T H E skeleton of young animals is profoundly affected by an abnormal amount of vitamin A in the body. In vitamin A deficiency changes in the functional activity of the osteoblasts and osteoclasts allow bone to be deposited in places where it would normally be removed, so producing excessive thickening of certain parts of the skeleton (Mellanby, 1938, 1939). Conversely, excessive vitamin A caus...

Vitamin A is normally transported in plasma as retinol bound to a specific protein, retinol-binding protein (RBP). Detailed studies were conducted to examine the effects of excess vitamin A on the plasma concentration and metabolism of RBP, and to obtain information about vitamin A transport in the hypervitaminotic state. Two separate experiments were conducted. In the first (Study I, 99 days),...

1. Young rats were kept for several weeks on a diet deficient in vitamin A. Some were undosed, others were given marginal (25i.u. weekly), adequate (1000i.u. weekly) or excessive (50000i.u. daily) doses of vitamin A acetate. The undosed rats developed signs of vitamin A deficiency, and the overdosed animals had skeletal fractures indicative of hypervitaminosis A. 2. The rats were decapitated. T...

In view of the theory that an excess of vitamin A causes release of cathepsins from intracellular lysosomes, hypervitaminosis A was induced orally in the larvae of Xenopus laevis. It was predicted that the tails of these amphibia would undergo resorption prior to metamorphosis, since the presence of abundant lysosomes, associated with measurable increases of catheptic activity, had previously b...

The administration of relatively large amounts of vitamin A to hypervitaminotic D rats decreases the toxicity of this condition as evidenced by increased longevity, better weight gain, decreased soft tissue calcification and by considerable improvement in the histologic appearance of osseous structures.