Estrogen in the Chick Embryo Plays a Role in Utilization of Plasma Lipids during Incubation.

An aromatase inhibitor, Fadrozole (CGS16949A), was administered into chick embryo on the 5th day of incubation to clarify the roles of endogenous estrogen in the regulation of circulating lipoprotein levels during the development. The plasma of 10-, 16- and 20-day embryos and neonatal chicks were separated by polyacrylamide gel electrophoresis. Amounts of plasma lipoproteins, high density lipoprotein (HDL), low density lipoprotein (LDL) and very low density lipoprotein (VLDL) were then measured using a densitometer and expressed as a percentage in total lipoproteins. Changes in HDL percentages of the groups treated with the aromatase inhibitor (AI group) and propylene glycol (Vehicle group) showed similar patterns during the experimental period. This was also the case in the changes in LDL percentages. The 16-day embryos of the AI group, in which endogenous estrogen synthesis was inhibited, showed a distinctly high VLDL percentage, whereas plasma VLDL in the Vehicle group showed only a little developmental changes. The plasma concentration of triglyceride (a major component of VLDL), phospholipid and total cholesterol in the AI group showed a profile similar to that of VLDL, with the maximum level in the 16-day embryo. These results suggest that endogenous estrogen of the embryo plays an important role in the utilization and resulting clearance of plasma lipids from the circulation, in addition to its well-documented role in sex differentiation.