Effects of diet and metoprolol on lipid levels in the blood plasma and morphology of the heart and intramural branches of coronary arteries of spontaneously hypertensive male rats. A 9-month study

Semipurified diets containing 0.5% cholesterol were used in a 9-month study with spontaneously hypertensive male rats to characterize the effects of the protein source (casein vs. soybean protein), and the selective beta 1-adrenoceptor antagonist metoprolol on both lipid levels in blood plasma and the aorta, and on the morphology of intramural branches of coronary arteries. Raised blood lipid levels were observed in these rats. A significant decline in HDL2 cholesterol took place, while plasma cholesterol belonging to lipoprotein fractions of lower density increased. Metoprolol treatment led to a substantial elevation of the plasma triacylglycerol level and, with time, a reduced cholesterolemic response. The use of soybean protein instead of casein had a persistent plasma lipid-lowering effect. Arteriosclerotic changes in the form of musculo-elastic thickenings, intimal cushions and homogeneous hyalin deposits appeared in the intramural coronary arteries of rats in all groups after 9 months on the diet. However, intimal deposition of lipid was only present in rats belonging to the casein group not treated with metoprolol. Rats of this group also showed more severe myocardial lesions in the form of scar tissue with or without inflammatory cell reaction.