Changes in lipid composition of calf tissues by excess dietary zinc

In a previous study, very high Zn (1000 ppm) prevented most of the tissue lipid increases caused by very high Cu (1000 ppm), and this investigation was conducted to study whether Zn had a direct effect on lipid metabolism or simply acted indirectly by inhibiting excess Cu activity. Calves were fed basal dietary Cu (10 ppm), and lipid composition of heart, liver, and blood plasma was measured as affected by control (40 ppm in DM), high (500 ppm), or very high (1000 pm) Zn intakes. Supplementation with 1000 ppm of Zn did not cause any marked quantitative changes in tissue lipids (e.g., lipid classes, oleic, or stearic acids), suggesting that, in the previous study, Zn had mainly interfered with excess Cu effects on lipids rather than with lipid metabolism directly. However, there were two exceptions. Adding 1000 ppm of Zn to basal Cu ration 1) reduced concentration and changed the fatty acid composition of plasma cholesterol esters, both of which are indicative of excess Zn inhibiting lecithin:cholesterol acyltransferase activity, and 2) altered the desaturation and elongation of the essential fatty acids and their concentration in tissue phospholipids. This latter effect of excess Zn conceivably could be important in changing the structure and function of cell membranes and in the production and activity of prostanoids and leukotrienes.