436 V. BLOOD LIPIDS 



is now known that the metabolism of cholesterol and that of the essential 

 fatty acids are closely interrelated. 



It was first demonstrated by Alfin-Slater and her collaborators 363 that 

 the presence of essential fatty acids is required to aid in the regulation of 

 the cholesterol in the blood and tissues. The variations in the plasma 

 cholesterol level as affected by diet are shown in Table 14 (page 435). 



It would thus appear that, although diets low in fats cause a decrease in 

 the level of plasma cholesterol, they also result in a concomitant increase 

 in the cholesterol deposited in the liver, adrenal glands, and possibly other 

 organs. It is not known whether or not this results from the inability of 

 cholesterol to be transported from the liver when the supply of linoloate 

 is deficient, or whether the essential fatty acids are required in the catabo- 

 lism of cholesterol. Bromer and Day 496 have reported that the increase in 

 liver cholesterol was greater after cholesterol was fed to rats on an essential 

 fatty acid-free diet than when it was given to animals on a normal diet; 

 moreover, a greater hypercholesterolemia obtained, under these conditions, 

 in the rats on the fat-free regimen than in the normal controls. Methyl 

 linoleate was shown to lower the cholesterol level in both the blood and the 

 liver. 



f. The Blood Lipids as Affected by Disturbances of the Endocrine 

 Glands. The most potent factors which influence the metabolism of the 

 lipids are the secretions of the endocrine glands. Of these hormones, 

 those produced by the thyroid gland and by the islet tissue of the pancreas 

 share the limelight as the most important in relation to the blood lipids. 

 However, the pituitary gland (both the anterior and the posterior portions), 

 the adrenal cortex, and the sex glands also have an influence on the utiliza- 

 tion of several of the lipids. Although one finds alterations in lipid distri- 

 bution when abnormalities of one gland become prominent, the resultant 

 effects must, in most cases, be due to simultaneous variations in function of 

 several of the endocrine glands. Workers in the field of endocrinology 

 have come to realize that the activity of any one endocrine gland cannot 

 be segregated, but practically always results in a variation in behavior of 

 one or more of the other members of the group. 



(a) Variations Primarily Related to the Thyroid Gland. Practically 

 all experimental and clinical evidence has indicated the very marked control 

 exerted by the thyroid gland on the several blood lipids. When the secre- 

 tion of the thyroid hormone is excessive, as occurs in exophthalmic goiter 

 or other types of hyperthyroidism, a marked decrease in all blood lipids 



496 w # W. Bromer and H. G. Day, Proc. Am. Chem. Soc, Paper No. 140, Chicago, 

 Sept., 1953. 



