The effect of dietary fat on activities of lipogenic enzymes in liver and adipose tissue of zinc-adequate and zinc-deficient rats

Abstract

The aim of the present study was to investigate if zinc-deficiency influences the regulation of lipogenic enzymes by dietary polyunsaturated fatty acids. Therefore, rats were fed a fat-free diet with either adequate or deficient zinc supply for 6 days. After that period the groups were divided; half of the rats were given the fat-free zinc-adequate and zinc-deficient diets for another 3 days, whereas the other half was given the same diets supplemented with 5% safflower oil. To control food intake, all the rats were force-fed by gastric tube. At the end of the experiment, zinc-deficient rats fed both, the fat-free diet and the 5% safflower oil diet had largely reduced zinc concentrations and activities of alkaline phosphatase in serum proving their zinc-deficient state. Zinc-deficient rats fed both the fat-free and the 5% safflower oil diet had markedly increased concentrations of triglycerides in liver compared with zinc-adequate rats. Zinc-deficient rats fed both the fat-free diet and the 5% safflower oil diet had increased activities of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase compared with their controls. In contrast, activities of fatty acid synthase and malic enzyme were not changed by zinc deficiency. This suggests that fatty liver is not mainly due to increased lipogenesis but to other factors such as impaired exclusion of lipids from liver. The addition of safflower oil to the fat-free diet suppressed activities of hepatic lipogenic enzymes in both, zinc-adequate and zinc-deficient rats. However, the suppression was more pronounced in zinc-adequate rats than in zinc-deficient rats. In adipose tissue, addition of safflower oil elevated activities of lipogenic enzymes in zinc-adequate rats but lowered activities in zinc-deficient rats. Those data suggest that zinc-deficiency affects regulation of lipogenic enzymes in liver and adipose tissue.