ZINC-DEFICIENCY AND THE DESATURATION OF LINOLEIC-ACID IN RATS FORCE-FED FAT-FREE DIETS

Recent studies with rats force-fed zinc-deficient diets containing var ious types of fat failed to demonstrate a role of zinc in desaturation of linoleic acid. The present study was conducted to investigate the effect of zinc deficiency on desaturation of linoleic acid in rats tha t were initially force-fed fat-free diets to stimulate activity of des aturases. Therefore, rats were fed zinc-adequate and zinc-deficient fa t-free diets for 6 d. After that period, the groups were divided and h alf of the rats continued feeding the fat-free diet for another 3.5 d whereas the other half was switched to a fat diet by supplementing the fat-free diet with 5% safflower oil. Ln order to assess desaturation of linoleic acid, fatty acid compositions of liver phosphatidylcholine , -ethanolamine, and -serine were considered, particularly levels of i ndividual (n-6) polyunsaturated fatty acids (PUFA). Levels of total an d individual (n-6) PUFA were similar in zinc-adequate and zinc-deficie nt rats fed the fat-free diet throughout the experiment. Addition of 5 % safflower oil increased levels of total and individual (n-6) PUFA in both zinc-adequate and zinc-deficient rats. However, total (n-6) PUFA in all types of phospholipids were higher in zinc-adequate rats than in zinc-deficient rats. Additionally, in zinc-deficient rats there wer e changes of (n-6) PUFA levels typical for impaired Delta 5 and Delta 6 desaturation: linoleic acid and dihomo-gamma-linolenic acid were ele vated; arachidonic acid, docosatetraenoic acid, and docosapentaenoic w ere lowered by zinc deficiency. Therefore, the study shows that zinc d eficiency impairs desaturation of linoleic acid in rats force-fed fat- free diets and therefore supports results from former convential zinc deficiency experiments suggesting a role of zinc for desaturation of l inoleic acid.