N tau-Methylimidazoleacetic acid, the histamine metabolite, and its isomer, N pi-methylimidazoleacetic acid, were demonstrated and measured in rat brain and in human cerebrospinal fluid, urine, and plasma by a gas chromatographic-mass spectrometric method that is simple and specific with a detection limit of about 7 pmol (i.e. 1 ng). The acids were separated in biological samples by ion exchange chromatography, derivatized as n-butyl esters with boron trifluoride-butanol, and extracted with chloroform. Complete chemical ionization mass spectra and mass ion abundance ratios established the identity of N tau - and N pi - methylimidazoleacetic acids in the biological extracts and of imidazoleacetic acid in urine, but not in cerebrospinal fluid, plasma, and brain. The methylimidazoleacetic acids as n-butyl esters were quantified by electron impact selected ion monitoring of m/e 95 esters at different retention times. 3-Pyridylacetic acid was used as an internal standard and monitored at m/e 93. The levels of N tau-methylimidazoleacetic acid and N pi-methylimidazoleacetic acid were, respectively (picomoles/g or picomoles/ml +/- S.E.), for brain, 373, 19 +/- 13.08 and 110.33 +/- 12.44; for cerebrospinal fluid, 22.77 +/- 2.15 and 80.76 +/- 18.92; and for plasma, 84.57 +/- 13.64 and 73.64 +/- 14.50. In urine, the respective levels were 20.75 +/- 1.30 and 73.02 +/- 38.22 nmol/mg of creatinine. The origin of N pi-methylimidazoleacetic acid is not certain.

中文翻译：

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脑和体液中甲基咪唑乙酸的存在和测量。

N tau-甲基咪唑乙酸，组胺代谢物及其异构体N pi-甲基咪唑乙酸通过简单而又特异的气相色谱-质谱法在大鼠脑以及人脑脊液，尿液和血浆中得到证实和测量检测极限约为7 pmol（即1 ng）。通过离子交换色谱分离生物样品中的酸，将其与三氟化硼-丁醇衍生为正丁酯，并用氯仿萃取。完整的化学电离质谱和质量离子丰度比确定了生物提取物中的N tau-和N pi-甲基咪唑乙酸的身份以及尿液中（而非脑脊液，血浆和脑中）的咪唑乙酸的身份。通过在不同保留时间对m / e 95酯进行电子碰撞选择离子监测，对作为正丁酯的甲基咪唑乙酸进行了定量。使用3-吡啶基乙酸作为内标，并在m / e 93处进行监测。Ntau-甲基咪唑乙酸和N pi-甲基咪唑乙酸的水平分别为（皮摩尔/克或皮摩尔/毫升+/- SE）。脑，373、19 +/- 13.08和110.33 +/- 12.44；对于脑脊液，22.77 +/- 2.15和80.76 +/- 18.92; 对于血浆，则为84.57 +/- 13.64和73.64 +/- 14.50。在尿液中，各自的水平为20.75 +/- 1.30和73.02 +/- 38.22 nmol / mg肌酐。N pi-甲基咪唑乙酸的来源尚不确定。对于大脑，N tau-甲基咪唑乙酸和N pi-甲基咪唑乙酸的水平分别为（皮摩尔/ g或皮摩尔/ ml +/- SE），分别为373、19 +/- 13.08和110.33 +/- 12.44；对于脑脊液，22.77 +/- 2.15和80.76 +/- 18.92; 对于血浆，则为84.57 +/- 13.64和73.64 +/- 14.50。在尿液中，各自的水平为20.75 +/- 1.30和73.02 +/- 38.22 nmol / mg肌酐。N pi-甲基咪唑乙酸的来源尚不确定。对于大脑，N tau-甲基咪唑乙酸和N pi-甲基咪唑乙酸的水平分别为（皮摩尔/ g或皮摩尔/ ml +/- SE），分别为373、19 +/- 13.08和110.33 +/- 12.44；对于脑脊液，22.77 +/- 2.15和80.76 +/- 18.92; 对于血浆，则为84.57 +/- 13.64和73.64 +/- 14.50。在尿液中，各自的水平为20.75 +/- 1.30和73.02 +/- 38.22 nmol / mg肌酐。N pi-甲基咪唑乙酸的来源尚不确定。