Effect of dietary protein level and thyroxine on vitamin A absorption and on plasma proteins in chicks

Abstract

1. The effect of dietary protein level and supplementation with thyroxine on the liver storage of vitamin A, on the fraction of liver vitamin A in the alcohol form, and on the plasma levels of vitamin A and proteins has been studied in chicks.2. Liver storage was reduced by lowering the dietary protein level.3. Protein restriction lowered the percentage of vitamin A found in the liver as retinol.4. Thyroxine increased both vitamin A storage and the fraction of the total vitamin A as retinol, this effect being dependent on dietary protein level.5. Plasma vitamin A and plasma protein contents were lowered to a highly significant extent by protein restriction. This drop was essentially caused by reduction of the albumin fraction in chicks fed on a 5% protein diet and by a reduction of β- and γ-globulins in chicks fed on a 10% protein diet.6. Thyroxine supplementation of the diet lowered to a highly significant extent plasma protein content; this reduction was caused by a dramatic fall in the level of plasma albumin. The β- and γ-globulins were concomitantly increased.