Effects Of Hypoxia On Respiratory Metabolism, Energy Metabolism And Antioxidant Capability Of Macrobrachium Nipponense

In this paper, the effects of hypoxia stress on respiratory metabolism energy metabolism and antioxidant capability of Macrobrachium nipponense were investigated, while the mechanism and the response mechanism of Macrobrachium nipponense were primarily discussed. Adult shrimps were exposed to hypoxia(2±0.2 mg/L,8 h), followed by reoxygena-tion (7±0.2 mg/L,2.5 h). The hepatopancreas and muscle tissues of M.nipponense were extracted at 0 h,2 h,4 h,6 h, and 8 h of hypoxia periods and 8.5 h,9.5 h and 10.5 h of reoxygenation periods respectively, then the physiological and biochemical parameters of these tissues were analyzed. The results are as follows:1 The effect of hypoxia on respiratory metabolism of M.nipponense. With the duration of hypoxia exposure, activities of cytochrome coxidase(CCO) and succinate dehydrogenase (SDH) of M.nipponense as aerobic metabolic enzymes in the hepatopancreas and muscle tissues were significantly lower compared with the control group (normoxia level,7±0.2 mg/L,10.5 h) (P<0.05). Meanwhile, fumarate reductase (FRD) and lactate dehydrogenase (LDH) activities of anaerobic metabolic enzymes were significantly higher compared with the control group (P<0.05). During reoxygenation, CCO, SDH,FRD and LDH activities gradually returned to the control level. The results demonstrated that aerobic metabolism weakened, while anaerobic metabolism which was catalyzed by FRD and anaerobic glycolysis strengthened when M.nipponense were exposed to hypoxia, during reoxygenation, respiratory metabolism of M.nipponens recovered the former level.2 The effect of hypoxia on energy metabolism of M.nipponense.With the duration of hypoxia exposure, glycogen concentration and arginine kinase(AK) activities of hepatopan-creas and muscle tissues significantly reduced compared with the control group (P<0.05), meanwhile lactate concentration of muscles significantly increased (P< 0.05). During reoxygenation, glycogen concentration and AK activities were remained significantly lower compared with the control group (P<0.05), while lacate concentration of muscles gradually returned to the control level, but there was no effect on the lactate concentration of the hepatopancreas exposure to hypoxia stress and reoxygenation. The results indicated that whether exposure to hypoxia or reoxygenation, there were other two metabolic pathways: glycolysis and phosphoarginie metabolism provided part of energy for M.nipponense, except for aerobic metabolism.3 The effect of hypoxia on antioxidant capability of M.nipponense. The superoxide dismutase(SOD) activities significantly decreased(P<0.05), catalase(CAT), glutathione S-transferase(GST), antisuperoxide anion(anti-O2-·) materials activities and total antioxidant capability(T-AOC) significantly increased(P<0.05). During reoxygenation, SOD activities enchanced and activities of CAT, GST, anti-O2-·materials and T-AOC decreased, eventually all of them gradually returned to the control level. In addition, there was no effect in the concentration of malondialdehyde(MDA) during hypoxia period, but MDA concentration significantly increased during reoxygenation. The result indicated that whether exposed to hypoxia or reoxygenation affected antioxidant capability of M.nipponens, especially during reoxygenation, shrimp were subjected to oxidative stress which induced increase of the peroxidation concentration.4 Enzyme activities and metabolic substance of respiratory metabolism, the energy metabolism and other metabolic processes showed differnces between the hepatopancreas and muscle tissues. SDH,CCO, FRD, LDH, SOD,CAT,GST and anti-O2-·materials activities, T-AOC, glycogen and MDA concentration of hepatopancreas significantly higher than these of the muscles (P<0.05), but the lactate concentration and AK activities of muscles significantly higher than the hepatopancreas tissue's. The results demonstrated that different function which hepatopancreas and muscle tissues work resulted in differnces of enzyme activities and metabolic substance concentration of respiratory metabolism, energy metabolism and oxidative balance between the hepatopancreas and muscle tissues.In summary, hypoxia stress greatly influenced on the physiological and biochemical responses of M.nipponens. The results demonstrated that the level of aerobic metabolism weakened and anaerobic metabolism ste ngthened, while excessive consumption of glycogen and phosphoarginine which were storaged as energy substance, and strong responses of antioxidant capability might be a emergency strategy to adapt hypoxia environment, also might be one of reasons that M.nipponense is much sensitive to hypoxia.