The Accumulation of Serum Cholate and its Relationship to Hypercholesteremia

SERUM BILE ACID LEVELS IN HYPERCHOLESTEROLAEMIC PATIENTS

A shortened method of estimating serum bile acids is described, based on extraction and the measurement of fluorescence in sulphuric acid solution at 37 degrees C. The cholate and dihydroxy bile acid fractions are determined separately by measurements made one hour and 24 hours after preparing the solution. About 1% of the serum cholesterol escapes separation and appears in the sulphuric acid solution; in its fluorescent properties it behaves in a manner almost identical with dihydroxy bile acids. As a result, the normal serum bile acids are overestimated by about 2 mg./100 ml. This effect is unimportant in cases of jaundice. In non-jaundiced cases with hypercholesterolaemia, the apparently raised serum bile acid levels are accounted for by the interference from cholesterol and there is no evidence that a raised serum cholesterol level is usually associated with raised serum bile acids.

Thrombin binding to platelets from hypercholesterolaemic rats

Platelets from rats made hypercholesterolaemic with a diet enriched with milk fat and cholesterol and containing taurocholate to promote hypercholesterolaemia aggregated more extensively to a low concentration of thrombin than platelets from rats given a milk fat-enriched diet containing sitosterol. Total and specific binding of thrombin to platelets from hypercholesterolaemic rats was significantly greater than in controls when expressed per mg platelet protein, per mumol platelet cholesterol, or per unit relative surface area. Total and specific binding of thrombin per platelet were not different between the groups. However, platelets from hypercholesterolaemic rats had less protein and cholesterol, were smaller and had less surface area than control platelets; platelet cholesterol content expressed per mg platelet protein was not different. Thus, the increase in thrombin-binding to the smaller platelets from hypercholesterolaemic rats during the first 10 s after its addition may be responsible, at least in part, for the hypersensitivity of these platelets to thrombin.

The effect of dietary saturated fat and cholesterol on platelet function, platelet survival and response to continuous aortic injury in rats

Induction of hypercholesterolemia in rats by diets containing milk fat, cholesterol and taurocholate caused increased sensitivity of platelets to thrombin-induced aggregation and release, but not to ADP- or collagen-induced aggregation or release. This hypersensitivity to thrombin persisted in the presence of CP/CPK to convert released ADP to ATP, and aspirin to block formation of thromboxane A2. The increased sensitivity of platelets to thrombin in hypercholesterolemic animals was associated with an increase in 18:1 omega 9, 18:2 omega 6 and 20:3 omega 6 and a decrease in 20:4 omega 6 and 22:4 omega 6 in their phospholipids. Hypercholesterolemic animals also had a shortened platelet survival that did not appear to be due to an alteration in the lipid composition of the platelets. The diet-induced changes in platelet function were not associated with enhanced thrombosis in animals with indwelling aortic catheters, but were associated with increased platelet accumulation on the exposed subendothelium.

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.

The mechanism responsible for the hypercholesteremia induced by triton WR-1339

Injection of triton WR-1339 into rats leads to a rapid increase in the cholesterol, cholate, and various lipid fractions of their blood. The increase in cholesterol is confined to the blood itself. The cholesteremic effect of triton was not dependent upon a prior accumulation of cholate in plasma. The liver was found to be the source of the excess cholesterol but the rate of cholesterol synthesis, the excretion of cholate, and the cholesterol content of the liver were not changed by injection of triton. The cholesteremic effect of triton is not due to alteration in the intestinal excretion of cholesterol. Transfer of blood between "tritonized" and normal rats leads to a disappearance of the hypercholesteremia in the former and its appearance in the latter animals. The plasma proteins of rats injected with triton are markedly changed qualitatively. Heparin was found to inhibit the hypercholesteremic effect of triton. The hypercholesteremia following triton injection appears to be due to a fundamental physicochemical change in the plasma proteins produced by injection of this detergent.

Induced hypercholesterolemia and atherogenesis

An attempt has been made to elicit atherosclerosis in rats by duplicating as far as possible those conditions which in other animals are atherogenic. By making the rats hypothyroid and feeding cholic acid and cholesterol, severe hypercholesterolemia and abnormal beta-lipoproteins appeared along with heavy lipid infiltration of the kidneys, liver, heart and aorta. Aortic and coronary atherosclerosis might have been expected in rats exposed to so much atherogenic material in the blood, but it was not found. Despite lipid infiltration in the intima of the vessels, no appreciable tissue reaction to it occurred; we believe the lack of tissue response is one of the chief causes for the failure of atherosclerosis to develop. Thus tissue response and receptivity to lipid deposition seem to be important mechanisms in atherogenesis.