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EXPERIMENTAL STUDIES

Volume overload hypertrophy of the newborn heart slows the maturation of enzymes involved in the regulation of fatty acid metabolism

Paul F. Kantor, MBBCh^*, Murray A. Robertson, MD, PhD, James Y. Coe, MD, MBChB and Gary D. Lopaschuk, PhD^*

^* Cardiovascular Research Group, University of Alberta, Edmonton, Canada
Division of Pediatric Cardiology, University of Alberta, Edmonton, Canada

Manuscript received April 6, 1998; revised manuscript received December 3, 1998, accepted January 21, 1999.

Reprint requests and correspondence: Dr. Paul F. Kantor, 423 Heritage Medical Research Center, University of Alberta, Edmonton, T6G 2S2 Canada
pkantor{at}gpu.srv.ualberta.ca

OBJECTIVES

The purpose of this study was to determine the effect of volume overload hypertrophy in the newborn heart on the cardiac enzymes controlling fatty acid metabolism.

BACKGROUND

Shortly after birth, a rise in 5'-adenosine monophosphate–activated protein kinase (AMPK) activity results in the phosphorylation and inhibition of acetyl coenzyme A (CoA) carboxylase (ACC), and a decline in myocardial malonyl CoA levels with increased fatty acid oxidation rates. Whether the early onset of hypertrophy in the newborn heart alters this maturational increase in fatty acid oxidation is unknown.

METHODS

Newborn piglets underwent endovascular stenting of the ductus arteriosus on day 1 of life with a 4.5-mm diameter stent, resulting in a left to right shunt, and left ventricular (LV) volume loading. Left ventricular and right ventricular samples from fetal, newborn, threeweek control and three-week stented animals were compared.

RESULTS

Stenting resulted in echocardiographic evidence of volume overload and myocardial hypertrophy. In control animals, left ventricular ACC activity declined from 274 ± 30 pmol/mg/min on day 1 to 115 ± 12 after three weeks (p < 0.05), but did not display this maturation drop in hypertrophied hearts, remaining elevated (270 ± 50 pmol/mg/min, p < 0.05). At three weeks, malonyl CoA levels remained 2.8-fold higher in hypertrophied hearts than in control hearts. In control hearts, LV AMPK activity increased 178% between day 1 and three weeks, whereas in hypertrophied hearts AMPK activity at three weeks was only 71% of control values, due to a significant decrease in expression of the catalytic subunit of AMPK.

CONCLUSIONS

Early onset LV volume overload with hypertrophy results in a delay in the normal maturation of fatty acid oxidation in the newborn heart.

Abbreviations and Acronyms   ACC = acetyl coenzyme A carboxylase   AMP = adenosine monophosphate   AMPK = 5' adenosine monophosphate–activated protein kinase   CoA = coenzyme A   LV = left ventricular   PEG = polyethylene glycol   RV = right ventricular

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