G.A. Gresham

Modification of enzyme activities in experimental atherosclerosis in the rabbit

Abstract In rabbits fed an atherogenic semi-synthetic diet, the following were found: in the aortic wall, decreased cholesterol esterase and increased lipase and phospholipase A activities, no changes in malate and lactate dehydrogenase activities, enhanced incorporation of free fatty acid into cholesterol esters, and increased accumulation of mainly esterified and also free cholesterol; increase in plasma cholesterol and serum phospholipase A activity but no change in liver phospholipase A and serum and liver lipase activities. Compared with control animals, those fed the same diet and injected with Lipostabil (a drug containing polyunsaturated lecithin) showed no alterations in the aortic enzyme activities and serum phospholipase A and in the incorporation of free fatty acid into aortic cholesterol esters; serum and liver lipase activities were increased. Compared with atherogenic diet-fed animals injected with saline, the severity of atherosclerosis and the incorporation of free fatty acids into the aortic wall were reduced; there was no change in the elevated plasma cholesterol levels. The mechanism of cholesterol ester accumulation in the arterial wall is discussed in the light of these observations.

Changes in phospholipase a, lipase and cholesterol esterase activity in the aorta in experimental atherosclerosis in the rabbit and rat

Summary Esterase activity has been examined in the aorta of rats given hyperchol-esterolaemic, thrombogenic or atherogenic diets, and rabbits given an atherogenic, semi-synthetic diet low in cholesterol. In normal rat aorta, the specific activity values are in the numerical order of phospholipase A > lipase > cholesterol esterase. In the rabbit the activities were in the same order but of much lower magnitude. In the rat, feeding an atherogenic diet containing 40 % peanut oil, 5 % cholesterol and 2 % cholic acid produced an increased phospholipase A and lipase, and a decreased cholesterol esterase activity compared with normal animals. Replacement of peanut oil with butter produced no change in phospholipase A and cholesterol esterase and only a small increase in lipase. Thiouracil depressed the higher lipase and abolished the increased phospholipase A activity of the peanut oil group, and decreased cholesterol esterase in both the butter and peanut oil groups. In rabbits given the semi-synthetic low cholesterol diet for 10 and 32 weeks, a decrease in phospholipase A and cholesterol esterase activity was seen compared with normal animals. An increased lipase activity was seen at 10 weeks but not at 32 weeks. It is concluded that the high lipase and low cholesterol esterase activity in the peanut oil fed rat, and the low cholesterol esterase activity in the semi-synthetic diet fed rabbit may be contributing factors in the dietary production of atherosclerosis in these two species.

The prevention of rabbit atherosclerosis by soya bean meal

Summary Groups of rabbits were given an atherogenic diet containing 20 % beef tallow for 16 weeks and the aortae examined macroscopically after staining with Sudan. Variations of this diet were made by replacing various constituents by other “natural products”. Substitution of beef tallow by corn oil prevented the hypercholesterol-aemia but not the arterial lesions, although they were less severe. Replacement of the vitamin mixture by yeast and cabbage, corn starch by corn meal, mineral mix by bone meal or bone ash and casein by purified soya bean proteins did not effect the aortic atherosclerosis or hypercholesterolaemia. However, replacement of casein by whole soya flour and hexane-extracted soya bean meal was more effective in preventing the disease. It is suggested that the rabbit natural diet contains a nutrient which prevents atherosclerosis and which is also present in extracted soya bean meal. Preliminary attempts to isolate this factor show that it is not purified soya protein, phospholipid or triglyceride. It is unlikely the disease is caused by a toxic factor since no one constituent was essential and also rabbits given a mixture of natural diets and atherogenic diet did not have the disease.

Lipid changes in the plasma lipoproteins of baboons given an atherogenic diet

Abstract Plasma from normal human subjects and those with type II hyperlipoproteinaemia were separated into α- and β-lipoproteins by electrochromatography; the lipoprotein fractions were analysed for lipid and fatty acid composition. These data were then compared with those obtained previously in baboons and chimpanzees fed control and atherogenic diets. In type II hyperlipoproteinaemia the increases in the free and esterified cholesterol and cholesterol/phospholipid (C/PL) ratio were chiefly in the β-lipoproteins, but changes in the same direction also occurred in the α-lipoproteins. Increases in the concentration of phosphatidyl choline (PC), lysophosphatidyl choline (OH-PC), and sphingomyelin (S) were confined to the β fraction only. An increase in the cholesterol/phosphatidylcholine ratio occurred in both lipoproteins. Differences in the fatty acid composition of both lipoproteins were noted. Cholesterol oleate was elevated more than cholesterol linoleate so that the ratio 18:118:2 was increased. These changes were similar in baboons and chimpanzees, except that in the chimpanzee the increase in cholesterol was confined solely to the β-lipoprotein and the C/PL ratio was increased more in the β than α-lipoprotein. The normal plasma C/PL ratio and the elevated arachidonic acid seen in earlier studies in the baboon were attributed to the egg yolk used in the diet, because when this ingredient was omitted the changes resembled those in man. The increase in sphingomyelin in β-lipoproteins was much greater in man and chimpanzee than in the baboon. It is concluded that both the chimpanzee and baboon fed atherogenic diets provide experimental models for the type II hyperlipoproteinaemia that occurs in man, and that there is a distinct similarity in the change of the lipid composition of the lipoproteins among the three species.

Aortic rupture in the Turkey

Summary The histo-pathological appearances of dissecting aneurysm in broad breasted bronze turkeys are described. An intimai plaque found at the site of rupture contained lipid in the region of the internal elastic lamina and it is suggested that this may be the primary lesion. The possible relationship of this lesion to diet is discussed.

Lipid changes in the plasma lipoproteins of baboons given an atherogenic diet part 2. Changes in the phospholipid classes of total plasma and of α- and β-lipoproteins☆

Abstract The phospholipid classes of total plasma and of α- and β-lipoproteins, in baboons given control and atherogenic diets, have been studied using the techniques of electrochromatography (ECG), thin-layer chromatography (TLC) and gas-liquid chromatography (GLC). In animals given an atherogenic diet, a 70 % increase in plasma phospholipids (mg/ 100 ml) could be attributed to rises in all phospholipids in the β-lipoproteins but chiefly phosphatidyl choline (PC). Phospholipids in the a-lipoproteins were not appreciably affected. Arachidonic acid (mg/100 ml) was increased 2-fold in plasma phosphatidyl ethanolamine (PE) and 3-fold in plasma phosphatidyl choline (PC). However, the increase of arachidonic acid was most pronounced in the β-lipoproteins. The percentage value of polyunsaturated fatty acids and of unsaturated fatty acids remained constant at 35 and at 50% in PE and PC, respectively. It is concluded that the rise in PC in the β-lipoproteins is in response to the increased cholesterol transported in this fraction. There was no evidence to support the hypothesis that a raised cholesterol/phospholipid ratio is an index of athero geneity. The unexpected large increase in arachidonic acid which replaced linoleic acid in PE and PC was probably derived from its relatively large concentration in the atherogenic diet. For animals on the same diet the percentage fatty acid composition of α-PC and β-PC were similar, and likewise for α-PE and β-PE. This suggests that the phospholipids in each of the lipoproteins arise from the same body pool.

Comparative histopathology of the atherosclerotic lesion

Summary The early atherosclerotic lesion of man is described and compared with that seen in naturally occurring disease in animals and in the experimental animal. A prototype lesion composed of collagen, elastin, mucopolysaccharide and some lipid is common to all and suggests that the early atherosclerotic lesion in man and animals begins as a repair to injury the cause of which is unknown.

The histogenesis of the atherosclerotic "fatty streak".

Summary A histochemical study of human “fatty streaks” has indicated the probable mechanism involved in their development. Clefts in the lesion consisted of spindle-shaped spaces containing a central nucleus encrusted with lipid. Around the clefts was a condensation of acid sulphated mucopolysaccharide, protein and reticulin. It is suggested that these clefts are foci of collagen production.

Aetiology of “yellow fat” disease (pansteatitis) in the wild rabbit

Abstract “Yellow fat” disease in the wild rabbit has been studied, and a similar condition has been induced in laboratory rabbits. The cause is a high level of dietary unsaturated fat and a low level of vitamin E. High levels of vitamin E, fed in a diet containing unsaturated fats, prevent “yellow fat” disease, but apparently cause or permit deposition of lipid in arterial walls.

The effect of atromid on arterial disease induced by semi-synthetic diet in the rabbit

Summary Hypercholesterolaemia and atherosclerosis can be produced in rabbits by feeding a semi-synthetic diet containing 20 % beef fat without added cholesterol. Atromid fed at a level of 0.3 % w/w in the diet will significantly reduce plasma cholesterol levels in such animals, but has no effect on the severity of the atherosclerotic lesions.