Trans isomers of long-chain n-3 polyunsaturated fatty acids in tissue lipid classes of rats fed with heated linseed oil.

The isomerization of linolenic acid into mono- and di-trans isomers takes place during heat treatment. One of these compounds, 18:3 delta 9c, 12c, 15t can be desaturated and elongated to form, in particular, the trans isomers of eicosapentaenoic and docosahexaenoic acids. This study was undertaken to observe the incorporation of these trans long-chain n-3 polyunsaturated fatty acids into the lipid classes of several tissues. Rats were fed for 8 weeks with heated linseed oil containing high levels of trans linolenic acid isomers. The lipid classes of the liver, kidney, heart and adrenals of these rats contained various levels of these compounds. The 20:5 delta 5c, 8c, 11c, 14c, 17t represented between 80 and 90% of the total 20:5 in the phospholipids, but 22:5 delta 7c, 10c, 13c, 16c, 19t and mainly 22:6 delta 4c, 7c, 10c, 13c, 16c, 19t were only present in small quantities. This may indicate that the cis fatty acids are better metabolized in these cases. Among the tissues studied, it was interesting to note a high level of 22:5 delta 19t in the adrenals, particularly in cholesterol esters.