高溫刺激下點帶石斑魚稚魚(Epinephelus coioides)能量代謝途徑的探討

Abstract

環境中的緊迫因數會影響魚類正常的生理功能，在可忍受的範圍內，透過神經內分泌等生理過程，維持體內的恆定。能量的利用對生理的補償以及馴化過程扮演重要的角色。其中以主要的能量來源碳水化合物，在魚類遭受緊迫時，最值得探討。 馴化於25℃下的點帶石斑魚幼魚，分別投放至25℃、30℃、34℃、38℃水溫下進行刺激，探討其在高溫緊迫下的能量利用情形，包括溫度耐受性、耗氧量、24小時內的血液葡萄糖、乳酸以及碳水化合物相關的代謝酵素變動情形。耗氧量在初期的溫度刺激下，與處理溫度呈現正相關，隨溫度的升高而遞增，顯示高溫下增加的耗氧需求。血漿中的葡萄糖，在處理初期2小時內呈現急遽升高的趨勢，且與處理溫度亦有正相關，控制組則在2小時以後恢復，30℃組與34℃組則在6小時至24小時間維持較高的量，顯示體內能量來源需求的增加。血漿中乳酸的變動情形，在初期2小時亦有急遽升高的趨勢，且與處理溫度呈現正相關，顯示以無氧代謝進行醣解作用獲得能量增強，在6小時候均恢復至原來的水準。 與碳水化合物代謝相關的酵素，分別在四種組織，肌肉、肝臟、心臟、腦中測定其活性之時程變化，包括醣解作用中的Phosphofructokinase、Pyruvate kinase、Lactate dehydrogenase，醣質新生中的Pyruvate carboxylase、 Phosphoenolpyruvate carboxykinase、Fructose-l,6-diphosphatase，肝醣代謝酵素Glycogen synthase、Gyycogen phosphorylase,檸檬酸循環酵素Malate dehydrogenase、Citrate synthase，五碳醣代謝中的Glucose-6-phosphate dehydrogenase，以及Glycerol kinase。酵素活性的變動，反映出體內能量代謝的狀態。 在肝臟組織中，肝醣分解酵素活性的增加與血液葡萄糖含量呈現相關性，肝臟組織同時增加醣質新生與無氧代謝的能力，顯示在高溫刺激下，肝臟組織為主要能量提供的器官。肌肉組織亦顯示肝醣分解與無氧代謝的趨勢，在心臟組織則穩定進行有氧代謝外，在致死的刺激下亦有增強無氧代謝的趨勢，而腦組織同時具有增強有氧代謝及無氧代謝以因應高溫刺激下的能量需求。

Environmental stressors alter the normal physiological conditions of fishes.They are capable to compensate the nccessary physiological processes to maintain internal homeostasis through neuroendocrine processes within the tolerable range.Energy is essential for the physiological compensation and acclimation.Carbonhydrate,a main energy source in most organisms, should be highly concerned and addressed when fish are suffered from stresses. The groupers were acclimated at 25℃ for at least 4 weeks, and then transferred from 25℃ to 25,30,34 and 38℃,respectively.The thermal tolerence and the heat-shock responses of the oxygen consumption,plasma glucose and lactate in 24 he duration were systematically monitored.The oxygen consumption under short-term heat shock indicating an cnhanced aerobic properties of these fish with elevated temperatures. Plasma glucose were markedly elevated in the first 2 hr, and the trend of the increase are correlated with temperatures, The plasma glucose titers maintained at a higher level after 6 hours. A similar trend of the plasma lactate changes were also observed in the first 2 hr period, but the plasma lactate titers decreased thereafter and reached at the baseline level after 6 hr of heat exposure. Selected enzyme activities inmuscle, liver, heart and brain were assayed. Included are glycolytic enzymes (PFK., PK, LDH), gluconeogenic enzymes (PC, PEPCK, FDPase), glycogen metabolizing enzymes (glycogen synthase, phosphorylase), Krebs cycle enzymes (MDH, CS), and lipid metabolizing enzymes (G6PDH, glycerol kinase). The status of energy metabolism in vivo were implied from the enzyme activities assayed. The plasma glucose level was correlated with the glycogen phosphorylase in the liver of groupers. Both gluconcogenic and anaerobic capacity of the liver indicated that groupers liver is the main energy fuel supplying tissue when fish were suffer from heat stress. Muscle tissue also shown the trends of glycogen mobilization and anaerobic metabolism. The heart of groupers shows a stable aerobic capacity but increases anaerobic metabolism when the heat stress were lethal. Brain tissue has both increasing trends of aerobic and anaerobic metabolism indicated the highly energy demand of this tissue under heat stress.