대동맥 중막(大動脈 中膜)의 화학적손상이 cholesterol 식이성 가토동맥경화증(食餌性 家兎動脈硬化症)에 미치는 영향에 관한 실험적 연구
The nature and etiology of athero-arteriosclerosis in human beings are diverse and complicated. In spite of innumerable investigation to clarify its cause and pathogenesis, no unifying conception was been reached at the present.
Reliable method to induce atherosclerosis in animals resembling that of human beings, so far, is achieved only by excessive cholesterol feeding (Jobling and Meeker 1936), However, many investigators raised objections against transposing the data obtained from animal experiments to human disease based on following reasons.
Grossly, experimental cholesterol-fed atherosclerosis in animals show lesions predominantly at the ascending and thoracic portions of the aorta; main branches of the arteries arising from the aorta; and frequently in the pulmonary arteries with association of heavy lipids deposition in parenchymatous organs and reticular tissue, such as the adrenals and the liver: and mostly cerebral and retinal vessels are net involved. Whereas atherosclerosis in human involves predominantly abdominal portion of the aorta: cerebral and retinal arteries are frequent sites of
involvement; pulmonary arteries are usually spared: and it is never associated with lipid deposition in the other organs (Duff and McMillan 1951).
Histologically, truman atherosclerosis is complex combination of lipid deposition, degenerative changes, calcification, or necrosis involving usually more than the intima of the aortic wall.
However, experimental atherosclerosis is mostly simple lipids deposition in the intima, and does not develop into chronic progressive form (Hass et al. 1960, Hess and Staubli 1963).
The importance of lipids and cholesterol in the atherogenesis and among the constituents of atherosclerotic lesions are well known. However, the mechanisms how lipids have reached there and particularly about the selective localization at certain areas have not been elucidated (Duff and McMillan 1951). Some investigators stressed the importance of the role of the internal elastic membrane, while others thought there must be some start of visible and invisible damage in the media of the affected areas to localize the disease process. Therefore, it was thought to be worthy to investigate role of medial injuries of the aorta to cholesterol-fed atherosclerosis, with special attempt to produce atherosclerotic lesions closer to that of human.
Materials and Methods
Seventy-two albino rabbits, around 2 kg in body weight, are divided into 12 groups, comprising 6 animals in each group. Medial injuries were produced by the administration of epinephrine, thyroxine and vitamin D in various combinations, and
cholesterol were given alone and in combination with epinephrine, thyroxine, and vitamin D in different combinations.
Epinephrine, Premo Pharma. Co. product, were given for 10 days in doses of 0.05 mg per kg of animal weight, alone or prior to cholesterol feeding. Thyroxine, North American Lab. product, were given for 5 days in doses of 1 mg per kg of animal weight, alone or in combination with other agents. Vitamin D (calciferol) were
given once every three days for 60 days in doses of 20,000 u. per animal, alone or combined with other agents. Cholesterol, Merck Co. product, were given in doses of 1.2 gm per animal per day for 60 days, alone and combined with other agents.
Body weight was determined once a week during the period of experiment. Serum total cholesterol and ester were determined once every 30 days by the method of Bloor (1916).
All animals survived until the end of 60 days of cholessterol feeding were killed and the aortas were examined grossly and microscopically to determine the degree and the nature of atherosclerosis, as well as the damage produced by epinephrine,
thyroxine and vitamin D. Hematoxylin-rosin staining was applied to all cases. Colloidal-iron, aldehyde-fuchsin and oil red O stainings were applied to demonstrate acid mucopolysaccharides, elastic tissue, and lipids in selected cases.
Results and Discussion
Body weight has slightly increased during experimental period in normal control group, epinephrine treated groups, and thyroxine treated groups. But the groups treated with vitamin D showed marked decrease of the body weight, almost to one-half of the original weight.
Serum cholesterol elevated in all cholesterol-fed groups, ranging from 418 to 943mg%, cholesterol feeding alone group being the lowest and cholesterol-feeding combined with vitamin D being the highest in elevation, indicating promoting effect of vitamin D in the production of hyperholesteremia.
Gross examinations of the aortas showed marked dilatation of the aortic lumen, calcific hardening of the wall, and numerous transverse prickle formation in the aortas of the animals treated with vitamin D. The aortas of animals treated with epinephrine showed patchy slightly elevated and whitish sclerotic lesions at the intimal aspect. Atheroma formation was negligible in the groups fed cholesterol alone and cholesterol fed with thyroxine treatment. Whereas groups fed cholesterol in combination wits epinephrine or vitamin D, both of which induced changes in the
wall, stowed marked degree of atheromatous change. The atheroma in groups treated with vitamin D and cholesterol was diffues in pattern.
Microscopic examination of the arota showed linear and patchy necrotic and cicatricial change limited to the inner 1/3 of the media in epinephrine treated groups. Groups treated with vitamin D showed marked calcific degenerative changes involving inner 1/3 and middle 1/3 of the media. In either groups, there was usually narrow zone of intact tissue between degenerated media and internal elastic membrane. However, when the damage of the media was severe, the degenerative process involved the internal elastic membrane, too. The overlying intima showed mild to moderate degree of fibrous thickening. The group treated with thyroxine showed very mild histologic alteration, butt when thyroxine was given in combination with epinephrine, the damage of the media was accentuated. The groups fed with cholesterol showed various degree of atherosclerotic changes. The severity
of the changes was the least in the group fed with cholesterol alone, and was the greatest in the group fed cholesterol fellowing the treatment with epinephrine, thyroxine, and vitamin D altogether. Deposition of the lipids was observed mostly at the intima or/and neighborhood of the medial damage. But occasionally it was also present in the area where no visible medial damage was noted. When the internal elastic membrane was also damaged deposition of the lipids extended into deeper portion of the media, producing the lesion almost identical to that of atherosclerosis in human.
Histochemical examinations showed generalized as well as localized increase of acid mucopolysaccharides at the site of medial damage. Vitamin D treated groups showed marked increase of acid mucopolysaccharides mainly at and around calcific degeneration of the media. The accumulation of acid mucopolysaccharides was closely associated with the damage of elastic lamellae and also appeared to be combined with calcium which is likely attached to degenerated or intact elastic fibers. The elastic lamellae underwent various degenerative changes at the site of medial damage due to either epinephrine or vitamin D administrations. It showed swelling, splitting, disruption and finally lysis. These Changes were closely associated with accumulation of acid mucopolysaccharides. The internal elastic membrane was usually intact in the majority of the case even though the deposition of lipids in the intima was marked. But when the medial injury was extensive the internal elastic membrane was also involved allowing spread of the atheromatous process into the media.
Medial injuries were induced in the aorta of rabbits by the administration of epinephrine, thyroxine and vitamin D. Thereafter, atherosclerotic lesions were produced by excessive cholesterol feeding to investigate the effect of medial injuries on the cholesterol-fed atherosclerosis.
Intravenous injection of epinephrine regularly produced necrotic and cicatricial damage to the inner media resulting destruction of elastic fibers in various forms, and marked accumulations of acid mucopolysaccharides particularly at the site of damage.
Administration of vitamin D, on the other hand, induced marked calcific medial damage with resultant destruction of elastic lamellae and concomittant increase of acid mucopolysaccharides at the site of damage. The damages produced by epinephrine or vitamin D usually limited in the media, but when they were severe the internal elastic membrane was also involved.
Hypercholesteremia was mild in the group fed with cholesterol alone and marked in the group treated with cholesterol and vitamin D, indicating promoting effect of vitamin D on hypercholeste-ramia.
The medial damage either due to epinephrine or vitamin D intoxication, accelerated atherosclerotic process. And when the medial damage involved internal elastic membrane, atheromatous process spread into the deeper portion of the wall, which closely resembled human atherosclerosis. The mechanism of this accelerating effect of medial damage on the atherogenesis seemed to be related with the accumulation of acid mucopolysaccharides accodring to the results obtained by the present investigation.