The protective action of vitamin A upon various tissues in the avitaminotic rat, and the sensitivity of these tissues to vitamin A deficiency

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Abstract
Changes occurring in the incisor teeth, medulla oblongata, the maxillary fundic alveolar bone, and the nasolacrimal duct in rats were examined after the animals had been subjected to various regimens of dietary vitamin A. Thirty rats receiving a vitamin A-free diet from 7 days pre-weaning showed marked degenerative changes of the medulla and epithelia at 28 days post weaning, when the incisors and maxillary fundic bone were only slightly affected. By 49 days post weaning all structures examined showed advanced changes. The funiculus praedorsalis, incisor tooth and fundic bone were all protected to 50 days by 1 I.U. vitamin A daily, but the epithelium was not protected until the dally dosage was 3 I. U. Over longer periods (100-250 days) the funiculus praedorsalis was protected and the fundic bone almost completely protected by 2 I.U. vitamin A daily. The epithelium was protected by 4 LU. daily but the incisor tooth was totally unprotected by 2 I.U. daily and not entirely protected by 16 I. U. daily. The results show that relative sensitivity of various tissues to vitamin A-lack and that the degree of response to dosage with the vitamin are different at different ages. The requirement for vitamin A is probably not a function of body weight, but rather a measure of the protection of that tissue most sensitive to vitamin A deficiency at any particular age.