Embryonic development of mevalonate metabolism by sterol and nonsterol pathways in chick brain and liver.

The embryonic development of the sterol and nonsterol mevalonate metabolism has been investigated in chick brain and liver. The shunt pathway of mevalonate was negligible in both tissues throughout 10-21 days of embryo development. Mevalonate incorporation into nonsaponifiable lipids was higher in liver than in brain. A pronounced peak was found in liver at 12 days of incubation, while only small differences were observed in brain. Lanosterol and cholesterol were the major sterols synthesized in brain, followed by desmosterol and squalene. Their relative percentages did not change significantly during 10-16 days and slightly decreased thereafter. In liver, cholesterol and squalene were the major sterols observed during the first days of incubation with a developmental pattern similar to that found in the mevalonate incorporation into nonsaponifiable lipids, while relative percentage of squalene oxides sharply increased between 12 and 16 days of embryonic development. The importance of cholesterol esters accumulation in the inhibition of cholesterogenic activity is discussed.