Nuclear magnetic resonance study on the evaluation of energy metabolism in the brain in vivo-A case of rat brain intoxicated with methymercury-

尽管人们对有机汞的毒性进行了大量的研究，但其毒性的分子和细胞机制仍不清楚。在本研究中，我们专注于甲基汞对脑能量代谢的影响，并进行了核磁共振研究，旨在评估在体内脑的氧化能力。取得了如下结果：1.方法：1.采用甲基汞5 mg Hg/kg体重/d连续灌胃12天的方法建立大鼠甲基汞中毒模型.利用表面线圈探针和手术相结合的方法，成功地进行了磷-31核磁共振测量，观察了脑内高能磷代谢产物，避免了周围肌肉和皮肤的信号污染.在甲基汞中毒的脑中，ATP的稳态浓度保持正常，但磷酸肌酸（PCr）的稳态浓度从正常浓度5.48 μ mol ^^降至4.78 μ mol <-1>^<-1>^。根据13 P NMR饱和转移测量，正常和中毒脑中的ATP周转率均为0.22 μ mol/g/<-1>sec/g<-1><31>。假设由ADP控制氧化磷酸化反应的Michaelis-Menten方程，从稳态PCr水平和ATP周转率评价体内脑中的氧化磷酸化能力。结果表明，中毒脑组织的氧化能力比正常脑组织降低约15%.我们也正在发展一种大鼠脑质子定位光谱技术，以观察未磷酸化的代谢物。

In spite of great efforts to elucidate the toxicity of organic mercury, the molecular and cellular mechanism of the toxicity remains still unclear. In the present study we focused on the effect of methylmercury on energy metabolism in brain, and conducted an NMR investigation aiming at evaluation of oxidative capacity in the brain in vivo. The following results have been obtained.1. A rat model of methylmercury poisoning was established by oral administration of 5mg Hg/kg body weight methylmercury daily for 12 days.2. A phosphorus-31 NMR measurements were successfully carried out to observe high energy phosphorus metabolites from the brain avoiding signal contamination from the surrounding muscles and skins by a combination of a surface coil probe and a surgical operation.3. In the methylmercury poisoned brain the steady state concentration of ATP was maintained normal, but that of phosphocreatine (PCr) was reduced to 4.78 mumolg^<-1> compared with the normal concentration of 5.48mumolg^<-1>.4. An ATP turnover rate both in the normal and poisoned brain was 0.22 mumolg^<-1> sec^<-1> from the ^<31>P NMR saturation transfer measurement.5. Oxidative phosphorylation capacity in in vivo brain was evaluated from the steady state PCr level and the ATP turnover rate assuming a Michaelis-Menten equation controlled by ADP on the oxidative phosphorylation reaction. The result demonstrated that the oxidative capacity in the poisoned brain was approximately 15% reduced compared with the normal brain.6. We are also developing a technique of proton localization spectroscopy for rat brain to observe metabolites which are not phosphorylated.