SITE OF SYNTHESIS OF PLASMA LIPIDS 



393 



In a later study which lasted over two years, Bloor 227 followed the blood 

 lipids at frequent intervals in the case of two dogs which were fed a fat-low 

 diet; the food intake was adjusted to maintain a constant body weight. 

 The average value of total lipids found in the first dog was 337 ± 41 

 milligram per cent (112 samples), with a range of 256 to 412 mg., while the 

 mean in the second animal was 472 ± 40 milligram per cent (80 analyses), 

 with a range of 390 to 572 mg. The average standard deviations amounted 

 to 13 and 9%, respectively. The results on phospholipids and cholesterol 

 are given in the table below. 



Test animal Phospholipid Cholesterol 



Dogl 



Grand average (mg. %) 169 ± 22 80 ± 14 



Range (mg. %) 137-208 00-109 



Average standard deviation (%) 13% 17% 



Dog 2 



Grand average (mg. %) 234 =fc 27 133 ± 14 



Range (mg. %) 198-300 110-155 



Average standard deviation (%) 11% 11% 



5. The Site of Synthesis of Plasma Lipids 



It is virtually certain that practically no synthesis of lipids occurs in the 

 blood itself. The cholesterol and phospholipids present in the blood in 

 periods other than during digestion are presumably maintained at a con- 

 stant level by means of supplies of these components furnished by the liver. 

 It is generally believed that the neutral fat present in the plasma may orig- 

 inate from the gastrointestinal tract, the liver, or from the fat depots, 

 depending upon the state of alimentation. 



The experimental data on the origin of plasma phospholipids leave little 

 doubt that they are largely if not entirely synthesized in the liver. Al- 

 though Fishier and co-workers 228 demonstrated substantially the same 

 amount of phospholipid synthesis in the kidney and small intestine of hepa- 

 tectomized dogs as of normal animals, after the injection of P 32 , yet only 

 negligible amounts of newly synthesized phospholipid appeared in the 

 plasma when the liver was absent. Thus, it was concluded that, although 

 the small intestine and kidney can synthesize phospholipids, only the liver 

 can serve as the source of the plasma phospholipids. Ramney et al. 229 



227 W. R. Bloor, /. Biol. Chem., 103, 699-705 (1933). 



228 M. C. Fishier, C. Entenman, M. L. Montgomery, and I. L. Chaikoff, /. Biol. Chem., 

 150, 47-55 (1943). 



229 R. E. Ramney, I. L. Chaikoff, and C. Entenman, Am. J. Physiol, 165, 596-599 

 (1951). 



