Hypothermic circulatory arrest: 31-phosphorus nuclear magnetic resonsance of isolated perfused neonatal rat brain
Norwood, W.I.; Norwood, C.R.; Ingwall, J.S.; Castaneda, A.R.; Fossel, E.T.
Journal of Thoracic and Cardiovascular Surgery 78(6): 823-830
1979
ISSN/ISBN: 0022-5223 PMID: 41142 Document Number: 141308
Deep hypothermic circulatory arrest facilitates repair of congenital cardiac anomalies in infants. Despite its widespread use, little is known of the fundamental cellular and molecular changes induced. An isolated perfused brain model was developed in part to study high-energy phosphate metabolism with 1-P NMR at 109.3 mHz. Neonatal Sprague-Dawley rats cannulated through the ascending aorta were perfused with modified Krebs-Henseleit buffer. Soft tissues surrounding the calvarium and cervical and thoracic spine were excised and the preparation was lowered into an NMR tube (15 mm outer diameter). Then 200-400 free induction decays (FIDS) were averaged and transformed to produce each spectrum. The 31-P NMR spectra of well-perfused brain show 6 major resonances representing .alpha., .beta. and .gamma. phosphates of ATP, sugar phosphate, Pi and creatine phosphate (CrP). Preparations equilibrated to 37.degree. and 20.degree. C were subjected to 20 min of ischemia with 15-20 min of reperfusion. CrP and ATP levels fell coordinately to 18% .+-. 1% and 34% .+-. 4% of control levels, respectively, by 15 min of normothermic ischemia. This is distinctly different from adult rat heart, where a fall in CrP fell rapidly while ATP remained unchanged. This suggests isolation of creatine kinase from the ATP pool in brain. Following ischemia at 37.degree. C, ATP and CrP recovered substantially but failed to return to control levels (51% .+-. 9% and 44% .+-. 12%, respectively). Following ischemia at 20.degree. C, ATP and CrP returned to control levels by 20 min. Intracellular pH determinations by chemical shift of Pi revealed a decrease from 7.2-6.7 during ischemia at 37.degree. C, whereas pH at 20.degree. C remained unchanged above 7.2. NMR proved a valuable tool for studying high-energy phosphate metabolism in brain. Permanent changes in ATP and CrP pools induced by 20 min of normothermic ischemia are evidently attenuated whereas intracellular pH changes are abated by hypothermia.