Effects of Hypoxic Hypoxia on Cerebral Phosphate Metabolites and pH in the Anesthetized Infant Rabbit

Abstract

Summary:The effects of hypoxic hypoxia on high-en ergy phosphate metabolites and intracellular pH (pH) in the brain of the anesthetized infant rabbit were studied in vivo using 31p nuclear magnetic resonance spectros copy. Five 10c to 16-day-old rabbits were anesthetized with 1.5% halothane. Ventilation was controlled to main tain normocarbia . Inspired 07 fraction was adjusted to produce three states of arterial oxygenation: hyperoxia (Pao2 > 250 mm Hg), normoxia (Pao2 �100 mm Hg), and hypoxia (Pao2 25-30 mm Hg). During hypoxia, blood pressure was kept within 20% of control values with a venous infusion of epinephrine. During hyperoxia, the phosphocreatine-to-ATP ratio was 0.86, a value that is 2-2.5 times less than that reported for adults. During norNeonates survive longer periods of anoxia than adults of the same species. Similarly, hypoxic ne onates sustain less central nervous system injury than adults (Dawes, 1968). This cannot be explained by a more efficient oxygen delivery system or ce rebrovascular response (Koehler et aI., 1984). It is possible that neonates have a better neurologic out come after oxygen deprivation because their cere bral energy stores are maintained more effectively than in adults. Duffy et al. (1975) used freeze extraction to mea sure cerebral phosphocreatine (PCr) and ATP in newborn and older rats and found that PCr levels were higher in the latter. They also found that global 512 moxia, ATP decreased by 20% and Pi increased by 90% from hyperoxia values. During 60 min of hypoxia, the concentrations of high-energy phosphate metabolites did not change, but intracellular and arterial blood pH (pH) decreased significantly. When hyperoxia was reestab lished, pHi returned to normal and pHa remained low. These results suggest that during periods of hypoxemia, the normotensive infant rabbit maintains intracellular concentrations of cerebral high-energy phosphates better than has been reported for adult animals. Key Words: Brain metabolism-Halothane anesthesia-Hypoxic hypoxia-Infant rabbit-In ViVO_31p nuclear magnetic resonance.ischemia depleted ATP and PCr levels more rapidly in the brain of older animals. Norwood et al. (1979) used 31 p nuclear magnetic resonance (NMR) spec troscopy to study the perfused neonatal rat brain and found the PCr signal intensity to be approxi mately the same as the ATP signal intensity. The brain PCr/ATP ratio seen by 31 p NMR in normal human infants was also � 1.0 (Cady et aI., 1983). Norwood et al. (1983) calculated the half-life of PCr in the ischemic brain to be 7.5 min in the neonate and 3.3 min in the adult, confirming the earlier work of Duffy et al. (1975).We have studied the effects of hypoxic hypoxia on cerebral intracellular phosphate metabolites and on intracellular pH (pH) in anesthetized normoten sive infant rabbits. This study, performed in vivo using 31 p NMR, shows that arterial oxygen tensions that provoke changes in intracellular phosphate me tabolite concentrations in the brain of the adult an imal do not produce these changes in the brai...

31P magnetic resonance spectroscopy of traumatic spinal cord injury

“…These ratios were much greater than those previously reported for rabbit CNS tissue (13), and in fact, were similar to values reported for muscle (14). Furthermore, following injury in these pilot studies, no significant changes in pH, PCr/Pi, or PCr/ATP were observed (results not shown), despite physiological and neurological changes that were consistent with severe injury (Vink and Faden, unpublished results).…”

Alterations in Cerebral Blood Flow and Phosphorylated Metabolites in Piglets during and after Partial Ischemia

“…As noted by others (25), a pool of PCr persists when ATP decreased during ischemia, suggesting compartmentation of PCr in the brain as speculated for muscle (33). Alternative explanations include differential rates of fall of PCr and ATP during intracellular acidosis (25) (35,36). Considerable variation existed among piglets for the control PCr/Pi ratios but within a litter values tend to cluster (Fig.…”

31P Nuclear Magnetic Resonance Study of the Effect of Hypoxemia on Neonatal Status Epilepticus

“…More recent in vivo 31 p NMR studies by Gonzalez-M endez et at. (34) and Prichard et at. (7) show th at rabb its maintain normal levels of ATP during hypoxia and met aboli c acidosis.…”