외상 cortisone 및 vitamin C가 cholesterol 식이성 가토동맥경화증에 미치는 영향
Effects of mechanical trauma, cortisone and vitamin C upon atherosclerosis in cholesterol-fed rabbits
Despite innumerable studies, the etiology and pathogenesis of atherosclerosis remain obscure. Previous investigations in our department(Kim 1961, Shin 1963, Huh 1965, Oh 1965) demonstrated that deficiency of pyridoxine and essential fatty acids, hypertension, and medial damage of the aorta promoted the development of experimental atherosclerosis in animals, and, in the various stages of atherosclerosis, ground substance of the aortic wall, namely acid mucopolysaccharides, seemed to play an important role in atherogenesis.
During the past half a century studies of experimental atherosclerosis were concentrated on cholesterol-induced atherosclerosis. The lesion produced by excessive cholesterol feeding resembled that observed in human disease. However, it was soon learned that there are as much disimilarities as similarities between atherosclerosis in human and in cholesterol-fed experimental animals. Therefore, it was thought that there must be factors other than only a lipid disturbance is in the development of human atherosclerosis.
Among many possible factors, those of loca disturbances in the arterial wall have been studied and stressed by several investigators. These local facotrs include disturbance of endothelium(Friedman and Byers 1963), medial damage(Duff 1936,
constantinides et al. 1958, Hass et al. 1961, Oh 1965), alteration in the internal elastic membrane(Taylor et al. 1963), disturbance of the normal filtration process of the vessel wall(Page 1954), alteration of ground substance(Farber 1949,
Bertelsen 1963), and difference in local hemodynamics(Texon 1963). Various toxins, chemical agents and physical means have been used in the study of these local factors.
The preseet investigation is designed to study the effects of direct mechanical trauma on the aortic wall, and the influence of trauma on cholesterol-fed atherosclerosis. At the same time, the effects of cortisone and vitamin C upon the traumatic injury site and on the subsequent atheroma formation have been studied.
Direct mechanical trauma was produced by clamping the aortic wall with a hemostat, an effect which is present during vascular surgery.
Materials and Methods
Eight albino rabbits, around 2 kg. in weight, were divided into 10 groups and treated as follows:
Group Ⅰ was given cholesterol diet only; Group Ⅱ was subjected to clamping injury only' Group Ⅲ was fed cholesterol following the clamping injury to the aortic wall; Group Ⅳ was given cholesterol and cortisone together; Group Ⅴ was given cortisone following the clamping injury to the aorta; Group Ⅵ was given cholesterol and vitamin C together; Group Ⅶ was given vitamin C following the clamping injury to the aorta; Group Ⅷ was given cholesterol and cortisone following the clamping injury to the aorta; Group Ⅸ was given cholesterol and vitamin C following the clamping injury to the aorta; and Group Ⅹ was used as untreated normal control.
Basic diet consisted of 300 gms. of natural grass diet per animal per day, except 7 animals were fed with bean curd residue to compare the effect of natural grass diet and bean curd residue on the dietary hypercholesterolemia. Cholesterol was the product of Merck Co. and given 1.2gm. per animal per day for 20 to 120 days.
Cortisone was the product of the North American Laboratory and was prepared in the form of cortisone acetate. It was given in doses of 10 mg. per animal per day intramuscularly. Vitamin C was give 10 mg. per animal per day orally. After the abdominal aorta was exposed retroperitoneally under ether anesthesia, the clamping injury was produced at three points in the abdominal aorta between the renal arteries and the iliac bifurcation by a single clamping of a hemostat.
Animals were killed at the various ietervals during the 120 day experimental period. The aortas were dissected, and gross and microscopic examinations of the injured areas and aortic atherosclerosis were made. For the microscopic examination, hematoxylin-eosin, Verhoeff van Gieson, van Gieson, aldehyde-fuchsin, phosphotungstic acid hematoxylin, colloidal-iron, Sudan Ⅳ, and oil red O stainings were made.
Serum cholesterol determination was carried out once every 30 days and the body weight was measured evey 10 days.
Body weight increased slightly in all groups without there being any significant difference between each groups.
The level of total serum cholesterol ranged from 39.2±11.9mg% to 79.4±15.6mg% in the normal control group. It was elevated in all groups fed with cholesterol, but the highest elevation was observed in group Ⅲ (cholesterol feeding after the clamping injury), and the least slevation in group Ⅳ(cholesterol feeding together with cortisone treatment). The administration of vitamin C did not notably influence the level of serum cholesterol, but feeding a bean curd residue promoted hypercholesterolemia. Sixty days after the beginning of cholesterol feeding, the elevation of serum cholesterol level was the highest. Thereafter it gradually
decreased in spite of continuous choclesterol feeding. the level of the ester form also parallelled the increase of total cholesterol.
Gross examination of the aorta revealed smooth intima with an uniform elasticity of the aortic wall in the normal control group. The groups subjected to the clamping injury on the aorta showed transverse grooves with elevated margins at the site of clamping.
Cholesterol feeding produced various degrees of atheromatous change particularly at the ascending portion and the arch of the aorta. The greatest degree of atheromatous change was observed in the group fed with cholesterol following the clamping injury to the aorta. The atheroma formation in this group was not limited
only to the ascending portion of the aorta, but also there was a marked amount of atheromatous changes observed in the abdominal aorta, particularly at the site of the trauma.
The administration of cortisone prevented the development of atheroma, but, the following of vitamin C, only a slight inhibiting effect on atheroma formation was noted.
Microscopic examination revealed trasmural damage to the aorta involving entire thickness of the wall at the sites of clamping injury. The damage was most noted in the muscular and elastic fibers. The muscular element soon started to regenerate and finally spread over the adjacent intima. the damage to the elastic fibers resulted in a focal complete disruption of the internal elastic membrane and elastic fibers in the media. The damage to the elastic fibers lasted throughout the 4 month experimintal period. The direction of the elastic fibers became irregular as hyperplasia of the muscular elements took place. The connective tissue element and collagenous fibers appeared in small amount at the the injured areas, and the amount of acid mucopolysaccharide increased slightly during the reparative process.
The administration of cortisone suppressed regeneration and hyperplasia of the muscular and fibrous elements at the sites of injury, but vitamin C did not appear to have any effect.
Cholesterol induced various degrees of atheromatous changes, which were concentrated at the injured sites. The deposition of lipids was limited to the intima at the intact part of the aortic wall, whereas at the sites of injury it penetrated deep into the media. The deposition of lipids was also greater at the lower margin of the wound, where the overgrowth of the intima was more pronounced.
Clamping of the aorta produced transmural crushing injury to all elements of the aortic wall. Smooth muscle regenerated rapidly and spread over the adjacent intima.
Damage to the elastic fibers, on the other hand, lasted longer and a complete regeneration was not achieved during the 4 months period of the experiment.
Cholesterol feeding following clamping injury to the aortic wall produced a concentration of atheroma formation at the site of injury, and the lipid deposition penetrated deep into the media. The mechanism which concentrate atheroma formation at the injured areas appeared to be related to a hyperplesia of fibro-muscular tissue in the reparative process of the wound. At the same time a local alteration of hemodynamics created by grooves and eminences at the sites of injury seemed to influence the elective deposition of lipids, particularly in view of the fact that lipids were deposited in greater concentration at the lower margin of the wound.
The cortisone caused an inhibition of the development of atherosclerosis. This effect appeared to be due to a suppression of mesenchymal hyperplasia during the healing process of the wound and also suppression of hypercholesterolemia. On the other hand, the administration of vitamin C did not significantly influence either the atheroma formation or hypercholesterolemia.