Developmental changes in atp utilization during graded hypoxia and reoxygenation in the heart in vivo. Portman, Michael A., Thomas A. Standaert, and Xue-Han Ning. Division of Cardiology, Department of Pediatrics, University of Washington and Childrens Hospital and Medical Center of Seattle, Seattle WA
APStracts 2:0272H, 1995.
Myocardial ATP utilization and resynthesis during hypoxia and reoxygenation were studied in vivo as a function of maturation. Graded hypoxia was performed in newborn (NB) ( age 4-10d, n=6)) and mature sheep (MAT) (30-60d, n=6). Time resolved 31P NMR was used to monitor myocardial phosphates throughout hypoxia and reoxygenation concomitant with MVO2 measurement. Oxygen delivery and MVO2 were constant in both groups through hypoxia, with substantial and similar increases in both during reoxygenation. Hypoxic myocardial lactate release was similar in NB and MAT. Phosphocreatine (PCr), but not ATP decreased in NB only during milder hypoxia. Rapid PCr and slower ATP depletion occurred with severe hypoxia, consistent with ATP utilization/synthesis imbalance. Depletion rates were higher in MAT. Creatine rephosphorylation rates, measures of mitochondrial function reported as %predicted, were similar : 34% +/- 12 NB and 26 +/- 9 in MAT. Conclusions: 1) phosphorylation potential decreases in NB but not MAT in response to a decreasing oxygen gradients; 2) ATP utilization during hypoxia increases more in MAT lambs ; 3) anaerobic ATP production is not greater in NB; 4) despite the greater energy imbalance imposed on MAT during hypoxia, mitochondrial function is similar to NB during reoxygenation. 

Received 23 February 1995; accepted in final form 15 June 1995.
APS Manuscript Number H170-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 11 July 1995.