Lipid metabolism in the normal and vitamin B12-deficient chick embryo

Abstract

The lipids of normal and vitamin B12-deficient chick-embryo livers, extrahepatic tissues and yolk sacs after 15, 17 and 19 days of incubation have been examined by fractiona-tion on columns of silicic acid. In the normal embryos, the total lipid content of the livers increased during the last week of development and the greater part of this increase could be accounted for by the increase in esterified sterol, which accounted for 70% of the liver lipid in the 19-day-old embryos. During the 17-19 days period of development the total lipid content of the extrahepatic tissues also increased but this increase was mainly due to the triglyceride fraction. The only appreciable change in the composition of the yolk-sac lipids during the period of development under study was an increase in the ratio cholesterol ester total cholesterol. Although there was no difference in the total lipid content of the vitamin B12-deficient and normal embryo livers, vitamin B12 deficiency did result in a pronounced decrease in the sterol ester and a pronounced increase in the triglyceride content at each stage of development. At 15 days the phospholipid content of the deficient embryo livers was higher and at 17 days the free sterol content was lower than in the corresponding normal embryo livers. The lipids of the extrahepatic tissues and yolk sacs were not affected by a deficiency of vitamin B12. The differences in composition of the liver lipids are interpreted as being due mainly to a decreased utilization of triglyceride by the vitamin B12-deficient chick embryo. The mechanism of the effect of vitamin B12 deficiency on the lipid metabolism of the chick embryo is discussed.