Bernard C. Wexler

Spontaneous arteriosclerosis in repeatedly bred male and female rats

Summary Repeatedly bred male and female rats of several strains develop arteriosclerosis spontaneously. The arterial lesions in the male breeder rats remain microscopic while the arteriosclerosis becomes grossly recognizable in the female breeder. The incidence and severity of the arterial damage is enhanced with each breeding. The lesions appear first in the abdominal aorta and spread to the arch and thoracic portions. Later, as arteriosclerosis becomes well established the coronary, renal and cerebral arteries also develop arterial lesions. A large variety of degenerative arterial changes have been found which are believed to represent early and advanced lesions as well as various stages of repair and degeneration. It has also been found that there are specific morphological reactions peculiar to certain segments of the aorta. The most frequent lesion encountered, in both sexes, is a focal subintimal accumulation of mucopolysaccharide followed by scarring. In these same sites the media shows pooling of mucopolysaccharide and swelling and eventual fracture of elastic fibers. This type of lesion is also found in male breeders. However, the male breeder frequently develops an additional lesion consisting of intense focal mesenchymal cell infiltration of the intima. These cells become enlarged and intensely basophilic, develop a resemblance to cartilage cells, and ultimately may undergo cartilaginous metaplasia. The gross and histological aspects of the pathogenesis of this type of arteriosclerosis is identical in breeder rats of all of the strains examined thus far. Virgin rats of comparable age do not develop arterial lesions. Repeated breeding is the one outstanding factor which appears to be best correlated with the development of the arterial disease.

Myocardial Necrosis in Rats: Serum Enzymes, Adrenal Steroid and Histopathological Alterations

Acute infarctoid myocardial necrosis has been produced in virgin rats by injection of isoproterenol. The lesions are essentially identical, both grossly and microscopically, with naturally occurring acute infarcts which we have observed in arteriosclerotic breeder rats. During the establishment of drug-induced necrosis the animals displayed signs of shock and congestive heart failure. Serum transaminases and lactic dehydrogenase levels underwent changes which coincided with the establishment and repair of the myocardial damage. The male rats had a higher mortality rate than the females. The male rats also developed more massive myocardial necrosis and showed a decreased capacity to repair myocardial damage. The adrenal glands became greatly hypertrophied and the thymus became severely involuted coincident with the acute establishment of the myocardial lesion. In vitro studies indicated that changes in adrenal function also accompanied the acute onset of myocardial destruction. The adrenal hypertrophy decreased during recovery from shock and during repair of the lesion.

Degenerative Changes in the Cardiovascular System of the Spawning Pacific Salmon (Oncorhynchus tshawytscha)

In a stndy of the cardiovascular system of spawning Pacific salmon, degenerative changes were found in the heart muscle, coronary and visceral arteries, and capillaries of the kidney glomeruli. The heart muscle showed vacuolization of the muscle fibers with loss of fibrils, deposition of collagen, and cartilaginous meta plasia. Changes in the coronary and visceral arteries consisted of intimal hyperplasia with deposition of mucopolysaccharides, disruption of the internal elastic membrane, and destruction of adjacent muscle fibers in the media. The glomerular capillaries showed marked sclerosis. The resemblance of the arterial changes in the salmon to the beginning mani festations of arteriosclerosis in man, mammals, and birds is pointed out, and the relationship of the salmons state of hyperadrenoeorticism to the occurrence of the vascular lesions is discussed.

Myocardial infarction in young vs old male rats: Pathophysiologic changes

Young (90 days) and old (15 months) male, Sprague-Dawley rats were subjected to an acute and massive myocardial infarct by giving them two injections of a large dose of isoproterenol. The animals were autopsied at sequential time intervals to ascertain the similarities or dissimilarities in the pathophysiologic events which attend acute myocardial infarction and repair in young vs old rats. Although the signs and severity of hypotensive shock appeared to be equal, mortality was higher in the old rats, especially during the acute necrosis phase. The older rats also manifested more severe and persistent congestive heart failure, i.e., hydrothorax. Serum enzymes (CPK, SGOT, SGPT, and LDH), lipids (triglycerides, free fatty acids, and cholesterol), glucose, and BUN levels manifested a dynamic rise and fall concomitant with the induced myocardial necrosis and repair phases with distinct differences in these metabolic changes between young and old rats. Despite initially higher circulating levels of corticosterone in the old vs young rats, the older animals manifested little or no increase in circulating corticosterone levels during the acute stress of myocardial infarction. This apparent lack of adrenocortical responsiveness was accentuated by the concomitant finding of greatly hypertrophied, hemorrhagic, and lipid-depleted adrenal glands in the old rats vs a dynamic increase in circulating corticosterone levels and alterations in the weight of adrenal and thymus glands of the young rats. During the myocardial repair phase, the young rats manifested extensive endocardial fibrosis whereas the old rats displayed little or no endocardial fibrosis but copous and persistent myocardial edema and ground substance in keeping with their higher concentration of cardiac hexosamine. The pathophysiologic course of events which attends myocardial necrosis and repair is quite different in young vs old rats and may be related to the degree of responsiveness of the pituitary-adrenal axis which changes with age.

Spontaneous Coronary Arteriosclerosis in Repeatedly Bred Male and Female Rats

Repeatedly bred male and female rats of several strains develop arteriosclerosis spontaneously, irrespective of diet. The severity of the lesions differs between male and female breeders. The morphology and pathogenesis of these lesions have been found to be the same in all of the strains examined. Once the process of arteriosclerosis has been initiated within the abdominal aorta, the subendocardial and medium-sized myocardial coronary arteries also show degenerative changes. The large epicardial coronary arteries become arteriosclerotic only when the process of arteriosclerosis has become severe and generally distributed throughout the aorta. The smaller subendocardial lesions are characterized by occlusive swelling of medial muscle cells and by the presence of vacuoles. These vacuoles react negatively to lipid stains but stain positively for mucopolysaccharide. The myocardial arteries show endothelial hyperplasia, elastosis and accumulations of mucopolysaccharides, especially in the region of fragmented elastic elements. The mucopolysaccharide-rich endothelial cushions eventually become fibrosed. The epicardial arteries show intense accumulations of calcium-mucopolysaccharide complexes. These arteries become greatly distended and can be detected grossly because of their size and tortuosity. Acute and chronic myocardial infarct-like lesions are found but these cannot be associated with specific coronary thrombi or arteriosclerotic lesions. Valvular scarring, calcification of the papillary muscles and disappearance of myocardial mast cells has been correlated with advancing arteriosclerosis. The relation between the intensity of coronary arteriosclerosis and the frequency of breeding, the sex of the animal, and the strain indicates that the pathogenesis of this disease in breeder rats is probably governed by hormonal factors, e.g., sex and adrenal steroids, as well as by genetic factors.

Spontaneous Arteriosclerosis of the Mesenteric, Renal, and Peripheral Arteries of Repeatedly Bred Rats

Repeatedly bred male and female rats develop arteriosclerosis spontaneously. The arteriosclerosis appears to be accelerated by breeding because virgin rats of comparable age do not develop arterial disease. The arterial lesions begin in the abdominal aorta and consist of subendothelial swelling, mucopolysaccharide accumulation and eventual fibrosis. With continued, active breeding, the arterial lesions continue to increase in severity in the abdominal aorta, becoming grossly visible in the female breeder and of microscopic proportions in the male breeder. Concomitant with the increasing severity of arteriosclerosis in the abdominal aorta, the mesenteric arteries and the visceral branches also show increasing numbers of arterial lesions. The lesions in the mesenteric and visceral branches are of varied morphology. The main renal artery, for example, shows fibromuscular dysplasia, its hilar portion displays intimal basophilia and elastosis and the intrarenal branches develop intimal cushions. The male breeder develops severe, grossly visible lesions in the proximal portions of the iliac arteries, the lesions becoming less complex distally. The female breeder shows no grossly visible lesions in the iliac arteries but arteriosclerosis is severe throughout the length of the arteries to the extremities, the severity of these lesions being proportional to the arteriosclerosis in the abdominal aorta and its branches.

PROTECTIVE EFFECTS OF PROPRANOLOL ON ISOPROTERENOL- INDUCED MYOCARDIAL INFARCTION IN ARTERIOSCLEROTIC AND NON-ARTERIOSCLEROTIC RATS.

Abstract Male and female, arteriosclerotic and non-arteriosclerotic rats were treated with the anti-lipemic agent, clofibrate, for 8 days and then subjected to an acute myocardial infarction by injecting them with two large doses of isoproterenol spaced 24 hours apart. The animals were killed at sequential time intervals during the acute necrosis and early repair phases of myocardial infarction. Pre-treatment with clofibrate caused a definite improvement in survival, less shock and prostration, and ECG evidence of little or no ischemia. Increased SGOT levels, hepatic lipid and necrosis were indicative of advanced liver damage. Although clofibrate-treated animals showed little change in serum lipids during the acute cardiac necrosis phase, they were hyperglycemic and showed the greatest increase in BUN levels. Clofibrate-treated animals had higher serum corticosterone levels than those given isoproterenol alone. Despite superior survival rates, both the arteriosclerotic and non-arteriosclerotic, clofibrate-treated animals exhibited equally severe histopathologic evidence of myocardial damage. It is suggested that the protective effect of prophylactic treatment with clofibrate against isoproterenol-induced myocardial infarction in rats may be due to its ability to change corticosterone levels in the circulation.

Carotid and cerebral arteriosclerosis in the rat.

Male and female breeder rats spontaneously develop arteriosclerosis. This occurs first in the aorta and coronary arteries and subsequently in the carotid and intracranial arteries. The carotid arteries show mesenchymal cell proliferation in the media followed by subintimal swelling and mucoid deposition, elastosis, cartilaginous metaplasia and eventual bone formation. Lipid deposition occurs infrequently, and then only in advanced lesions in the media. Severe lesions are much more frequent in the female breeder and the tendency towards cartilaginous metaplasia and bone formation is peculiar to the carotid arteries. The cerebral arteries show little arteriosclerotic involvement except for aneurysm-like outpouchings of the internal elastic membrane associated with mucopolysaccha-ride accumulation about the sites of elastic tissue disruption. Despite severe fulminating arteriosclerosis in the carotid arteries, the cerebral arteries and the brain tissue itself show little or no significant evidence of degenerative change. These results are interpreted to mean that the cerebral arteries of the breeder rat follow a different physiological and morphological pattern of response than the rest of the arterial system.

Serum creatine phosphokinase activity following isoproterenol-induced myocardial infarction in male and female rats with and without arteriosclerosis

Abstract Male and female rats with and without arteriosclerosis were given two subcutaneous injections of isoproterenol spaced 24 hours apart. The animals promptly developed signs of shock and prostration and myocardial infarction. Sequential sacrifice of the animals at hourly intervals after each of the injections of isoproterenol demonstrated that there was a prompt and marked increase in serum creatine phosphokinase (CPK) activity commensurate with the destruction of myocardial tissue. Serum CPK levels were elevated long before microscopic examination of the myocardium could demonstrate any evidence of overt muscle damage, indicating that the enzyme CPK is a sensitive index of not only myocardial necrosis but of sarcolemmal membrane permeability as well. The changes in serum CPK levels were much more dramatic in these experiments than in previous experience where other serum enzymes were used to detect myocardial infarction, e.g., transaminases (SGOT and SGPT) and lactic dehydrogenase. Female rats showed much more severe untoward signs in connection with myocardial infarction than males. Yet the female subjects survived in much greater numbers and showed much more rapid and effective repair of the heart than the male subjects. This dichotomous response between the sexes was also reflected in the pattern of the CPK response. Animals having pre-existing arteriosclerosis prior to being subjected to isoproterenol-induced myocardial infarction show greater excursion of their serum CPK levels than animals with normal arteries. However, the presence of severe arteriosclerosis per se in no way contributed to serum CPK levels. Therefore, it is suggested that the extra elevation of serum CPK levels in arteriosclerotic animals is a reflection of greater intrinsic damage to the myocardium in such subjects despite the fact that they manifest less severe evidence of shock and heart failure than subjects with normal arteries. Heart weight is greatly increased during the acute episode of myocardial infarction with marked oscillations in weight on an hour-by-hour basis. Histologic and other evidence indicates that this increase in cardiac size and weight is due to cellular infiltration, edema and possible myocardial electrolyte abnormalities, and increased sarcolemmal membrane permeability.

Myocardial necrosis induced by isoproterenol in rats. Changes in serum protein, lipoprotein, lipids and glucose druing active necrosis and repair in arteriosclerotic and nonarteriosclerotic animals.

From The May Institute for Medical Research, Jewish Hospital and Departments of Pathology and Biological Chemistry, University of Cincinnati College of Medicine, Cincinnati, Ohio. Supported by grants from the Southwestern Ohio Heart Association and by Grants HE-8868, HE-8813 and HE-6315 from the National Heart Institute and a General Research Support Grant (FR-5633), United States Public Health Service. * Research Career Program Award (HE-K3-1734) from the National Heart Institute, United States Public Health Service. t This work was performed during the tenure of an Advanced Research Fellowship from the American Heart Association. Present address: Oregon Regional Primate Center, Beaverton, Oregon. In previous reports we have described various pathophysiologic changes which occur in nonarteriosclerotic virgin rats and arteriosclerotic breeder rats during the acute onset and repair of myocardial necrosis.I-3 The nonarteriosclerotic virgin rats display a much more severe reaction to the stress of drug-induced cardiac necrosis than the breeder rats with pre-existing arteriosclerosis. In addition to a greater mortality rate, nonarteriosclerotic rats also show much greater cha,nges in their serum glutamic acid transaminases, both oxalopyruvic and pyruvic (SGOT and SGPT) and lactic dehydrogenase (LDH) levels during the acute onset and repair of myocardial necrosis.3 Analyses in vitro of the aketolic adrenal steroid production patterns of animals undergoing cardiac destruction and repair also demonstrated marked differences in the steroid patterns between nonarteriosclerotic and arteriosclerotic rats.2 The adrenocortical steroidogenic patterns and the gravimetric and histopathologic changes in the adrenal and thymus glands of these animals indicated that there is an intense