title: Cerebral (31)P magnetic resonance spectroscopy and systemic acid-base balance during hypoxia in fetal sheep.
abstract: The purpose of this study was to investigate cerebral energy metabolism and acid-base homeostasis during impaired oxygen supply in fetal sheep. Systemic acid-base balance was correlated with the sequence in changes of cerebral phosphorus metabolite ratios and intracellular pH. Phosphorus magnetic resonance spectra were obtained from the brain of six fetal sheep simultaneously with repeated measurements of fetal arterial oxygen saturation and acid-base balance. Fetal hypoxia was induced by gradually reducing the oxygen supply to the anesthetized pregnant ewe to establish an intended arterial pH of 7.00 or lower. The ratio of phosphocreatine to inorganic phosphate decreased from 1.08 +/- 0.10 (SD) during the control period to 0.77 +/- 0.29 at an arterial pH between 7.20 and 7.25. The inorganic phosphate level became significantly increased at an arterial pH between 7.10 and 7.15 compared with control values. With ongoing arterial acidosis, cerebral intracellular pH decreased linearly with the arterial pH. At an arterial pH of 7.00, cerebral intracellular pH was decreased from 7.18 +/- 0.03 to 6.71 +/- 0.28, and phosphocreatine and nucleoside triphosphates levels were decreased significantly. In fetal sheep brain, cerebral oxidative phosphorylation (ratio of phosphocreatine to inorganic phosphate) is already affected at a mild arterial acidosis. At an arterial pH of 7.00 or lower, nucleoside triphosphates disappeared, which almost inevitably was followed by death in fetal sheep.
authors.affiliation: Department of Obstetrics and Gynecology, University Medical Centre St Radboud, 6500 HB Nijmegen, The Netherlands.
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Van Cappellen Van Walsum
authors.forename: Mark
authors.initials: M
authors.lastname: Rijpkema
authors.forename: Arend
authors.initials: A
authors.lastname: Heerschap
authors.forename: Berend
authors.initials: B
authors.lastname: Oeseburg
authors.forename: Jan G
authors.initials: JG
authors.lastname: Nijhuis
authors.forename: Henk W
authors.initials: HW
authors.lastname: Jongsma
mesh_terms: D000136:Acid-Base Equilibrium; D000818:Animals; D001921:Brain / Q000196:embryology / Q000378:metabolism*; D001923:Brain Chemistry; D005260:Female; D005333:Fetus / Q000502:physiology*; D006706:Homeostasis; D000860:Hypoxia / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D010085:Oxidative Phosphorylation; D010759:Phosphorus Isotopes / Q000737:chemistry / Q000378:metabolism; D011247:Pregnancy; D012756:Sheep
chemical_list: D010759:Phosphorus Isotopes