Effect of dietary protein level and thyroxine on vitamin A depletion from liver in chicks.

I . The effect of dietary protein level and supplementation with thyroxine and thiouracil on depletion of liver stores of vitamin A, on the percentage of liver vitamin A in the alcohol form and on the plasma level of vitamin A and protein has been studied in chicks. In an experiment with cockerels the relation was investigated between the vitamin A level of plasma and the electrophoretic pattern of its proteins. 2. Liver vitamin A depletion was considerably reduced by lowering the dietary protein level. 3. Protein malnutrition lowered the percentage of vitamin A found in the liver in the alcohol form. 4. Depletion of vitamin A from the liver was related to the percentage of vitamin A in the alcohol form. 5 . Thyroxine increased both vitamin A depletion from the liver and the percentage of vitamin A in the alcohol form, whereas thiouracil had the opposite effect. 6. Plasma vitamin A, and plasma protein contents were significantly lowered in cockerels receiving a 5 % protein diet. The drop in plasma protein level was essentially caused by a reduction of the albumin fraction. No significant change in the levels of globulins was observed even after a +week period of protein malnutrition. 7. When the dietary protein level was restored to normal both the albumin and vitamin A levels in plasma increased.