Effect of prolonged exercise of moderate intensity on incorporation of the blood-borne 14C-palmitic acid into different lipid fractions in the rat heart

Exercise increases consumption of the blood-borne free fatty acids by the heart. Upon entering the cardiomyocytes, the acids are oxidised and/or esterified into complex lipids. Only a tiny fraction remains "free". The aim of the present study was to examine effect of prolonged exercise on the incorporation of the blood-borne C-14-palmitic acid into different lipid fractions of the rat heart. The experiments were carried out on male Wistar rats with a body weight of 250-280 grams. The rats were divided into two groups: I-fed ad libitum, and II-fasted 24 h before the final experiment. Each group was divided into two subgroups: (a) resting, and (b) run 3 h on a treadmill set at +10(o) and moving with a speed of 1200 m/h. The rats were anaesthetised with pentobarbital sodium and each rat received 14 C-palmitic acid at a dose of 20 muCi/100g, intravenously. 20 min after administration of the label, samples of blood from the abdominal aorta and the left ventricle were taken. Lipids were extracted from the sample of the heart with chloroform/m ethanol (2:1) and separated into the following fractions using thin layer chromatography: phospholipids, mono-,di-, and triacylglycerols, free fatty acid, cholesterol and cholesterol esters. The radioactivity of each fraction was counted. It was found that exercise reduced the total radioactivity of lipids in the fed group. This was accounted for by a reduction in the radioactivity of each lipid fraction with the exception of the cholesterol fraction. Fasting reduced the total radioactivity of lipids at rest. This was the consequence of a reduction in the radioactivity of the fraction of di-, and triacylglycerols. Exercise did not affect the total radioactivity of lipids in the fasted group. However, it reduced the radioactivity of the phospholipid fraction and increased the radioactivity of the triacylglycerol fraction. The specific activity of the plasma free fatty acids was reduced in both groups after exercise and in the fasted group at rest in comparison to the resting value in the fed group. Taking the latter result into account. one can conclude that exercise in the fed group and fasting increase incorporation of the blood-borne fatty acids into the heart lipids to a moderate extent. Exercise also changes the distribution of the C-14 label among different lipid fractions in both the fed and Fasted group.