472 V. BLOOD LIPIDS 



ciently in the liver than do the chicken or the rabbit accounts for the varia- 

 tion in blood cholesterol noted in the several species. 



The relationship between dietary cholesterol and blood cholesterol in 

 the rabbit has recently been investigated from an entirely new viewpoint 

 by Gofnian and his co-workers. 96,98 These investigators found that the 

 plasma of normal rabbits contains a lipoprotein, having a hydrated density 

 of 1.03, which contains about 30% of cholesterol by weight. When serum 

 from normal rabbits was subjected to ultracentrifugation, the lipoprotein 

 appeared with a flotation value of 5-8 (S f = 5-8) . 



When cholesterol was fed to rabbits in dosages of 3 g. per week, an inter- 

 esting sequence of events ensued. At first there was an increased concen- 

 tration of the S/ 5-8 fraction amounting to as much as four times the 

 previous values. However, after a longer period (thirty to forty days) 

 another series of molecules appeared which had flotation rates varying 

 between S f 10 and 30. The S f 10-30 class components, also, do not usually 

 appear until the serum cholesterol exceeds 200-250 milligram per cent. 96 

 In some instances, components having a higher S f value are likewise formed. 

 Subsequent to the appearance of the Sf 10-30 class, the Sf 5-8 molecules 

 are maintained at approximately the same level, while the S f 10-30 class 

 continues to increase. Variations obtain between different rabbits in the 

 amount of these components, which range from none at all to any number 

 of the higher S f components. A comparison of the proportionate amounts 

 of S f 5-8 and S f 10-30 in the blood of rabbits, after fifteen weeks of chole- 

 sterol feeding, with the extent of atherosclerosis, is shown in Figure 5. A 

 further discussion of the flotation rates of cholesterol compounds is given 

 in the next section, dealing with investigations on man. 



(b) Arteriosclerosis in Man. a'. Comparison of Atherosclerosis in 

 Rabbits and Arteriosclerosis in Man: Although a hypercholesterolemia 

 following cholesterol feeding is associated with the production of an 

 atherosclerosis in rabbits, there is some question as to whether or not 

 these experimental data apply to arteriosclerosis in man. Although 

 Leary 757 reported that the lesions obtained from the blood vessels of rabbits 

 having an experimentally produced atherosclerosis and those obtained 

 from the coronary arteries of atherosclerotic human patients on autopsy 

 were similar, their distribution is not confined to such a limited area in the 

 rabbit as in man 718 ; in fact, atheromatous lesions have been demonstrated 

 not only in the aortic and systemic vessels of rabbits but also in the pul- 

 monary system 719 and even in the veins. 720 According to Peters and Van 

 Slyke, 202 the experimental atherosclerosis of rabbits differs from the disease 



767 T. Leary, Arch. Pathol, 17, 453-492 (1934). 



