No abstract

A HF/HC diet in mice results in significant aortic valve abnormalities. Putting WT mice on a HF/HC diet reproduced a combination of atherogenic factors (obesity, mild dyslipidemia, and hyperglycemia) more commonly encountered in humans than isolated severe hypercholesterolemia. Severe hypercholesterolemia was not a prerequisite in our model. This experimental model suggests that AS development is multifactorial and that hypercholesterolemia should not be the only target in this disease.

Background-Past studies have suggested that the adrenergic system becomes abnormally activated in chronic volume overload, such as in severe aortic valve regurgitation (AR). However, the effectiveness of agents directed against this adrenergic activation has never been adequately tested in chronic AR. We therefore tested the effects of metoprolol treatment on the left ventricular (LV) function and remodeling in severe chronic AR in rats. Methods and Results-Severe AR was created in adult male Wistar rats by retrograde puncture of the aortic leaflets under echocardiographic guidance. Two weeks later, some animals received metoprolol treatment (25 mg/kg) orally for 24 weeks, and some were left untreated. LV dimensions, ejection fraction, and filling parameters were evaluated by echocardiography. Hearts were harvested at 1, 2, 14, and 180 days for the evaluation of hypertrophy, ␤-adrenergic receptor status, and extracellular matrix remodeling. We found that metoprolol treatment prevented LV dilatation and preserved the ejection fraction and filling parameters compared with untreated animals. Metoprolol increased the expression of ␤ 1 -adrenoreceptor mRNA and reduced G protein receptor kinase 2 levels. Collagen I and III mRNA levels were reduced. Cardiac myocyte hypertrophy was also prevented. Conclusions-In our experimental model of severe AR, metoprolol treatment had a significant beneficial global effect on LV remodeling and function. These results suggest that the adrenergic system is important in the development of volume-overload cardiomyopathy in AR and that adrenergic-blocking agents may play a role in the treatment of this disease.

The objective of this study was to assess the long-term effects of beta-blockade on survival and left ventricular (LV) remodeling in rats with aortic valve regurgitation (AR). The pharmacological management of chronic AR remains controversial. No drug has been definitively proven to delay the need for valve replacement or to affect morbidity and/or mortality. Our group has reported that the adrenergic system is activated in an animal model of AR and that adrenergic blockade may help maintain normal LV function. The effects of prolonged treatment with a beta-blocker are unknown. Forty Wistar rats with severe AR were divided into 2 groups of 20 animals each and treated with metoprolol (Met, 25 mg.kg(-1).day(-1)) or left untreated for 1 yr. LV remodeling was evaluated by echocardiography. Survival was assessed by Kaplan-Meir curves. Hearts were harvested for tissue analysis. All Met-treated animals were alive after 6 mo vs. 70% of untreated animals. After 1 yr, 60% of Met-treated animals were alive vs. 35% of untreated animals (P = 0.028). All deaths, except one, were sudden. There were no differences in LV ejection fraction (all >50%) or LV dimensions. LV mass tended to be lower in the Met-treated group. There was less subendocardial fibrosis in this group, as well as lower LV filling pressures (LV end-diastolic pressure). beta-Adrenergic receptor ratio (beta(1)/beta(2)) was improved. One year of treatment with Met was well tolerated. Met improved 1-yr survival, minimized LV hypertrophy, improved LV filling pressures, decreased LV subendocardial fibrosis, and helped restore the beta-adrenergic receptor ratio.