Effects of hypertension and hyperlipidemia on the myocardium and coronary vasculature of the WHHL rabbit

Hypertension Enhances Advanced Atherosclerosis and Induces Cardiac Death in Watanabe Heritable Hyperlipidemic Rabbits

Hypertension is a major risk factor for the development of atherosclerosis. Cardiovascular risk has been reported to be significantly increased in hyperlipidemic patients with hypertension. However, it is not clear whether hypertension can directly destabilize plaques, thereby enhancing cardiovascular events. To examine whether hypertension enhances the development of atherosclerosis and increases plaque vulnerability, we generated hypertensive Watanabe heritable hyperlipidemic (WHHL) rabbits by surgical removal of one kidney and partial ligation of the other renal artery and compared the nature of aortic and coronary atherosclerosis in hypertensive WHHL rabbits with normotensive WHHL rabbits. All hypertensive WHHL rabbits died from 34 to 56 weeks after surgery, whereas no normotensive WHHL rabbits died. Pathologic examinations revealed that hypertensive WHHL rabbits showed different degrees of myocardial infarction caused by severe coronary stenosis along with myocardial hypertrophy. Furthermore, aortic lesions in hypertensive WHHL rabbits exhibited a higher frequency of intraplaque hemorrhage and vulnerable plaques than those in normotensive WHHL rabbits. These results indicate that hypertension induced by the surgical removal of one kidney and partial ligation of the other renal artery method in WHHL rabbits may not only enhance the development of atherosclerosis but also destabilize the plaques, increasing cardiac death.

Arteriosclerotic changes in the myocardium, lung, and kidney in dogs with chronic congestive heart failure and myxomatous mitral valve disease

BACKGROUND

The occurrence of small vessel arteriosclerosis in the myocardium, kidney, and lung in dogs with naturally occurring myxomatous mitral valve disease has not been previously investigated systematically.

METHODS

Twenty-one dogs with naturally occurring congestive heart failure and 21 age-matched, sex-matched, and weight-matched control dogs underwent extensive pathological and histopathological examination. Morphometry and scoring of tissue sections were used to measure arterial narrowing and fibrosis in the myocardium, kidney, and lung; and intimal thickness and plaque formation in the aorta and pulmonary artery.

RESULTS

Dogs with congestive heart failure had significantly more arterial narrowing in the left ventricle (P < .003), lung (P < .0001), and kidney (P < .02); intimal-medial thickening in the pulmonary artery (P = .04); and fibrosis in the left ventricle (P < .0001) than control dogs. However, they did not have more plaque formation or intimal-medial thickening in the aorta than controls. There was significantly more arterial narrowing in papillary muscles than in all other locations in dogs with congestive heart failure (P < .002). In control dogs, arterial changes were less pronounced and did not differ in different locations.

CONCLUSIONS

Dogs with naturally occurring myxomatous mitral valve disease have significantly more arterial changes in the myocardium, lung, and kidney, and significantly more fibrosis in the myocardium than control dogs. This could have important implications in the management of myxomatous mitral valve disease and raises interesting questions about the occurrence and importance of intramural small vessel disease in humans with primary mitral valve prolapse.

Comparison of electrocardiogram findings and lifestyles between urbanized people and ger-living people in Ulaanbaatar, Mongolia

In Ulaanbaatar, lifestyles differ between urbanized people (group A) and ger (tent)-living people (group B). Group A earn high annual incomes and live in houses or apartments. Group B (who had moved to Ulaanbaatar from nomadic areas) earn low incomes and live in narrow gers. In 2002, we investigated daily food intake, health status, and electrocardiogram (ECG) in these groups. In total, 256 subjects (group A, 142; group B, 114) were enrolled. Group A ate meat, vegetables, and fruits high enough by a Western style. Group B consumed meat but ate only small amounts of vegetables and fruits. They took a lot of fat, however, the serum lipid levels of them were not so high. The fat source as energy was plant oil for cooking rather than meat. Several abnormal ECG findings including left ventricular hypertrophy (LVH) were found in 32 (22.5%) of group A and 50 (43.9%) of group B (P < 0.001). LVH was also found more in group B than in group A. LVH in group A males was accompanied by high body weight (BW), hypertension, and high LDL-cholesterol, whereas LVH in group B males seemed to be related to an unbalanced diet, high salt intake, smoking, and some low socio-economic problems. In order to promote health condition, such risk factors should securely be eliminated from the lifestyles.

Arteriosclerosis in the influx and intravisceral arteries of the liver, kidney and lung of WHHL rabbits

We performed a histopathological investigation on arteriosclerotic development in the influx and intravisceral arteries of the liver, kidney and lung of male WHHL rabbits. In the influx arteries of these organs, we observed severe atherosclerotic vascular lesions with high-grade luminal stenosis. In the intravisceral arteries of the liver and kidney, no arteriosclerotic lesions were observed. However, in the intrapulmonary arteries, we recognized severe atherosclerotic vascular changes with high-grade stenosis or total obstruction of the lumen in some middle to large sized pulmonary arteries. These observations indicate that the development of arteriosclerosis in parenchymatous organs differs, and that some organs are predisposed to arteriosclerosis formation.

Chronic angiotensin II infusion promotes atherogenesis in low density lipoprotein receptor -/- mice

The purpose of this study was to determine the effect of chronic angiotensin II (AngII) infusion on the severity of the atherogenic process in low density lipoprotein (LDL) receptor -/- mice with established lesions. LDL receptor -/- mice receiving a diet enriched in cholesterol, saturated fat, and cholate, were infused with saline or AngII (500 ng/kg/min) for 28 days. Systolic blood pressure increased in LDL receptor -/- mice following 7 days of AngII infusion, followed by a decline to baseline levels at 28 days, despite continued AngII infusion. Serum cholesterol was not influenced by AngII infusion in LDL receptor -/- mice; however, serum triglyceride concentrations were reduced significantly in LDL receptor -/- mice receiving AngII. The percent of intimal surface area covered by lesion was not increased in LDL receptor -/- mice receiving AngII; however, the content of cholesterol (esterified and unesterified) in lesions of the arch, thoracic, and abdominal aorta was significantly increased in those mice infused with AngII. Of note, in 20% of the LDL receptor -/- mice receiving AngII, large aneurysms were found in the abdominal aorta. Aneurysms appeared as breaks in the media and surrounding tissue of the vessel wall, encompassing amorphous and acellular masses with patches of thrombotic material. These results demonstrate that chronic infusion of AngII promotes the atherogenic processes in LDL receptor -/- mice, manifest as increases in lesion cholesterol content. Effects of AngII to promote atherogenesis were apparent at doses which did not markedly elevate systolic pressure. Importantly, infusion of AngII in LDL receptor -/- mice resulted in the development of aortic aneurysms.

Effects of hypertension on hypercholesterolemia-induced changes in contraction of rabbit aorta and carotid artery

Reactivity of aortic and carotid strip from control; hypertensive; hypercholesterolemic; and hypertensive/hypercholesterolemic rabbits were studied. Maximal stress was less in strips from hypertensive/hypercholesterolemic animals. Norepinephrine sensitivity was increased in the carotid artery from hypertensive/hypercholesterolemic animals (EC50: 0.11 microM; 0.35 microM control). CaCl2 sensitivity during norepinephrine-induced contractions was enhanced by hypertension and hypercholesterolemia (carotid EC50: 0.10 mM; 0.38 mM control; aorta EC50: 0.12 mM; 0.82 mM control). Similar results were obtained during membrane depolarization. 5-hydroxytryptamine sensitivity (EC50: 0.15 microM carotid; 0.18 microM aorta) was decreased during hypertension (EC50: 0.51 microM carotid; 1.13 microM aorta) and by hypercholesterolemia (EC50: 1.76 microM carotid; 1.53 microM aorta). Our results support the hypothesis that hypertension and hypercholesterolemia increase vascular sensitivity by increasing Ca2+ permeability. Our results also suggest that hypertension and hypercholesterolemia selectively decrease 5-hydroxytryptamine-induced contractions.