Huntington Medical Research Institutes, Pasadena, California, USA.
J Magn Reson Imaging. 2014 Feb;39(2):398-401. doi: 10.1002/jmri.24166. Epub 2013 Jun 3.
To use (13) C magnetic resonance spectroscopy (MRS) and (31) P MRS to develop a direct assay for regional [HCO3-] in the human brain and to define brain pH and physiological response of [HCO3-] to fasting.
Seven healthy subjects underwent MRS examinations on a 1.5T MRI scanner. Subjects were well fed with repeated examinations performed after 4 and 12 hours of fasting. Proton noise decoupling (13) C MRS were acquired using pulse and acquired acquisition while (31) P MRS were acquired using a 2D chemical shift imaging method with relaxation time (TR) of 2 seconds.
Fasting brain bicarbonate concentrations (6.7 ± 2.5 mM for 12-hour fasting, P = 0.002 and 8.3 ± 2.1 mM for 4-hour fasting, P = 0.015) are significantly reduced compared to fed state (11.6 ± 1.3 mM). However, no significant difference in brain pH was observed, confirming the critical role of pCO2 in intracerebral pH homeostasis.
We demonstrated that the intracellular HCO3- in human brain is readily modified by diet but appears to have no measurable effect on cerebral pH. Natural abundance (13) C can provide useful information relevant to human brain pH homeostasis by providing information for HCO3-.
利用 (13) C 磁共振波谱 (MRS) 和 (31) P MRS 开发一种直接检测人脑局部 [HCO3-] 的方法，并定义脑 pH 值以及 [HCO3-] 对禁食的生理反应。
7 名健康受试者在 1.5T MRI 扫描仪上进行了 MRS 检查。受试者在充分进食后，分别进行 4 小时和 12 小时的禁食，重复进行检查。使用脉冲和采集获取质子去耦 (13) C MRS，同时使用二维化学位移成像方法（弛豫时间 (TR) 为 2 秒）获取 (31) P MRS。
与进食状态相比，禁食时脑碳酸氢盐浓度（12 小时禁食时为 6.7 ± 2.5 mM，P = 0.002，4 小时禁食时为 8.3 ± 2.1 mM，P = 0.015）显著降低。然而，脑 pH 值没有明显差异，这证实了 pCO2 在脑内 pH 稳态中的关键作用。
我们证明了人类大脑中的细胞内 HCO3- 可通过饮食轻易改变，但似乎对脑 pH 值没有可测量的影响。天然丰度 (13) C 可通过提供 HCO3- 相关信息，为研究人类大脑 pH 稳态提供有用信息。
