Experimental atherosclerosis and cardiac infarcts in rats

The rat as an experimental animal

The development and characterization of many inbred, congenic, and recombinant strains of rats in recent years has led to the detailed genetic description of this species, especially in regard to its major histocompatibility complex. This information has contributed substantially to the study of comparative genetics and has greatly enhanced the utility of the rat in a variety of areas of biomedical research. This article focuses on the use of the rat in immunogenetics, transplantation, cancer-risk assessment, cardiovascular diseases, and behavior.

The effect of lowered environmental temperature on lipid metabolism in rats fed on normal and high-fat, high-cholesterol diets

1. Prolonged intermittent exposure to reduced environmental temperature (+2°) produced in rats given a nutritionally well-balanced diet a decrease in the concentration of esterified fatty acids in the blood serum, liver and epididymal fat tissue. In the last there was a significant increase in the unesterified: esterified fatty acid ratio. The hepatic synthesis of fatty acids from [1–14C]acetate remained unchanged. A decrease in the concentration of cholesterol was found in the blood serum, liver and lungs of animals exposed to cold.

2. When a high-fat, high-cholesterol diet was given, exposure to cold increased the mobilization of lipids; this was indicated by the elevation of the unesterified fatty acid levels in the blood serum and in the epididymal fat tissue. In rats given the high-fat diet the lipotropic action of cold on the liver was confirmed. This action was characterized by a decrease of esterified fatty acid levels and by an increase of glycogen concentration in the liver. This effect is probably due to a lowering of hepatic lipogenesis and to increased oxidation of fatty acids in the liver tissue. In rats given the high-fat dict, cold exposure produced an increased cholesterol accumulation in the tissues and more pronounced morphological changes in the myocardium.

Thrombosis in Connection with Serum Lipidic Changes in the Rat

Addition of either propylthiouracil or cholic acid to a natural diet (Purina Laboratory Chow) enriched in certain lipids resulted in hypercholesteremia and hyperlipemia of about the same amplitude. However, only cholic acid could induce a high incidence of thrombosis and cardiac infarct and a regular decrease in the percentage of serum alphalipoproteins with an electrophoretic pattern similar to that found in essential hyperlipemia or in certain nephrotic syndromes associated with thrombosis. In the rat, the thrombi, located in the arterioles and the capillaries of the heart and other organs, presented a histological picture that resembled thrombotic-thrombocytopenic-purpura rather than coronary disease. This thrombotic phenomenon was preceded by an acute increase in serum cholesterol and total lipids and was accompanied by the production of a large quantity of macrophages, with a foamy appearance, in the lung and the spleen. If propylthiouracil was added to this thrombogenic diet, the survival time of the animals was considerably shortened and the percentage of iufarcts reduced, but in this case, thrombosis was mainly located in the ventricles and the aorta. Under these experimental conditions, both of the hypercholesterolemic agents being used, lipidic infiltration of the vessels was detected but no tissular reaction that could result in atheromatous plaques.

Coronary atherosclerosis in rats exposed to cold

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Further Studies on Experimental Atherosclerosis and Dietary Pyrimidines: Orotic Acid, Thiouracil, and Uracil in Male and Female Rats

The comparative potencies of uracil nnd thiouracil in terms of thyroidal changes, hypercholesteremia, azotemia, and incipient atherosclerosis were determined in rats fed cholesterol and cholic acid. Higher dietary levels of uracil were required to produce changes similar to those seen with thiouracil. Certain dietary components related to uracil were also studied. Orotic acid was found to have a dramatic effect on female rats: it favored a markedly lower serum cholesterol level and less cardiovascular sudanophilia. When orotic acid was combined with uracil, the uracil-induced hypercholesteremia and atherogenesis were significantly inhibited, particularly in the females. Orotic acid also protected against the uracil-induced thyroid hyperplasia in these females.