1. The effects of retinol and retinoic acid supplementation of retinol-deficient rats were studied for a variety of metabolic processes shown to be affected by retinol deficiency.
2. Retinol-deficient rats were found to have decreased body-weight, liver and testes weights, a degeneration of testicular germinal cells, an increased incorporation of labelled choline into liver and testes phospholipids, an increased protein synthetic activity (in vitro) of liver ribosomes, an increased transfer-RNA methyltransferase activity in liver and a decreased activity in testes, an increased DNA content of testicular nuclei, and a decreased uptake of [3H]thymidine by testicular nuclear DNA.
3. In retinol-deficient rats supplemented for 8 weeks with retinol these changes were reversed, measurements returning to control levels.
4. In retinol-deficient rats supplemented for 8 weeks with retinoic acid all changes were reversed except those in the testes.
5. Testicular signs of retinol deficiency appeared to be delayed when retinoic acid was added to the retinol-deficient diet of weanling rats. This suggests a sparing action of retinoic acid on the rat's utilization of retinol.
6. Suggestions are offered as to why retinoic acid will support growth and development but not spermatogenesis in the rat.