Myocardial-ischemic rats (MIR). Coronary vascular alteration induced by a lipid-rich diet

Implication of hypertensive rat models for primordial nutritional prevention of cardiovascular diseases

1. Various substrains maintained during selective sib-mating contributed to the establishment of spontaneously hypertensive rats (SHR) with a variety of clinical features. 2. Stroke-prone SHR (SHRSP), developing haemorrhagic and/or ischaemic stroke spontaneously, are regarded as a model for osteoporosis. 3. The genetic mechanisms of spontaneous hypertension have been attributed pathophysiologically to neural and structural vascular alterations. 4. The mechanisms of stroke are ascribed to the limited regional oxygen and nutrient supplies to the brain areas fed by perforating arteries. 5. The genome-wide linkage analysis on the F2 obtained by crosses of SHRSP with normotensive strains has demonstrated different gene loci contributing to the development and maintenance of hypertension during the ageing process and also genes influencing the susceptibility to stroke without any effect on blood pressure. 6. Experimental studies in SHRSP revealed that stroke could be prevented by protein, Ca- or Mg-supplemented diets, particularly if given in the early stage, indicating the importance of primordial nutritional prevention of cardiovascular diseases (CVD). 7. Experimental findings in SHRSP as well as epidemiological studies on nutrition and CVD indicate the future avenue towards 'predictive-preventive medicine' for CVD.

Experimental myocardial infarction with cartilaginous and osseous metaplasia in SHR and WKY rats

Myocardial infarction was induced by ligation of the coronary artery in fifteen 32-week-old male spontaneously hypertensive rats (SHR) and fifteen 32-week-old male normotensive Wistar-Kyoto rats (WKY). Age-matched male SHR (n = 6) and WKY (n = 7) without the operation were used as non-infarcted control rats. Four weeks after the operation, cartilaginous metaplasia and osseous metaplasia were observed histopathologically in all SHR and 13 of the 15 WKY with myocardial infarction, but not in the control rats. The mean rates of infarction to the heart and the mean areas of metaplasia per rat showing metaplasia were greater in SHR than in WKY. The metaplastic areas were well correlated with the infarct percentage in SHR. It is therefore considered that extensive myocardial infarction is associated with the pathogenesis of cartilaginous and osseous metaplasia.

Overview: studies on spontaneous hypertension-development from animal models toward man

The development of genetic rat models for research on hypertension, stroke and other cardiovascular diseases (CVD) such as spontaneously hypertensive rats (SHR) and stroke-prone SHR (SHRSP) have contributed not only to the elucidation of the pathogenesis of hypertension-related CVD but also to their prediction and prevention. Since both genetic and environmental factors are involved in the pathogenesis of CVD as extensively studied so far on these models, the detection of the early pathogenic mechanisms related to the genetic factors and the control of environmental factors such as dietary improvement are useful as predictive and preventive measures against CVD. Sympathetic overresponsiveness, early development of cardiovascular hypertrophy, increased salt sensitivity and membrane or transport abnormalities in vascular smooth muscle cells (VSMC) from SHR and SHRSP, possibly related to the pathogenesis of hypertension, are so far regarded as predictors for hypertension partly applicable to human hypertension. Genetic pathogenic mechanisms of stroke in SHRSP which have been proven to be greatly influenced also by dietary factors are hypertension-induced VSMC degeneration and necrosis of intracerebral arteries due to local nutritional disturbance. One of predictors of stroke related to the pathogenic mechanisms is reduction of regional cerebral blood flow. On the other hand, the control of environmental factors, especially nutrition and diets such as intakes of animal and vegetable proteins, some amino acids and fatty acids, potassium, calcium, magnesium, dietary fibers, etc., have been experimentally demonstrated to be effective for the prevention of CVD in these genetic models, and the applicability of these experimental findings to the CVD prevention in man is now supported from our world-wide epidemiological studies (WHO CARDIAC Study).

Experimental intervention of hypertension and cardiovascular diseases

Experimental prevention of hypertension and related cardiovascular diseases has been studied in rat models for hypertension and stroke and not only salt reduction but also increased intakes of potassium, calcium, magnesium, protein, some amino acids and fatty acids and dietary fibers have been proven to be effective and indicated the importance of nonpharmacological dietary prevention of cardiovascular diseases. These experimental findings contribute to dietary risk factor analyses and the prevention of hypertension and its complications in man, as demonstrated by a cross-sectional epidemiological study on cardiovascular diseases and alimentary comparison (WHO-CARDIAC Study).

Predictive and preventive pathology of cardiovascular diseases

The development of genetic models for research on hypertension and stroke, spontaneously hypertensive rats (SHR) and stroke-prone SHR (SHRSP), have contributed not only to the elucidation of the pathogenesis of hypertension-related cardiovascular diseases (CVD) but also to their prediction and prevention. Since both genetic and environmental factors are involved in the pathogenesis of hypertension and stroke in SHR and SHRSP, the detection of the genetic factors and the control of environmental factors have been proven to be useful as predictive and preventive measures against hypertension and related CVD. Early rise in blood pressure, sympathetic overresponsiveness, early development of cardiovascular hypertrophy, increased salt-sensitivity and membrane abnormalities detected in vascular smooth muscle cells (VSMC) from SHR and SHRSP, which are related to the pathogenesis of hypertension, have been examined for their applicability to the prediction of hypertension in man. Pathogenic mechanisms of stroke in SHRSP have been studied by electron microscopy, and VSMC degeneration and necrosis were noted to start at the outer media of intracerebral arteries which were exposed to local hypoxia and hyponutrition due to limited diffusion through the blood-brain barrier. Macrophages are involved in the process of arterionecrosis with fibrin deposition in SHRSP, and their involvement has also been proven immunohistochemically in human autopsy cases. Moreover, reduction of regional cerebral blood flow, hypoxic vulnerability of the brain detected by the NMR technique and additional cellular abnormalities such as membrane fragility and accelerated lipid incorporation may possibly be applied to the prediction of stroke and atherosclerotic diseases in man. On the other hand, experimental control of cellular, neural and vascular mechanisms of hypertension and stroke in these animal models have been proven to be effective for the prevention of CVD not only pharmacologically but also non-pharmacologically by dietary sodium reduction, and increased intake of potassium, calcium, protein and dietary fiber. The applicability of dietary control of hypertension and stroke to humans has been supported by our epidemiological studies in Japan as well as by the WHO-coordinated international cooperative study on cardiovascular diseases and alimentary comparison (WHO CARDIAC study). These new experimental and epidemiological findings are extending new horizons in medicine, where the main medical activity should be focused on the prediction of diseases by detecting genetic disposition as well as on prevention by the control of environmental factors.

Dexamethasone suppression of cushingoid degenerative changes in obese spontaneously hypertensive rats (SHR)

Male and female, young (2 months old) and mature (10 months old), obese and nonobese, spontaneously hypertensive rats (SHR) were treated with dexamethasone, 5 micrograms/rat and 10 micrograms/rat, respectively, subcutaneously (SC) 2 times daily for 5 months. Steroid treatment stilled the voracious appetite of the obese SHR, and the massively obese, mature animals were reduced to almost normal size. The young, steroid-treated, obese SHR did not develop their genetically programmed corpulency. The untreated, young and mature, obese SHR ate voraciously, became massively obese, and developed their characteristic Cushing's disease-like spectrum of degenerative changes, eg, hypertension, hyperlipidemia, hyperglycemia, muscle wasting, kidney stones, thin skin, and accelerated aging. The blood pressure of the steroid-treated animals was lowered concomitant with reduced levels of circulating ACTH, beta endorphin, insulin, triglycerides, and cholesterol. Dexamethasone caused hyperlipidemia, hyperglycemia, and increased BUN levels in young obese and nonobese SHR only. The mature obese SHR had giant-sized thymus glands that were further enlarged with steroid treatment; dexamethasone was thymolytic in young, obese and nonobese SHR. Dexamethasone caused severe reduction of pituitary and adrenal gland size, simulating the condition of hypophysectomy. These findings demonstrate that dexamethasone suppression of the pituitary-adrenal axis palliates and prevents the spontaneous development of Cushingoid degenerative changes in these genetically obese and hypertensive rats.