Change in vitamin A content in tissues of rats fed on a vitamin A-free diet.

The effect of the feeding of a vitamin A-free diet on vitamin A metabolism was studied in rats by following changes in tissue distribution of the vitamin for 24 days. The serum level of vitamin A was maintained at a constant level until the last day of the experiment, by which time the liver reserve had declined to as low as one-seventh of its initial value. In contrast, the concentration of vitamin A in the kidney increased gradually in rats fed on a vitamin A-free diet and rose to levels higher than those in the liver after 24 days, whereas the kidney vitamin A concentration in the control animals remained at a constant level. In the testis, total vitamin A content increased in both the control group and that fed on a vitamin A-free diet. However, the magnitude of increase was smaller in the latter than in the former. Replenishment of the vitamin-A depleted rats with the vitamin provoked a prompt restoration of all changes produced by feeding of the depleted diet. Possible roles of the kidney are discussed with respect to homeostatic maintenance of the vitamin in vitamin A-depleted animals.