376 V. BLOOD LIPIDS 



Green, and Page 176 reported that the lipoproteins in the sera of the normal 

 chicken, rat, rabbit, opossum, monkey, man, cat, and dog had flotation 

 rates from Sf 1 to Sf 15. While no lipoproteins were present in the sera of 

 the cat and dog with a rate faster than 23, lipoproteins with rates as high as 

 30 occurred in the sera of the rat, the opossum, the sheep, the monkey, and 

 of some human subjects. The lipoproteins of the class having rates of 

 25 or greater are characteristic in the case of guinea pigs, chickens, rabbits, 

 and of some monkey and human sera. Fasoli and co-workers 177 reported 

 that the serum of the dog is richer in high-mobility lipoproteins migrating 

 with albumin, and in on-globulin, than is human serum. 



Species variations exist not only in the type of lipoproteins but also in 

 the absolute amounts present. In the S f 1-15 class, the following amounts 

 (milligram per cent) of lipoproteins were found 176 : cat, dog, opossum, 

 and monkey, > 200; man, 150; rabbit, 100; and sheep, 40. In the case 

 of the S f 15-40 class, the following values (milligram per cent) were re- 

 ported 176 : rat, 12; rabbit, sheep, opossum, cat, and dog, 50; and man 

 and monkey, > 200. 



The proportion of lipoproteins is altered by certain other physiological 

 and pathological conditions. Thus, age appears to be a factor. Forbes 

 et al. m found that a large proportion of the cholesterol of lyophilized serum 

 of old hens is "readily extractable," in contradistinction to the low pro- 

 portion in this fraction of the serum of roosters and young chickens. In 

 the case of the old hens, the proportion of "readily extractable" cholesterol 

 shows a correlation with the neutral fat content. When cholesterol 

 is fed to rabbits over a long period, the hypercholesterolemia is accom- 

 panied by a hyperglobulinemia ; Fishberg et al. m have shown that this 

 consists of i3-globulin. The high level of lipoprotein obtained thirty hours 

 after irradiation is directly correlated with the subsequent death of the 

 animal. 180 It is suggested that x-irradiation brings about a conversion of 

 low-density lipoprotein to higher density components. The injection of 

 heparin following irradiation hastens the return of lipoprotein levels to 

 normal. Hewitt et al. m also demonstrated that the injection of toluidine 



176 L. A. Lewis, A. A. Green, and I. H. Page, Am. J. Physiol., 171, 391-400 (1952). 

 » 77 A. Fasoli, E. B. Magid, M. D. Glassman, and P. P. Foa, XIX Intern. Physiol. 

 Congress, Montreal Abst. (Aug.-Sept,, 1953), 340-341. 



178 J. C. Forbes, G. H. L. Dillard, W. B. Porter, and O. Petterson, Proc. Soc. ExpU. 

 Biol. Med., 71, 26-28(1949). 



179 A. M. Fishberg, L. Friedfeld, I. Hoffman, E. R. Slotter, and E. H. Fishberg, Proc. 

 Soc. Exptl. Biol. Med., 75, 301-303 (1950). 



180 J. E. Hewitt, T. L., Hayes, J. W. Gofman, H. B. Jones, and F. T. Pierce, Am. J. 

 Physiol, 172, 579-587 (1953). 



