Unsaturated fatty acid compositional changes and desaturation during the embryonic development of the chicken (Gallus...

An investigation has been made to correlate the activities of the delta 9- and delta 6-long chain fatty acid desaturation systems with the increased levels of oleic and arachidonic acids in the liver relative to the yolk sac membrane of the chick embryo during the last week of development. The membrane exhibited high levels of both stearic and linoleic acid desaturation in the early stages of yolk lipid mobilization, the activities of both enzyme systems decreasing with the approach of hatching. Stearic acid desaturation in the liver also decreased with the approach of hatching, but linoleic acid desaturation increased. The observed levels of desaturation in the yolk sac membrane are capable of making a considerable contribution to the accumulations of mono- and polyunsaturated fatty acids in the embryonic liver, the requirement for which does not appear to be satisfied by the yolk lipids. With the approach of hatching and the functional regression of the yolk sac membrane, the role is taken over by the embryonic tissues.