Comparison of lipid status in the hearts of piglets and rats on short term feeding of marine oils and rapeseed oils

Lipids and cardiac arrhythmia

In any discussion of lipids and heart disease it is beneficial from the outset to recognise that at least three different pathological processes may be involved. The first of these is atherosclerosis which involves the deposition of "fat" in the coronary vessels, another is thrombogenesis which describes the formation of blood clots in the coronary vessels, and the third is arrhythmia which refers to disorders in the beating of the heart which may become sufficiently serious to cause sudden cardiac death (SCD). Also it is this disturbance in the rhythmic beating of the heart which is responsible for much of the mortality from 'heart attacks' which occur 'outside-of-hospital' in societies like U.S.A., U.K. and Australia. It is this latter condition of cardiac arrhythmia which is the major concern of this review. Because it is often difficult to differentiate the role of lipids in 'heart disease' in man, it has frequently been assumed that all dietary fatty acids have similar effects on the different processes involved, and many unwarranted generalisations have been made which have led to conflicts of opinion amongst physicians and confusion in the lay public. From the animal studies discussed in this review, it is apparent that dietary fatty acids have an important role to play in determining the vulnerability of the myocardium to develop serious ventricular fibrillation (VF) and potentially lethal cardiac arrhythmia. In general, diets rich in saturated fatty acids promote a state of myocardial vulnerability, whilst diets rich in PUFA significantly diminish the probability of developing lethal disorders in cardiac rhythm when the heart is placed under pharmacological (or emotional) stress, or deprived of sufficient blood flow and supply of oxygen. Very recent experiments with the monounsaturated fatty acid (MUFA) oleic acid clearly demonstrate that, at least in rats subjected to ligation of their coronary artery, this acid is not 'neutral' as has been suggested by some for its role in atherosclerosis, but in fact is indistinguishable from saturated fatty acids in its effect in promoting arrhythmia during either regional ischaemia or reperfusion arrhythmia in this animal model of SCD.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of dietary saturated fat on erucic acid induced myocardial lipidosis in rats

Male Sprague-Dawley rats were fed for one week diets containing 20% by weight fat/oil mixtures with different levels of erucic acid (22:1n-9) (approximately 2.5 or 9%) and total saturated fatty acids (approximately 8 or 35%). Corn oil and high erucic acid rapeseed (HEAR) oil were fed as controls. The same hearts were evaluated histologically using oil red O staining and chemically for cardiac triacylglycerol (TAG) and 22:1n-9 content in cardiac TAG to compare the three methods for assessing lipid accumulation in rat hearts. Rats fed corn oil showed trace myocardial lipidosis by staining, and a cardiac TAG content of 3.6 mg/g wet weight in the absence of dietary 22:1n-9. An increase in dietary 22:1n-9 resulted in significantly increased myocardial lipidosis as assessed histologically and by an accumulation of 22:1n-9 in heart lipids; there was no increase in cardiac TAG except when HEAR oil was fed. An increase in saturated fatty acids showed no changes in myocardial lipid content assessed histologically, the content of cardiac TAG or the 22:1n-9 content of TAG at either 2.5 or 9% dietary 22:1n-9. The histological staining method was more significantly correlated to 22:1n-9 in cardiac TAG (r = 0.49; P less than 0.001) than to total cardiac TAG (r = 0.40; P less than 0.05). The 22:1n-9 content was highest in cardiac TAG and free fatty acids. Among the cardiac phospholipids, the highest incorporation was observed into phosphatidylserine, followed by sphingomyelin. With the addition of saturated fat, the fatty acid composition showed decreased accumulation of 22:1n-9 and increased levels of arachidonic and docosahexaenoic acids in most cardiac phospholipids, despite decreased dietary concentrations of their precursor fatty acids, linoleic and linolenic acids.

Myocardial changes in newborn piglets fed sow milk or milk replacer diets containing different levels of erucic acid

This study was undertaken to determine whether the neonate was more susceptible to the effects of dietary erucic acid (22:1n-9) than the adult. Newborn piglets were used to assess the safety of different levels of 22:1n-9 on lipid and histological changes in the heart. Newborn piglets showed no myocardial lipidosis as assessed by oil red 0 staining, but lipidosis appeared with consumption of sow milk and disappeared by seven days of age. Milk replacer diets containing soybean oil, or rapeseed oil mixtures with up to 5% 22:1n-9 in the oil, or 1.25% in the diet, gave trace myocardial lipidosis. Rapeseed oil mixtures with 7 to 42.9% 22:1n-9 showed definite myocardial lipidosis in newborn piglets, which correlated to dietary 22:1n-9, showing a maximum after one week on diet. The severity of the lipidosis was greater than observed previously with weaned pigs. There were no significant differences among diets in cardiac lipid classes except for triacylglycerol (TAG), which increased in piglets fed a rapeseed oil with 42.9% 22:1n-9. TAG showed the highest incorporation of 22:1n-9, the concentration of 22:1n-9 in TAG was similar to that present in the dietary oil. Among the cardiac phospholipids, sphingomyelin and phosphatidylserine had the highest, and diphosphatidylglycerol (DPG) the lowest level of 22:1n-9. The low content of 22:1n-9 in DPG of newborn piglets is not observed in weaned pigs and rats fed high erucic acid rapeseed oil. The relative concentration of saturated fatty acids was lowered in all cardiac phospholipids of piglets fed rapeseed oils, possibly due to the low content of saturated fatty acids in rapeseed oils. The results suggest that piglets fed up to 750 mg 22:1n-9/kg body weight/day showed no adverse nutritional or cardiac effects.

Effect of tissue fat and water content on nuclear magnetic resonance relaxation times of cardiac and skeletal muscle

Understanding tissue determinants that affect the nuclear magnetic resonance (NMR) properties of myocardium would improve noninvasive characterization of myocardial tissue. To determine if NMR relaxation times would reflect changes in tissue fat content, two experimental models were investigated. First, an idealized model using mixtures of beef skeletal muscle and beef fat was studied to investigate the effects of a wide range of tissue fat content. Second, myocardium with varying fat content from hogs raised to have varying degrees of ponderosity was analyzed. Tissue fat and water contents and spin-lattice (T1) and spin-spin (T2) relaxation times at 20 MHz were measured. The skeletal muscle/fat mixtures ranged in fat content from 35% to 95% with water content variations from 50% to 75%. Water content decreased as fat content increased. A significant inverse linear relationship was found between T1 and sample fat content (r = -0.997). Spin-spin relaxation times showed a significant positive curvilinear relationship with fat content (r2 = 0.96). In the animal experiments, 18 hogs were studied with samples obtained from both right and left ventricular (LV) free walls, with care taken to avoid epicardial fat. Myocardial fat content ranged from 3% to 25%. A significant correlation was found between LV fat content and corrected LV mass (r = 0.62), which suggested that the increase in LV mass could be explained, at least in part, by changes in myocardial fat content. Similar to the muscle/fat mixture model, a significant positive curvilinear relationship was found between myocardial T2 and tissue fat content (r2 = 0.67) for all the myocardial samples.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered acyl chain compositions of alkylacyl, alkenylacyl, and diacyl subclasses of choline and ethanolamine glycerophospholipids in rat heart by dietary fish oil

The effects of dietary fish oil containing n - 3 polyunsaturated fatty acids on the fatty acid compositions of the alkylacyl and alkenylacyl species of choline glycerophospholipids (CGP) and ethanolamine glycerophospholipids (EGP) were studied in rat heart and compared with the corresponding diacylglycerophospholipids. After a 7 week feeding period, all phospholipid classes from the fish oil group exhibited much higher levels of the n - 3 polyunsaturated fatty acids including eicosapentaenoic acid (20:5(n - 30)), docosapentaenoic acid (22:5(n - 3)) and docosahexaenoic acid (22:6(n - 3)), as well as lower levels of the n - 6 series (18:2, 20:4, 22:4 and 22:5), relative to animals given sunflower seed oil-enriched in 18:2(n - 6). However, the docosahexaenoic acid rather than eicosapentaenoic acid provided a much greater contribution to the n - 3 accumulation (fish oil group) in the ether-containing CGP, as indicated by the 20:5(n - 3)/22:6(n - 3) molar ratios of 0.32, 0.26 and 0.56 in the alkylacyl, alkenylacyl and diacyl classes, respectively. In addition to accumulating very high levels of docosahexaenoic acid (e.g., 47.2 mol% of fatty acids in alkenylacylglycerophosphoethanolamine of fish oil group), both ether-linked classes of EGP exhibited significantly higher levels of docosapentaenoic acid than the diacylglycerophosphoethanolamine (GPE) and all classes of CGP. These findings may bear relevance to possible beneficial effects of dietary fish oil on pathophysiological states (including myocardial ischemia) in cardiac tissue and their mediation via platelet-activating factor, 1-alkyl-2-acetylglycerophosphocholine (PAF) and arachidonic acid (20:4(n - 6))-derived eicosanoids.

Dietary fatty acids and myocardial function

It is widely recognized that dietary polyunsaturated fatty acids (PUFA's) and cholesterol can profoundly influence the development of atherosclerotic plaques in coronary vessels, which may lead to myocardial infarction. The possibility that dietary fatty acids may also directly influence cardiac function has received less attention. We therefore reviewed the evidence of the effects of dietary fatty acids, in particular n-3 and n-6 PUFA's, on myocardial phospholipid fatty acid composition and cardiovascular performance. Heart organelles appear to incorporate uncommon fatty acids like 22:1 and trans- 18:1. Diets enriched with 22:1 induce myocardial lipidosis. N-9, n-6 and n-3 families compete among membrane C20 and C22 acids. Several studies have dealt with the relation between diet-induced changes of cardiac membrane (sarcolemma, sarcoplasmic reticulum and mitochondria) phospholipids and membrane function. In view of the variety of diets used and of the membrane functions studied, the results do not permit equivocal interpretation. Several investigators have reported an altered stress response of the heart due to a change of PUFA's in the diet. In rats fed with a low 18:2n-6/18:3n-3 ratio combined with relatively low amounts of saturated fatty acids, a high incidence of myocardial lesions has been observed. Pigs are less sensitive but more susceptible to the development of vitamin E deficiency, when the dietary PUFA content is high. Increased contractility and coronary flow rate have been reported for Langendorff-perfused hearts of rats fed 18:2n-6-rich diets. The effects on coronary flow rate are possibly related to alterations in eicosanoid synthesis, which may also contribute to the reduction by n-6 or n-3 PUFA's in infarct size, magnitude of recovery of function and suppression of reperfusion arrhythmias following release of a coronary artery ligation. On the other hand, increased peroxidation of membrane lipids, due to their high content of n-3 PUFA, may be deleterious.

The composition of cardiac phospholipids in rats fed different lipid supplements

Changes in dietary lipid intake are known to alter the fatty acid composition of cardiac muscle of various animals. Because changes in cardiac muscle membrane structure and function may be involved in the pathogenesis of arrhythmia and ischemia, we have examined the effects of dietary lipid supplements on the phospholipid distribution and fatty acid composition of rat atria and ventricle following 20 weeks feeding of diets supplemented with either 12% sunflower-seed oil or sheep fat. Neither lipid supplement produced significant changes in the proportions of cholesterol, total phospholipids or phosphatidylcholine, phosphatidylethanolamine or diphosphatidylglycerol,--the phospholipid classes that together account for more than 90% of the total phospholipids of rat cardiac muscle. Significant changes were found in the profiles of the unsaturated fatty acids of all 3 phospholipid components of both atria and ventricle. Although similar, the changes between these tissues were not identical. However, in general, feeding a linoleic acid-rich sunflower seed oil supplement resulted in an increase in the omega-6 family of fatty acids, whereas feeding the relatively linoleic acid-poor sheep fat supplement decreased the level of omega-6 fatty acids but increased the levels of the omega-3 family, resulting in major shifts in the proportions of these families of acids. In particular, the ratio of arachidonic acid: docosahexaenoic acid (20:4,omega-6/22:6,omega-3), which is higher in all phospholipids of atria than ventricle, is increased by feeding linoleic acid, primarily by increasing the level of arachidonic acid in the muscle membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

Morphological changes and fatty acid composition in hearts from pigs fed rapeseed oil, fish oil, partially hydrogenated fish oil, partially hydrogenated soybean oil and lard

Female pigs, fed diets in which 42% of the caloric intake came from either rapeseed oil, fish oil, partially hydrogenated fish oil, partially hydrogenated soybean oil or lard, were killed after one week, five weeks, six months and one year. Type of fat or length of feeding did not affect the cardiac content of total fat which was normal in all animals. The fatty acid pattern of tissue triglycerides only partly reflected the fatty acid pattern of diets. The relative amounts of C22:1 and C20:1 were greatest after six months and levelled off during the following six months. The content of C22:1 in cardiac triglycerides never exceeded one fifth of the dietary concentration. Microscopic lipidosis was found in some pigs after one week, five weeks and six months. Minor heart lesions consisting of focal necrosis of muscle cells were found after one week and more frequently after six months and one year. No relationship between incidence and severity of the heart lesions and any particular type of fat in the diet could be found.