The fatty acid composition of the main phospholipid fractions of the rumen and abomasum tissues of foetal and adult sheep.

Abstract

AbstractThe fatty acid composition has been determined on phosphatidyl choline, phos‐phatidyl ethanolamine and sphingomyelin fractions earlier isolated from the rumen and abomasum tissues of foetal and of adult Romney sheep.The major proportion of polyunsaturated fatty acids was found in the phosphatidyl ethanolamine (17 to 43%) fraction and this was reduced in the phosphatidyl choline (7 to 25%) and sphingomyelin (1 to 4%) fractions. These features are in keeping with the results for mammalian tissues generally. The phosphatidyl ethanolamine fractions were further characterised by the low content of palmitic acid (<8%) compared with 25 to 30 % in the phosphatidyl choline fractions and 29 to 52% in the sphingomyelin fractions and by the occurrence of cyclopropane fatty acids. Consistent with the findings of other workers on mammalian tissues, the sphingomyelin fractions contained a relatively high content (16 to 27%) of higher w‐saturated fatty acids including 22:0,23:0,24:0 and 25:0 and of tetracos‐14‐enoic (24:1 ω9) acid (5 to 16%). The total amounts of acids above C20 tended to vary inversely with the levels of palmitic acid whereas the levels of stearic acid were relatively constant at 13 to 17%.Changes in fatty acid composition with age were generally not marked but the tissues of the foetus were distinguished from those of the foetus were distinguished from those of the adult by their substantial amount of eicosa‐5,8,11‐trienoic (20:3 ω9) acid together with relatively low contents of linoleic (18:2 ω6) and linolenic (18:3 ω3) acids and to a leser extent by reduced level of acids of the ω3 series. This was particularly reflected by the ratios of ω6/ω3 C20 + C22 acids in the phosphatidyl ethanolamine fractions, the valucs for the foetal rumen and abomasum tissues being 1.03 and 1.07, respectively, compared with corresponding values of 0.78 and 0.72 found in adult sheep.The results are consistent with a requirement for C20 and C22 polyunsaturated acids of the ω3 and ω6 series and some penetration of maternal fatty acids through the placenta. The resemblance between the fatty acid make‐up and composition of foetal and maternal phospholipids suggests the possibiligy of transference of intact or lyso‐phospholipids from the mother to the foetus through the placenta. However, such a possibility is counter‐indicated by consideration of previous work using labelled intermediates and by the mechanism of conversion of linoleic and linolenic acids requiring their CoA derivatives in the formation of the corresponding polyunsaturated C20 + C22 acids. Nevertheless, the sharp cut‐off of exogenous maternal fatty acids from the foetal triglycerides and their inclusion in the foetal phospholipids are not readily explainable.