The preferential mobilisation of C20 and C22 polyunsaturated fatty acids from the adipose tissue of the chick embryo : potential implications regarding the provision of essential fatty acids for neural development

The aim of this study was to determine the relative mobilisation of the different fatty acyl components of the triacylglycerol (TAG) of the chick embryo's adipose tissue in the light of the specific requirements of the developing neural tissues of the embryo for C20-22 polyunsaturated fatty acids. Pieces of adipose tissue, obtained from embryos at various developmental stages, were incubated in vitro in Dulbecco's Medium containing serum albumen. The fatty acid compositions of the initial tissue TAG and of the free fatty acid (FFA) mobilised from the tissue during 1 h of incubation were determined and compared. The composition of the FFA released into the medium under conditions of basal (i.e., unstimulated) lipolysis was markedly different in several respects from that of the TAG from which it originated. The polyunsaturated fatty acids, 20:4n-6, 20:5n-3, 22:5n-3 and 22:6n-3, were consistently found to be preferentially released into the medium, whereas the major fatty acyl constituents of the tissue, 16:0 and 18:1n-9, were selectively retained in the TAG. For example, at day 18 of development, the proportions (% w/w of fatty acids) of 20:5n-3 and 22:6n-3 released into the incubation medium were respectively 6.5 and 7.5 times higher than in the original tissue TAG. Glucagon stimulated the overall rate of mobilisation by approx. 2-fold and also partially suppressed the preferential mobilisation of C20-22 polyunsaturates. These results may be relevant to the elucidation of the means by which essential polyunsaturates are delivered from the yolk to the neural tissues of the embryo, with the implication of a mediatory role for the embryonic adipose tissue in this transfer.