Effects Of Acute Hypoxia On Lactate Transport And Metabolism Of Largemouth Bass (Micropterus Salmoides)

In order to reveal the effects of different degrees of acute hypoxia environment on the lactate transport and glucose metabolism of the largemouth bass,we set different degrees of acute hypoxia environment in the laboratory including control group(dissolved oxygen: 7 ±0.15 mg/L),moderate acute hypoxia(dissolved oxygen: 3.5 ± 0.12 mg/L)and acute hypoxia(dissolved oxygen: 1.2 ± 0.2 mg/L),and we analyzed physiological and biochemical parameters of the Largemouth bass(108.40 ± 2.88 g,17.06 ± 0.35 cm)at different points(0,4,8,12 and 24 h)and re-oxygenation(12 h hypoxia and 12 h re-oxygenation)at 20℃.1.Effects of different degrees of acute hypoxia stress on the RBCs in the Largemouth bassHypoxia induced the increase of the number of red blood cells through the HIF-1 αpathway to increase hypoxia tolerance.According to the analysis of the RBCs of the largemouth bass,the RBCs of the Largemouth bass in the 3.5 mg/L group and the 1.2 mg/L group was significantly increased after acute hypoxia stress.However,there were differences in the RBCs after different degrees of hypoxia treatment.Moreover,the 1.2 mg/L group rises earlier than the 3.5 mg/L group,and it gradually decreased to the level of the control group after 12 h re-oxygenation.The experiment shows that exposure duration to hypoxia and the oxygen concentration can regulate the increase of the number of red blood cells.2.Effects of different degrees of acute hypoxia stress on the glucose metabolism in the Largemouth bassThe metabolism of carbohydrates was altered under acute hypoxia stress.In the short term,liver glycogen was decomposed by the AMPK α and HIF-1 α pathways to increase blood glucose levels,and the glycolytic pathway was activated to maintain energy.The large amount of lactic acid produced by anaerobic metabolism was converted by LDH.The levels of blood glucose and blood lactic acid in 3.5 mg/L group and 1.2 mg/L group were significantly increased after acute hypoxia stress,and the blood glucose and blood lactic acid content in the1.2 mg/L group were much higher.The liver glycogen content decreased firstly and then increased with the decrease of DO.But the muscle glycogen content in the 1.2 mg/L group and the 3.5 mg/L group were no change during the whole hypoxia(p ﹥ 0.05).The activity of liver LDH increased first and then decreased,while heart LDH activity remained relatively stable during hypoxia and did not change significantly compared to the control group(p ﹥ 0.05).Different from the LDH activity of the heart,the LDH in brain increased first and then decreased.3.Effects of acute hypoxic stress on genes related to lactic acid transport of Largemouth bassThe experiment successfully cloned the CDS sequences of AMPK α,LDH a,MCT1 and MCT4.The results of tissue distribution showed that the gene were highest in the liver,heart,brain and gills.The results showed that the MCT1 gene was highly expressed only in the heart tissue,indicating that the heart could transport lactic acid into the cells under hypoxia environment.This would lead to the lactic acid content in heart was increase.At the same time,the expression levels of MCT4 and LDH genes in heart and brain tissue increased significantly in the later stage of hypoxia stress.This indicates that the capacity of lactic acid transport was different in tissues.Heart tissue may have potential pathways for transferring lactic acid in other tissue(such as brain)into cells for oxidative metabolism.Simultaneously,it could reduced lactic acid in other tissues to increase the tolerance of cells to hypoxia environments.