Cholesterol 식이성 家兎동맥경화증의 소장에 관한 연구

Abstract

[한글]

[영문]

Experimental studies on atherosclerosis during past half a century have been focused on the production of the lesion similar to that of human atherosclerosis.

The most significant achievement through these studies is the experimental induction of cholesterol-fed atherosclerosis in rabbits. Development of atheroma in cholesterol-fed rabbits is attributed to the marked hypercholesterolemia following the cholesterol feeding. But many other factors besides hypercholesterolemia, such as local factors of the vascular wall and disturbances of balance among different kinds of lipids in the serum also play the important role.

Farber(1949), Moon and Rinehart(1952) and Bertelsen(1963) claimed importance of increased acid mucopolysaccharides for the initiation of lipids deposition in the vascular wall, while Constantinides et al. (1958) and Hass et al. (1961) stressed

intimal proliferation for the deposition of lipids and local changes of the vascular wall.

Knowledge on the prevention and evolution of atheroma is equally important as the induction of atheroma for the understanding of atherosclerosis. However, very little works have been reported in these subjects. Duff(1936) and Constantinides et

al.(1958) reported that cholesterol-induced atheroma in the rabbots will progressively increase even after the discontinuation of cholesterol feeding.

Friedman and Byers(1963) reported that cholesterol-induced atheroma in the rabbits will regress after serum cholesterol returned to normal following the discontinuation of cholesterol feeding. Recently Bortz(1968) reported that if cholesterol feeding stopped when serum cholesterol level reaches around 1,000mg%, amount of lipids in the aortic wall will decrease accompanied by the decline of serum cholesterol level. These reports contradict each other and require further clarification.

The present investigation is aimed to evaluate a span of cholesterol-fed atheroclerosis in rabbits from its changes of elastic fibers and acid mucopolysaccharides as well as the alteration of different fractions of serum lipids.

Materials and Methods

Albino rabbits weighing around 2.0㎏ were divided into three major experimental group and treated as follows.

Group Ⅰ : Normal untreated control

Group Ⅱ : Cholesterol feeding

A : Cholesterol feeding for 15days

B : Cholesterol feeding for 30days

C : Cholesterol feeding for 45days

D : Cholesterol feeding for 60days

Group Ⅲ : Discontinuation of cholesterol feeding after 60 days of cholesterol feeding

A : Discontinuation for 15days

B : Discontinuation for 30days

C : Discontinuation for 45days

D : Discontinuation for 60days

E : Discontinuation for 75days

Animals in groups Ⅱ and Ⅲ were subdivided and killed at 15days of intervals.

Group Ⅰ and each subgroup in group Ⅱ and Ⅲ consisted of 10 animals. Cholesterol was given a dose of 1.5gm per animal per day at early in the morning. Basic diet consisted of bean-curd residue and was given 300gms per animal per day. Animals

were killed by air embolism at the end of subjected experimental period. A blood sample was taken before the animal was killed to determine serum total and free cholesterol and phospholipids. Cholesterol determination was made by the method of Schoenhiemer and Sperry(1934) and phospholipid by the method of Youngberg(1930).

The aorta from each animal was examined grossly to determine the degree of atheroma formation after Sudan-Ⅳ staining on gross specimen. Then two sections each from the ascending, thoracic and descending portions of the aorta were taken to examine histologic alterations, especially degree of coronary atherosclerosis and lipids deposition in the liver. All sections were stained by hematoxylin and eosin routinely, and special stainings included Verhoeff-Van Gieson method for elastic tissue, alcian blue for acid mucopolysaccharides, and oil red-O for lipids.

Results and Summary

Serum cholesterol and phospholipid rose rapidly following the cholesterol feeding and reached to the peak level at 45 days of feeding, followed by slight decline even though cholesterol feeding was continued. The rise of serum lipids was mainly due to the rise of free cholesterol although other fractions were increased as well. Discontinuation of cholesterol feeding after the feeding of 60 days did not bring significant decrease of serum lipids level until the 75th day. As the level of serum lipids elevated, the ratio of phospholopid to total or free cholesterol became inverted and remained so even after the discontinuation of cholesterol feeding.

The degree of aortic atheroma was negligible until the 30days of cholesterol feeding, but it increased abruptly at the 45th day cholesterol feeding, followed by gradual increase at the 60th day. Discontinuation of cholesterol feeding did not bring decrease in severity of atheroma but showed rather increase or sustained severity on gross examination. The microscope examinations of the aortas showed focal degeneration of internal elastic membrane and adjacent elastic fibers accompanied by accumulation of acid mucopolysaccharides. Deposition of stainable

lipid did not accumulate until the 45th day of cholesterol feeding. Lipid deposition initiated as accumulation of lipid laden cells at the intima where focal alterations of elastic fibers and accumulation of acid mucopolysaccharides preceded. As the cholesterol feeding continued, the degree of lipid accumulation of acid mucopolysaccharides preceded. As the cholesterol feeding continued, the degree of lipid accumulation, degeneration of elastic tissue and accumulation of acid mucopolysaccharides increased. The accumulated lipids were mostly localized within cells at the intima. After the discontinuation of cholesterol feeding, lipids laden cells of intima became disintegrated resulting into free lipids droplets in the extracellular area associated with appearance of newly formed collagen fibers. As the time passed, lipid laden cells of atheroma disintegrated entirely and the atheroma was gradually replaced by acid mucopolysaccharides, rich collagen fibers

and finally newly formed fine elastic fibers begun to appear at the 60th day after discontinuation of cholesterol feeding.

At the 75th day the atheroma turned into fibrous plaque with very little amount of lipid droplets. While pre-existed atheroma transformed gradually to a fibrous plsque, fresh accumulation of new lipid laden cells at the luminal aspect was also observed, resulting into widening of surface areas of atheroma. Therefore, if the feeding of cholesterol is discontinued, preformed atheroma will undergo fibrous transformation in one hand while formation of new athroma continues on the top of degenerating one as long as the serum cholesterol level remain elevated.

The degree of lipid deposition in the liver closely paralleled to that of aortic atheroma, but the development of atheroma in the coronary arteries was very slow and enhanced rather after the discontinuation of cholesterol feeding.

The data obtained by present investigation indicated that focal damages of aortic wall and accumulation of acid mucopolysaccharides preceeds the deposition of lipids will continue even after the cholesterol feeding was discontinued as long as serum lipids concentration remain elevated although preformed athroma undergoes gradual transformation into fibrous plaque.