Heart microperoxisomal beta-oxidation activity, measured as cyanide-insensitive palmitoyl-CoA-dependent NAD+-reduction, was detected in a microperoxisome-enriched fraction from rat myocardium. The effect on this microperoxisomal beta-oxidation of the fatty acid composition of the dietary oils was investigated. 2. Feeding 15% (w/w) high erucic acid rapeseed oil or partially hydrogenated marine oil for 3 weeks increased the microperoxisomal beta-oxidation in the heart 4-5-fold, compared to a soybean oil diet. Increasing amounts (5-30%, w/w) of partially hydrogenated marine oil in the diet led to a 3-fold increase in the microperoxisomal beta-oxidation capacity at 20% or more of this oil in the diet. 3. The activity of the microperoxisomal marker enzyme catalase followed closely the cyanide-insensitive palmitoyl-CoA-dependent NAD+-reduction, except when feeding more than 20% (w/w) partially hydrogenated marine oil where a significant decrease in the catalase activity was observed. 4. In rapeseed oil-fed animals the extent of increase of microperoxisomal beta-oxidation was directly correlated to the amount of erucic acid (22:1, n-9 cis) in the diet. 5. Feeding partially hydrogenated rapeseed oil or partially hydrogenated soybean oil resulted in activities of microperoxisomal beta-oxidation significantly lower than in the corresponding unhydrogenated oils. No significant difference could be detected between diets containing hydrogenated or unhydrogenated marine oil. 6. Addition of 5% soybean oil to the essential fatty acid-deficient, partially hydrogenated marine oil diet did not change the effect on the microperoxisomal beta-oxidation activity. 7. Clofibrate feeding increased the heart microperoxisomal beta-oxidation capacity 2.5-fold, as compared to a standard pelleted diet. 8. These findings are discussed in relation to the transient nature of the cardiac lipidosis observed with animals fed on diets rich in C22:1 fatty acids. It is concluded that the heart plays an important part in the adaptation process.
