The effect of zinc deficiency on the metabolism of retinol-binding protein in the rat.

Abstract Zinc-deficient rats have very low plasma vitamin A levels in spite of adequate liver vitamin A stores. A study was conducted to explore the effects of zinc deficiency on the metabolism of retinol-binding protein (RBP), the plasma transport protein for vitamin A. The plasma RBP level of zinc-deficient rats was only 14 ± 2 μg per milliliter In contrast, the plasma RBP level was 50 ± 2 μg per milliliter in control rats fed ad libitum on a zinc-sufficient diet and 36 ± 1 μg per milliliter in a zinc-sufficient group pair-fed with the zinc-deficient rats. Moreover, the liver RBP levels of the zinc-deficient group were only about 55 to 60 per cent of the levels of either the ad libitum or pair-fed control animals. The data suggest that zinc deficiency interferes with the synthesis of RBP by the liver and probably with the synthesis of some other plasma proteins as well. The low plasma vitamin A levels seen in zinc deficiency can be attributed to an impaired ability of the deficient rat to mobilize vitamin A from its liver in the form of the retinol-RBP complex.