FACTORS ALTERING CONCENTRATION OF BLOOD LIPIDS 429 



hyperlipemia is by dissolution of the chylomicrons. The injection of 

 heparin greatly accelerates the passage of the neutral fat in the chylo- 

 microns through the capillary walls to the tissues, where its metabolism 

 is facilitated. This transport mechanism is absent from the brain; this 

 organ uses only insignificant amounts of fat in its metabolism. According 

 to Swank, 453 the tendency of the chylomicrons to form clusters is increased 

 after a fat meal; this tendency is slight in whole blood without heparin, 

 as well as in oxalated or citrated blood, but it is marked in heparinized 

 blood. The tendency toward clustering also varies with different indi- 

 viduals 453,454 ; it is less after the feeding of unsaturated fats than after the 

 administration of saturated fats. Pregnancy and high-fat diets increase 

 this property, while it is reduced when a low-fat diet is taken, Zinn and 

 co-workers 455 reported that heparin and a related product, "treburon," 

 were both equally effective in reducing lipomicronemia within thirty to 

 sixty minutes. In addition to its effect on neutral fat in the chylomicrons, 

 Basu and Stewart 456 reported that the injection of heparin reduces both 

 free and esterified cholesterol in the plasma. 



Grahm and co-workers 457 were the first to demonstrate that heparin may 

 have an important part in the regulation of the size of the lipoprotein 

 molecule elaborated in the plasma. When heparin was given to rabbits 

 or to human subjects, a considerable reorientation of the low density 

 S f 3-8 lipoproteins occurred. However, the most important reaction was 

 the retardation in the formation of the Sf 10-50 lipoproteins which would 

 normally occur during cholesterol feeding. Boyle, Bragdon, and Brown, 458 

 by the use of ultracentrifugation and by chemical means, also demonstrated 

 that heparin causes an increase in the high-density ai-lipoproteins at the 

 expense of certain low-density lipoproteins. Such changes were shown to 

 occur in vitro in plasma obtained after the injection of heparin. They 

 suggest that an enzymatic conversion of one lipoprotein class to another 

 results from the injection of heparin. Milch alone 459 and with co-workers 460 



453 R. L. Swank, Am. J. Physiol, 164, 798-811 (1951). 



454 W. J. Messinger and Y. Porosowska, Proc. Soc. Exptl. Biol. Med., 82, 164-167 

 (1953). 



455 W. J. Zinn, J. B. Field, and G. C. Griffith, Proc. Soc. Exptl. Biol. Med., 80, 276-278 

 (1952). 



466 D. P. Basu and C. P. Stewart, Edinburgh Med. J., 57, 596-599 (1950). 



457 D. M. Graham, T. P. Lyon, J. W. Gofman, H. B. Jones, A. Yankley, and J. Simon- 

 ton, Circulation, 4, 465 (1951). 



468 E. Boyle, J. H. Bragdon, and R. K. Brown, Proc. Soc. Exptl. Biol. Med., 81, 475- 

 477(1952). 



459 L. J. Milch, Federation Proc, 12, 351 (1953). 



460 L. J. Milch, R. F. Redmond, W. W. Calhoun, and H. I. Chinn, Am. J. Physiol, 

 170, 346-350 (1952). 



