In Vivo 31P-MR Spectroscopy of the Liver in the Infant Rabbit to Study the Effect of Hypoxia on the Phosphorus Metabolites and Intracellular pH

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Abstract
In vivo 31P-magnetic resonance spectroscopy (MRS) with a chronically implanted detection coil was used to study the effect of hypoxia on the phosphorus metabolites and intracellular pH in the liver of infant rabbits. A two-turn 10-mm radiofrequency coil was placed between the hepatic lobes in each of four infant New Zealand white rabbits (10-16 days old). Two days later, the rabbits were anesthetized and mechanically ventilated with 1.5% isoflurane in 98.5% O2. Blood gases, heart rate, and mean arterial pressure were monitored. 31P-MR spectra were continuously obtained every 5 minutes during 15 minutes of hyperoxia (PaO2 > 250 torr), 15 minutes normoxia (PaO2 .apprxeq. 100 torr), 60 minutes hypoxia (PaO2 = 24 torr .+-. 4 S.D.), and 15 minutes recovery (hyperoxia). In addition, 31P-MR spectra of perchloric-acid extracts of the liver of an adult and of an infant rabbit, removed under normoxic conditions, were examined. The 31P-MR spectra of liver of the normoxic adult (in vitro) and infant rabbits (in vitro and in vivo) revealed a high level of phosphodiesters, namely glycerol-3-phosphorylethanolamine, glycerol-3-phosphorylcholine, and phosphoenolpyruvate, compared with that reported for adult rat and adult mouse liver. The inorganic phosphate (Pi)-to-adenosine triphosphate (ATP) ratio was about 0.90 during hyperoxia and during normoxia. Within 15 minutes after induction of hypoxia, the level of phosphorus metabolites changed markedly: The ATP decreased 41% .+-. 18 S.D. (P < .01) and the Pi increased 206% .+-. 29 S.D. (P < .01), the Pi/ATP ratio was 5.0. These levels remained quite constant during the next 45 minutes of hypoxia. The intracellular pH declined from 7.33 .+-. 0.05 S.D. during normoxia to 6.97 .+-. 0.16 S.D. 30 minutes after induction of hypoxia. There was partial return of the phosphorus metabolite levels during the subsequent period of recovery. Thus, 31P-MRS can disclose changes in the phosphorus metabolism in the liver of the infant rabbit after a short period of hypoxia.