title: Impact of fasting on human brain acid-base homeostasis using natural abundance (13) C and (31) P MRS.
abstract: OBJECTIVE
  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.
  
  
  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 (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.
  
  
  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.
  
  
  CONCLUSIONS
  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-.
authors.affiliation: Huntington Medical Research Institutes, Pasadena, California, USA.
authors.forename: Napapon
authors.initials: N
authors.lastname: Sailasuta
authors.forename: Kent C
authors.initials: KC
authors.lastname: Harris
authors.forename: Thao T
authors.initials: TT
authors.lastname: Tran
authors.forename: Osama
authors.initials: O
authors.lastname: Abulseoud
authors.forename: Brian D
authors.initials: BD
authors.lastname: Ross
mesh_terms: D000136:Acid-Base Equilibrium / Q000502:physiology*; D000328:Adult; D001639:Bicarbonates / Q000378:metabolism*; D001921:Brain / Q000502:physiology*; D001923:Brain Chemistry; D002247:Carbon Isotopes / Q000493:pharmacokinetics; D005215:Fasting / Q000502:physiology*; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D010759:Phosphorus Isotopes / Q000493:pharmacokinetics; D012016:Reference Values; D014018:Tissue Distribution
chemical_list: D001639:Bicarbonates; D002247:Carbon Isotopes; D010759:Phosphorus Isotopes
keywords: 13C MRS; 31P MRS; Henderson-Hasselbalch equation; brain pH