氨和空气暴露对大鳞副泥鳅组织中谷氨酰胺含量的影响

为研究氨对大鳞副泥鳅(Paramisgurnus dabryanus)(体重18~25 g)生理指标的影响,将其暴露于30 mmol/L NH_4Cl溶液和空气中0 h,6 h,12 h,24 h,48 h,72 h,以研究体外和体内氨对其体组织中谷氨酰胺含量、谷氨酰胺合成酶和谷氨酸脱氢酶活性的影响。研究发现,氨和空气暴露下,随着暴露时间的延长,大鳞副泥鳅肝脏和肌肉组织中谷氨酰胺含量有明显累积的趋势,脑、肝脏和肠道组织中谷氨酰胺合成酶活性均显著上升。氨和空气暴露显著影响大鳞副泥鳅脑和肠道组织中谷氨酸脱氢酶活性,但对肝脏组织中谷氨酸脱氢酶活性并没有显著性影响。结果表明,大鳞副泥鳅可通过体组织中累积谷氨酰胺来应对体外或体内氨浓度的上升,氨暴露和空气暴露可刺激体内谷氨酰胺的合成,将氨转化为无毒性的谷氨酰胺。肠道中谷氨酸脱氢酶活性显著上升,可能在鱼类应对氨氮毒性中,肠道谷氨酸脱氢酶比谷氨酰胺合成酶有更重要的作用。而大鳞副泥鳅肝脏组织中谷氨酸脱氢酶活性并不受氨和空气暴露的影响,这可能是由于肝脏组织中转氨酶催化生成了足量的谷氨酸。

Changes to tissue glutamine content, glutamine synthetase, and glu tamate dehydrogenase activities during ammonia and aerial exposure in Chinese loach (Paramisgurnus dabryanus)

Chinese loaches (body weight:18-25 g) were exposed to 30 mmol/L NH4C1 solution and air (exposure time:0,6,12,24,48,72 h) to assess changes in tissue glutamine content,glutamine synthetase (GS) activity,and glutamate dehydrogenase (GDH) activity during ammonia loading and aerial exposure.Glutamine accumulation in liver and muscle,as well as GS activity in the brain,liver,and intestine,were observed with increasing duration of ammonia and aerial exposure.In all analyzed tissue except the liver,GDH activity was significantly affected by ammonia and aerial exposure.Our results suggested that Chinese loaches respond to internal ammonia increase through glutamine accumulation.Glutamine synthetase then stimulates the glutamine formation pathway and converts ammonia into non-toxic glutamine.The marked increase of GDH activity in the intestines demonstrated that intestinal GDH is more important than intestinal GS in the overall defense against ammonia toxicity.Across the exposure period,variation in liver GDH activity was not affected by ammonia and air,nor associated with a concomitant increase in GS activity and glutamine content that probably occurred due to efficient glutamine replenishment via transaminase action.