In vitro fatty acid oxidation rates in rat heart and liver

Oxidation of oleic and elaidic acids in rat and human heart homogenates

Parallel incubations with uniformly 14C-labeled oleic and elaidic acids were conducted to compare oxidation rates in tissue homogenates prepared from rat and human hearts. Radioactivity in 14CO2 and 14C-labeled chain-shortened acid-soluble products was used to measure the extent of oxidation. Oxidation rates (pmol/min per mg heart protein) determined on 14C-labeled acid-soluble products suggest that oleic acid was oxidized 35-40% faster than elaidic acid by both male and female rat heart homogenates, whereas human heart homogenates oxidized these fatty acids at equal rates. Rates for female heart homogenates were somewhat higher than those for males in rats and humans. Rates of formation of 14CO2 were the same for each acid in rat and human heart tissue. Comparative rates of formation of oxidation products expressed as oleic/elaidic ratios from parallel incubations confirm that preferential oxidation of oleic acid occurred with rat heart homogenates, but not with the human heart homogenates. These data suggest that the presence of the trans double bond in elaidic acid does not impair its utilization for energy by human heart muscle.

Differences in the fatty acid profile and beta-oxidation by heart homogenates of rats fed cis and trans octadecenoic acids

Female Wistar rats were fed a fat-free diet containing either 5% partially hydrogenated corn oil (52.2% elaidate) or 5% oleic acid (67% oleate) with 8.6% linoleate providing 1% of calories 2 weeks before mating and were maintained on this diet throughout pregnancy and lactation. Fatty acid analysis of the developing organs as well as beta-oxidation by heart homogenates with [1-14C]palmitate, [1-14C]elaidate and [1-14C]oleate of the developing male and female progeny were determined and compared with age-matched controls on a stock diet. Results show that irrespective of the cis and trans 18:1 in the diet, the maternal plasma at term contained mostly cis 18:1, with 5% trans for the rats on the trans diet. The placenta and fetal liver contained 40 and 60% less trans, respectively, than did the maternal plasma. trans 18:1 was not detected in fetal brain or heart. Regardless of diet or sex, the order of preference for the heart was palmitate greater than elaidate greater than oleate. There was an increase in the rate of beta-oxidation of all the substrates, especially in the females on the trans diet, suggesting a stimulation of one or more of the enzymes involved. Above all, the myocardium showed a unique capacity to retain n-6 and n-3 fatty acids when the levels of these decreased in the serum.

Fatty acid and cholesterol synthesis from specifically labeled leucine by isolated rat hepatocytes

Hepatocytes isolated from female rats meal-fed a high-glucose diet were incubated in Krebs-Henseleit bicarbonate medium containing 16.5 mM glucose, 3H2O, and 14C-labeled amino acids (-)-Hydroxycitrate depressed the incorporation of 3H2O and [14C] alanine into fatty acids and cholesterol. Incorporation of [U-14C]leucine into lipids was not affected but incorporation of 3H2O into lipids was decreased significantly by (-)-hydroxycitrate. (-)-Hydroxycitrate depressed the incorporation of radioactivity from [2-14C]leucine into fatty acids and cholesterol by 61 and 38%, respectively, and stimulated the incorporation of radioactivity from [4,5-3H]leucine 35 and 28%. As [2-14C]leucine labels the acetyl-CoA pool and [4,5-3H]leucine labels the acetoacetate pool, it was concluded that mitochondrial 3-hydroxy-3-methylglutaryl-CoA is not incorporated intact into cholesterol, and that acetoacetate can be activated effectively in the liver cytosol for support of cholesterol and fatty acid synthesis.