A comparison of the lipid compositions of the lipoproteins of the intestinal and popliteal lymph and plasma of sheep

Abstract

The lipids and lipoproteins of intestinal lymph in the sheep make a contribution to the corresponding fractions in plasma and thence affect lipid compositions in other tissues. As a first step towards assessing this contribution, the lipoproteins of intestinal lymph, peripheral (popliteal lymph) and plasma have been isolated for compositional studies. Popliteal lymph and the plasma were similar in the distributions of lipids among the major lipoprotein fractions with high-density lipoproteins accounting for just over half of the total lipid present. In intestinal lymph, 80 per cent of the total lipid was associated with the very low-density lipoprotein fraction. Whereas triacylglycerols comprised the principal lipid component of the very low-density lipoprotein and low-density lipoprotein fractions of the intestinal lymph and were present in the high-density lipoprotein fraction, they were present in essence only in the very low-density lipoprotein fraction of popliteal lymph and plasma, where high concentrations of cholesteryl esters and phospholipids were found in all the lipoprotein fractions. The fatty acid compositions of each lipid class were also determined. The most distinctive feature of the results was the distribution of the essential fatty acid, linoleic acid, among the lipid components. In all lipid classes in each of the body fluids, the concentration of this component was highest in the high-density lipoproteins and lowest in the very low-density lipoproteins. Higher concentrations tended to be present in the triacylglycerols and phosphatidylcholine fractions of intestinal lymph than of plasma and popliteal lymph, but the opposite was true of the cholesteryl esters. The results are discussed in terms of the sources of the linoleic acid in the lipids of intestinal lymph of ruminant animals.