Effect of prolonged starvation on substrate uptake in the isolated perfused rat heart.

The pattern of substrate uptake by the heart in prolonged starvation, when lipid reserves are approaching depletion, has been examined. The classical Langendorff perfused heart preparation was employed to determine substrate uptakes in male rats fed ad libitum or starved for 7 days. Levels of metabolites in "arterial" and "venous" perfusion media and in heart tissue were determined by fluoroenzymatic assays, with the exception of palmitic acid which was analyzed by gas chromatography. It was found that glucose is the principal fuel of oxidation in perfused hearts of ad libitum-fed rats, whereas palmitate (FFA) is the major fuel of oxidation in perfused hearts of starved rats, followed by lactate, glucose, beta-hydroxybutyrate, pyruvate and alanine. Such changes might be related to some of the alterations in the metabolic pathway (e.g., glycolytic inhibition) in prolonged starvation.