Abstract
In the course of an investigation of cholesterol metabolism in the rat, a survey of the literature indicated a paucity of knowledge concerning the normal fluctuations of blood cholesterol in this species. The present communication deals with such values in normal adult albino rats of both sexes. Inasmuch as there is a large residue of free cholesterol in the erythrocytes, a circumstance essentially vitiating the determinations on whole blood, the necessity of using plasma or serum should be emphasized.
The rats used in this study were breeding stock and were of the Osborne and Mendel strain obtained from the Connecticut Agricultural Experiment Station. The females were not used until one month or more had elapsed after weaning of litters. All animals were fed a stock diet which includes a mixture of 97% G.L.F. calf meal 1 and 3% cod liver oil. During the lactation period the females received in addition, a paste food consisting of whole milk powder 25%, casein 25%, wheat germ 20%, and lard 30%. The food was removed approximately 15 hours before killing the animals.
Under ether anesthesia, the blood was drawn from the abdominal aorta into oxalated centrifuge tubes. All blood samples were secured within 5 minutes after the animal was anesthetized. Promptness in obtaining blood samples is necessary as is emphasized by the results of Mahler 2 who showed a definite rise in blood cholesterol, after 5 to 7 minutes, proportional to the duration of the anesthesia. With few exceptions 4 cc. or more of plasma were obtained from each animal; the plasma of 2 rats was combined in cases where it was impossible to obtain a volume of 4 cc. from an individual animal. The plasma was extracted with alcoholether (3:1) mixture and the precipitated protein washed with portions of boiling ethyl ether to insure complete extraction of the cholesterol.
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