Vitamin A metabolism during the repletion of zinc deficient rats

The experiments reported here were designed to determine if the low plasma vitamin A levels observed in zinc deficient rats are reversible as well as to examine the time required for any response. In experiment 1, rats previously zinc deficient were repleted for 6 days with a zinc sufficient diet, fed either ad libitum, or pair-fed the amount consumed by a zinc deficient group. After repletion, plasma vitamin A concentration for the zinc sufficient group returned to within normal range while the pair-fed group had a plasma vitamin A concentration intermediate between the zinc sufficient ad libitum and zinc deficient groups. The zinc sufficient ad libitum group had a lower concentration but higher total liver content of vitamin A than the other two groups. In experiment 2, the response of zinc deficient rats to intraperitoneal zinc repletion was examined daily for 7 days. There was a 3 day lag period before plasma vitamin A began to increase significantly following zinc treatment. By the fifth day, plasma vitamin A concentration increased to within the normal range. The data suggest that adequate food intake as well as zinc appears necessary to totally reverse low plasma vitamin A concentrations in zinc deficiency. Possible mechanisms are discussed.