Effects of Diet and Metoprolol on Lípid Levels in the Blood Plasma and Morphology of the Heart and Intramural Branches of Coronary Arteries of Spontaneously Hypertensive Male Rats

Abstract

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 Β₁-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.

Comparison of Dietary Casein and Soybean Protein Effects on Plasma Lipid and Gastrin Levels, Hepatic Δ^6-Desaturase Activity and Coronary Arteriosclerosis in Male Sprague-Dawley Rats

“…It is also clear that the dietary protein-dependent difference in plasma cholesterol persists throughout a 9-rnonth period. In an analogous 9-month ex periment with SHR fed on the same type of diets, including the same type of dietary fat, as used in the present experiments, plasma cho lesterol levels were maintained at approxi mately 3 mmol/1 throughout the experiment [1], In the present experiments, plasma cho lesterol levels observed in casein-fed rats were consistently 2-3 times higher than those ob served in the SHR [1], while values presently observed in soybean protein-fed rats were raised by approximately 40-70% above SHR values. At present, it is not possible to explain the mechanism underlying this genetically de termined difference in response to diet.…”

“…It has been demonstrated in many differ ent studies that the type of dietary protein is a factor affecting plasma lipid levels in various experimental animals, and probably in man [1,2]. Therefore, the aim of the present study was to reveal possible cardiovascular conse quences of substituting soybean protein for casein in an atherogenic diet.…”

“…In previous studies with male spontaneously hypertensive an important role, the present studies using Sprague-Dawley rats were initiated. Besides exhibiting different blood pressure, SHR and Sprague-Dawley rats also show a quite differ ent plasma lipid response to an atherogenic diet [1].…”