Quantitative measurements of dietary and [1-14C]linoleate metabolism in pregnant rats: specific influence of moderate zinc depletion independent of food intake.

Our objective was to investigate whether the effects of moderate zinc deficiency on metabolism of linoleate during pregnancy could be distinguished from the effects of low food intake. Rats were force-fed an isoenergetic zinc-deficient (3.2 mg/kg) or control (26.4 mg/kg) semiliquid diet during the second half of pregnancy. Fatty acid quantity and composition in both maternal and fetal organs were analyzed at term. Recovery of 14C in lipid- and water-soluble metabolites from orally injected [1-(14)C]linoleate was also studied. After 10 days of gavaging identical amounts of the diet, zinc-deficient rats had lower serum zinc and lower uterus and placenta weights than controls, but body weights were similar. At term, zinc-deficient rats had a fatty acid composition in organs and carcass similar to that of the controls, but the zinc-deficient fetuses had lower long-chain n-6 and n-3 polyunsaturates in brain, liver, and carcasses. Lipids extracted from most organs of zinc-deficient rats contained lower 14C levels, but 14C was raised in the maternal carcass lipids and in water-soluble metabolites. We conclude that zinc deficiency during pregnancy increases oxidation of linoleate and decreases synthesis or transport of polyunsaturates to the fetuses and that these effects are independent of depressed food intake, i.e., they are specific to zinc depletion. Thus, zinc deficiency has distinct effects on fatty acid metabolism, which are readily observed using 14C tracer methods.