfish, suggesting an upregulation in the use of this substrate, a decrease in production, or both. Plasma acetoacetate levels remain unchanged, whereas there was a slight and transient decrease in plasma glucose levels at 6 h. Several enzymes showed a large increase in activity post-feeding, including β-hydroxybutyrate dehydrogenase in rectal gland and liver, and in rectal gland, isocitrate dehydrogenase, citrate synthase, lactate dehydrogenase, aspartate amino transferase, alanine amino transferase, glutamine synthetase and Na+/K+ ATPase. Also notable in these enzyme measurements was the overall high level of activity in the rectal gland in general. For example, activity of the Krebs' TCA cycle enzyme citrate synthase (over 30 U g-1) was similar to activities in muscle from other species of highly active fish. Surprisingly, lactate dehydrogenase activity in the gland was also high (over 150 U g-1), suggesting either an ability to produce lactate anaerobically or use lactate as an aerobic fuel. Given these interesting observations, in the second aspect of the study we examined the ability of several metabolic substrates (alone and in combination) to support chloride secretion by the rectal gland. Among the substrates tested at physiological concentrations (glucose, β-hydroxybutyrate, lactate, alanine, acetoacetate, and glutamate), only glucose could consistently maintain a viable preparation. Whereas β-hydroxybutyrate could enhance gland activity when presented in combination with glucose, surprisingly it could not sustain chloride secretion when used as a lone substrate. Our results are discussed in the context of the in vivo role of the gland and mechanisms of possible upregulation of enzyme activities.