RESUMO
The effects of differences in the fatty acid composition of the lipids of egg yolk on the subsequent levels of arachidonic acid (20:4n-6) and docosahexaenoic acid (22:6n-3) in the total phospholipids and in the isolated phospholipid classes of the embryonic brain were investigated by a comparison of two domesticated avain species, the chicken and the duck. The yolk phospholipids of chicken eggs contained similar proportions of 20:4n-6 and 22:6n-3 (approx. 6% wt/wt of total fatty acids). In marked contrast, the yolk phospholipids of commercially produced duck eggs contained an overwhelming preponderance of 20:4n-6 over 22:6n-3 (approx. 10% cf.1%). These differences between the yolks of the two species were only partly reflected in the fatty acid compositions of the total phospholipids of the embryonic brains at equivalent developmental stages. Typically, the chicken brain phospholipids contained approximate proportions of 20:4n-6 and 22:6n-3 of 8% and 17%, respectively, whereas both these polyunsaturates were present at approx. 11% in the duck samples. The brain phospholipids were resolved into their component phospholipid classes by high performance liquid chromatography. In both species, phosphatidylcholine contained only low levels of 20:4n-6 and 22:6n-3, whereas phosphatidylethanolamine displayed a high content of 22:6n-3. Phosphatidylserine was also rich in 22:6n-3 whereas phosphatidylinositol exhibited a high proportion of 20:4n-6. The results suggest that the relatively low level of 22:6n-3 in the yolk of duck eggs is partly compensated for by an enhanced efficiency in the incorporation of this fatty acid into the brain phospholipids, in comparison with the chicken.