Veauvy Clémence M, McDonald M Danielle, Van Audekerke Johan, Vanhoutte Greet, Van Camp Nadja, Van der Linden Annemie, Walsh Patrick J
Division of Marine Biology and Fisheries, NIEHS Marine and Freshwater Biomedical Sciences Center, Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, Miami, FL 33149-1098, USA.
Aquat Toxicol. 2005 Aug 15;74(1):32-46. doi: 10.1016/j.aquatox.2005.05.003.
Laboratory rodents made hyperammonemic by infusing ammonia into the blood show symptoms of brain cell swelling and increased intracranial pressure. These symptoms could be caused in part by an increase in brain glutamine formed when brain glutamine synthetase (GS) naturally detoxifies ammonia to glutamine. Previous studies on the Gulf toadfish (Opsanus beta) demonstrated that it is resistant to high ammonia exposure (HAE) (96 h LC(50)=10mM) despite an increase in brain glutamine. This study attempts to resolve whether the resistance of O. beta is mediated by special handling of brain water in the face of changing glutamine concentrations. Methionine sulfoximine (MSO), an inhibitor of GS, was used to pharmacologically manipulate glutamine concentrations, and magnetic resonance imaging (MRI) was used to assess the status of brain water. Ammonia or MSO treatment did not substantially affect blood acid-base parameters. Exposure to 3.5mM ammonium chloride in seawater for 16 or 40 h resulted in a parallel increase in brain ammonia (3-fold) and glutamine (2-fold) and a decrease in brain glutamate (1.3-fold). Pre-treatment with MSO prevented ammonia-induced changes in glutamine and glutamate concentrations. HAE also induced an increase in plasma osmolality (by 7%) which was probably due to a disturbance of osmoregulatory processes but which did not result in broader whole body dehydration as indicated by muscle water analysis. The increase in brain glutamine was not associated with any changes in brain water in toadfish exposed to 3.5 mM ammonia for up to 40 h or even at 10, 20 and 30 mM ammonia consecutively and for one hour in each concentration. The lack of brain water accumulation implies that ammonia toxicity in toadfish appears to be via pathways other than cerebral swelling. Furthermore, toadfish pre-treated with MSO did not survive a normally sub-lethal exposure to 3.5 mM ammonia for 40 h. The enhancement of ammonia toxicity by MSO suggests that GS function is critical to ammonia tolerance in this species.
通过向血液中注入氨使实验用啮齿动物产生高氨血症，会出现脑细胞肿胀和颅内压升高的症状。这些症状可能部分是由于脑谷氨酰胺合成酶（GS）将氨自然解毒为谷氨酰胺时，脑内谷氨酰胺增加所致。先前对海湾蟾鱼（Opsanus beta）的研究表明，尽管脑内谷氨酰胺增加，但它对高氨暴露（HAE）具有抗性（96小时半数致死浓度（LC(50)）=10mM）。本研究试图解决在谷氨酰胺浓度变化的情况下，海湾蟾鱼的抗性是否由对脑内水分的特殊处理介导。蛋氨酸亚砜胺（MSO）是GS的抑制剂，用于通过药理学手段操纵谷氨酰胺浓度，磁共振成像（MRI）用于评估脑内水分状况。氨或MSO处理对血液酸碱参数没有实质性影响。在海水中暴露于3.5mM氯化铵16或40小时，导致脑内氨（增加3倍）和谷氨酰胺（增加2倍）平行增加，脑内谷氨酸减少（减少1.3倍）。MSO预处理可防止氨诱导的谷氨酰胺和谷氨酸浓度变化。高氨暴露还导致血浆渗透压升高（7%），这可能是由于渗透调节过程受到干扰，但肌肉水分分析表明并未导致更广泛的全身脱水。在暴露于高达40小时的3.5mM氨甚至连续暴露于10、20和30mM氨且每种浓度暴露1小时的海湾蟾鱼中，脑内谷氨酰胺的增加与脑内水分的任何变化均无关。脑内水分没有积累意味着海湾蟾鱼的氨毒性似乎是通过脑肿胀以外的途径产生的。此外，用MSO预处理的海湾蟾鱼在正常情况下亚致死剂量的3.5mM氨暴露40小时后未能存活。MSO增强氨毒性表明GS功能对该物种的氨耐受性至关重要。
