Oxidative metabolism and citrate synthase activity during the perinatal period were assessed in isolated rabbit heart mitochondria at 27 days’ gestation (27 dpc), 1 day postpartum (1 dpp) and 10 dpp. Oxygen consumption was measured during state 3 and state 4 respiration using the following substrates: glutamate, α-ketoglutarate, pyruvate/malate, succinate/rotenone, acetate, palmitylcarnitine, and palmityl CoA/carnitine. Results obtained from fetal and neonatal animals were compared to values obtained from adult left and right ventricles. Rates of state 3 oxygen consumption per milligram mitochondrial protein using tricarboxylic acid cycle intermediates or palmitylcarnitine were higher in both 1 and 10 dpp animals than in either left or right ventricles. Respiratory activity per milligram mitochondrial protein using these substrates was similar in 27 dpc fetuses and adult left ventricles. The rate of oxidation of palmityl CoA was lower in fetal mitochondria than in adult left ventricle, indicating that the capacity for conversion of long-chain fatty acyl CoA to acylcarnitine necessary for transport of fatty substrates into the mitochondria is decreased in fetal hearts. Increases in myocardial citrate synthase corresponded to increases in mitochondrial mass reported by other investigators.

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