Impact of fasting on human brain acid‐base homeostasis using natural abundance 13C and 31P MRS

Purpose To use 13C magnetic resonance spectroscopy (MRS) and 31P 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. Materials and Methods 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 13C MRS were acquired using pulse and acquired acquisition while 31P MRS were acquired using a 2D chemical shift imaging method with relaxation time (TR) of 2 seconds. Results 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. Conclusion 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 13C can provide useful information relevant to human brain pH homeostasis by providing information for HCO3−. J. Magn. Reson. Imaging 2014;39:398–401. © 2013 Wiley Periodicals, Inc.