Zinc deficiency reduces hepatic cellular retinol-binding protein in rats

Hepatic cellular retinol-binding protein (cRBP) levels were measured from the livers of four groups of Sprague-Dawley rats after three weeks of dietary treatment. The experimental group (n = 8) received a zinc-deficient (2.3 mg/kg dry powder) liquid diet ad libitum. A pair-fed control group (n = 8) received the same amount of liquid diet with supplemental zinc (60 mg/kg dry powder). Another control group (n = 8) received liquid diet ad libitum with supplemental zinc (60 mg/kg powder). A third control group (n = 7) received a pellet diet which also contained the same amount of zinc as the other control groups (60 mg/kg). Hepatic cRBP was reduced by more than 50% in the experimental group as compared to each of three control groups. It appears that zinc may be an essential element for the intra-cellular transport of vitamin A, in addition to its well-established role in the intercellular transport of vitamin A.