402 V. BLOOD LIPIDS 



liver glycogen during the twenty-four hour period, 276-278 it has been shown 

 that these variations were related to the feeding habits of the animals. 276-278 

 When rats were fed constant amounts of carbohydrate at spaced intervals 

 throughout the day and night, and the animals were sacrificed twelve hours 

 later, no evidence of a diurnal cycle in carbohydrate storage obtained. 278 



Although there is considerable evidence of marked variations in blood 

 lipids after the ingestion of heavy doses of fats, Boyd 260 could find no signifi- 

 cant variations of total lipid in human subjects given normal diets with 

 moderate amounts of fat. Samples were collected at intervals of three or 

 four hours throughout the twenty-four-hour period. The variations be- 

 tween the different subjects were two or three times as great as were any 

 diurnal changes. 



Cholesterol appears to remain quite constant in the blood throughout the 

 twenty-four-hour period. Although McEachern and Gilmour 279 noted 

 wide variations in the blood cholesterol values of twenty-eight subjects 

 over five-hour intervals, more recent results have supported the viewpoint 

 that alterations in this lipid fraction are insignificant and inconstant during 

 the course of the day. 260,280 The blood level of cholesterol remains largely 

 unaffected by ordinary meals and by the usual activities. 281,282 



e. The Effect of Menstruation. With the development in our knowledge 

 concerning the hormones which control the female sex cycle, more exact 

 information has become available on the relationship of this function to 

 lipid metabolism. Two hormones are now known to be secreted by the 

 ovaries, namely, estrone, which occurs in the follicles, and progesterone, 

 which is a product of the corpus luteum. 



Okey and Boyden 283 reported that a decrease in blood cholesterol occurred 

 in women during or within a few days of the onset of the menstrual period ; 

 this was followed by an increased level in blood cholesterol. No similar 

 changes could be consistently demonstrated in the level of fatty acids and 

 phospholipids in the serum. Even more marked changes in the cholesterol 

 level were noted by Kaufmann and Muhlbock, 284 who found a decrease in 

 serum cholesterol as great as 40% at the menstrual period. The fact that 



276 G. M. Higgins, J. Berkson, and E. Flock, Am. J. Physiol, 102, 673-682 (1932). 



277 G. M. Higgins, J. Berkson, and E. Flock, Am. J. Physiol, 105, 177-186 (1933). 



278 H. J. Deuel, Jr., J. S. Butts, L. F. Hallman, S. Murray, and H. Blunden, J. Biol 

 Chem., 123, 257-265 (1938). 



279 J. M. McEachern and C. R. Gilmour, Can. Med. Assoc. J., 26, 30-33 (1932). 



280 C. W. McClure and M. E. Huntsinger, /. Biol. Chem., 76, 1-18 (1928). 



281 M. Bruger and I. Somach, J. Biol. Chem., 97, 23-30 (1932). 



282 K. B. Turner and A. Steiner, J. Clin. Invest., 18, 45-49 (1939). 



283 R. Okey and R. E. Boyden, J. Biol. Chem., 72, 261-281 (1927). 



284 C. Kaufmann and O. Muhlbock, Arch. Gynakol, 136, 478-502 (1929). 



