Influence of Zinc Deficiency on Retinal Reductase and Oxidase Activities in Rat Liver and Testes

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Abstract
The influence of zinc deficiency on vitamin A metabolism in rats was investigated by assessing two specific enzymes involved in its metabolism viz retinal reductase and retinal oxidase in the liver as well as in the testes. The activity of retinal reductase in the liver was not altered in zinc deficiency. Retinal oxidase activity on the other hand, was increased approximately 1.5 fold over the pair-fed controls. In contrast, both retinal reductase and oxidase in the testes were decreased during zinc deficiency. The effects of zinc deficiency on vitamin A metabolism in the liver could be partly attributed to the secondary effect of reduced food intake and growth. However, the effects seen in the testes on the metabolic enzymes of vitamin A appear to be due to zinc deficiency per se. The liver concentration of vitamin A (µg/g) as well as total vitamin A (µg/liver) were higher in the zinc-deficient rats when compared to the zinc-sufficient rats although not significantly different from the pair-fed controls. In agreement with previous reports, the plasma vitamin A in zinc-deficient rats were found to be markedly lowered compared to zinc sufficient ad libitum controls.