O. M. Petterson

Effect of centrifugation at 20,000 x g on lipid distribution of human sera.

Summary The effects of centrifugation at 20,000 × g for 2 hours on lipid distribution of various human sera have been studied. In general, when neutral fat was below 176 mg%, very little, if any, cholesterol or phospholipids rose to the surface. When neutral fat content was markedly elevated, as much as 90% of both cholesterol and neutral fat and 50% of phospholipids underwent flotation. However, subjects with similar degrees of marked hyperlipemia appeared to separate into 2 major groups represented by moderate and marked degrees of flotation of neutral fat, the latter group being composed primarily of subjects with familial hyperlipemia. An inverse correlation was found between whole serum neutral fat content and percentage of total cholesterol remaining in the subnatant serum. Variations from these general patterns and possible clinical interpretations are being studied. We gratefully acknowledge a grant from the Richmond Area Heart Assn. in support of our work on lipid metabolism. Our thanks are due Dr. William Burton and Dr. Morton Bender as well as many practicing physicians in Richmond for collecting blood samples used in this study.

Fractionation of serum cholesterol.

Summary Chloroform extraction of normal serum, dried in vacuo from a frozen state, removed a relatively small but constant fraction of the total cholesterol. A very high percentage of the total cholesterol of the serum of nephrotic patients was extracted under the same conditions. The same was true of rabbits rendered hypercholesterolemic by the administration of cholesterol with their food. The readily extractable fraction was slightly elevated in all the hypothyroid cases studied and in some diabetic patients.

Effect of a Diet Deficient in Lipotropic Factors on the Lipoproteins of Rat Serum.

Summary The cholesterol and triglyceride content of the high- and low-density lipopro-teins of rats on a choline deficient diet for at least 3 weeks has been compared with that of controls on the same diet supplemented with choline. The deficient animals showed only about one-half the concentration of these lipids in the low-density lipoprotein fraction compared with the controls. Supplementation of the diet of the deficient animals with choline raised the concentration of these lipids to normal after a few days. The cholesterol content of the high-density lipopro-teins seemed not to be affected by the deficiency state. The triglyceride content, however, was depressed. We are indebted to Mr. E. W. Ruark, for phosphorus determinations.

Effect of hydrocortisone feeding on concentration of free fatty acids and other lipids of rabbit sera.

Summary Rabbits fed Purina rabbit chow supplemented with 30 mg of hydrocortisone/kg of diet showed a marked rise in FFA content of the serum as well as in serum cholesterol, phospholipids, and triglycerides. The addition of coconut oil at a 5% level to the diet augmented the effect. It is postulated that the various changes in serum lipid may be secondary to an increased mobilization of FFA from the adipose tissue as a result of the hydrocortisone feeding.

Plasma cholesterol of roosters under various conditions.

Summary Subcutaneous administration of diethylstilbestrol to cockerels caused a marked increase in the concentration of the “readily extractable” cholesterol of the plasma as well as in total cholesterol and neutral fat. Cholesterol feeding exerted a similar effect, but at moderately elevated plasma cholesterol levels the concentration of the “readily extractable” fraction was not as great as when the total cholesterol was raised by the administration of estrogenic substances. However, when the total cholesterol was high, about 700 mg %, practically all of it was present in the “readily extractable” form. Roosters receiving a high fat diet for several weeks usually showed a definite increase in the “readily extractable” fraction without a consistent increase in total cholesterol. When the diet contained 10% soybean lecithin; the concentrations of both the total cholesterol and of the “readily extractable” fraction dropped below those found in animals on the basal diet.

Effect of Lyophilization and Chloroform Extraction on Electrophoretic Migration of Serum Lipoproteins.

Summary Lyophilization of serum has been shown markedly to retard electrophoretic migration of some of the cholesterol normally associated with the beta-globulin area but to exert little effect on the cholesterol associated with the albumin + alpha1-globulins. The cholesterol which is extracted by cold chloroform from lyophilized serum comes primarily from that fraction normally found in the beta-globulin area or which remained around the starting point. It is suggested that the cholesterol thus removed represents primarily cholesterol which is associated with lipo- and chylomicrons.

Factors affecting extractability of cholesterol from lyophilized sera by cold chloroform.

Summary A study has been conducted on factors which affect the “readily extractable” cholesterol concentrations in serum. The results showed that (a) in general, REC values increased as triglyceride and cholesterol contents of the serum and chylomicra increased, but a notable exception was high REC values in nephrotic subjects in whom chylomicron contents of cholesterol and triglyceride were low, (b) addition of the sodium salts of long chain fatty acids to serum prior to lyophilization markedly increased cholesterol extractability, (c) addition of crystalline human serum albumin to sera with high REC concentrations markedly reduced REC values; the albumin also reduced REC concentration in most normal sera but in no case did it completely disappear, (d) traces of moisture in the chloroform used for the extraction had little or no effect on most sera with low REC concentration but markedly increased it in sera with high REC concentration. It is suggested that the concentration of non-albumin bound free fatty acids may play a major role in regulating REC concentrations in various sera.

Serum lipids in hypercholesterolemic rabbits.

Summary Intravenous injections of the surface active agent Triton WR1339 into rabbits caused a marked increase in serum neutral fat as well as in cholesterol and phospholipids. A large percentage of this increase was found in the lipid fraction which rose to the surface when serum was centrifuged at 20,000 g for 2 hours or more. Administration of Triton to rabbits rendered hypercholesterole-mic by cholesterol feeding decreased the percentage and absolute value of total cholesterol remaining in the subnatant fraction after highspeed centrifugation. After several injections, concentration of cholesterol in the subnatant dropped well below the pre-injection value in spite of increase in total serum cholesterol concentration. It is suggested that an increase in percentage of the cholesterol associated with chylomicrons together with a probable decrease in the fraction associated with lipomicrons might be factors in Triton-induced inhibition of development of atherosclerosis in cholesterol-fed rabbits.

Effect of High Speed Centrifugation on Distribution of Serum Cholesterol

Summary As a general rule a fairly large percentage of total serum cholesterol rose to the surface when sera containing markedly elevated amounts of “readily extractable cholesterol” were centrifuged at 20.000 g for 2 hours. Sera having a normal “readily extractable cholesterol” concentration showed very little of the cholesterol rising to the surface under the same conditions. A few subjects, including most nephrotic patients studied, differed markedly from this pattern. In these cases, only a small amount of cholesterol rose to the surface during centrifugation in spite of the fact that the sera had markedly elevated “readily extractable cholesterol” concentrations. It is suggested that the cholesterol which rose to the surface is cholesterol which is associated with chylomicrons, while that which did not rise but which is a part of the “readily extractable cholesterol” is cholesterol present in lipomicrons.

Effect of Intravenous Administration of Paritol-C∗ on Serum Lipids of Hypercholesterolemic Rabbits.†

Summary The intravenous injection of Paritol-C into hypercholesterolemic rabbits has been shown to cause a marked drop in the “readily extractable” cholesterol fraction, as well as in total cholesterol.