Thyroidal control of heaptic release and metabolism of vitamin A.
The inverse relationship that exists between thyroxine and the vitamin A level of plasma has been examined in chicken. Thyroxine treatment leads to a decrease in the level of vitamin A carrier proteins, retinol-binding protein and prealbumin-2 in plasma and liver. There is an accumulation of vitamin A in the liver, with a greater proportion of vitamin A alcohol being present compared to that of control birds. In thyroxine treatment there is enhanced plasma turnover of retinol-binding protein and prealbumin-2, while their rates of synthesis are marginally increased. Amino acid supplementation partially counteracts effects of thyroxine treatment. Amino acid supplementation of thyroxine-treated birds does not alter the plasma turnover rates of retinol-binding protein and prealbumin-2 but increases substantially their rates of synthesis. The release of vitamin A into circulation is interfered with in hyperthyroidism due to inadequate availability of retinol-binding protein being caused by enhanced plasma turnover rate not compensated for by synthesis.
D000596:Amino Acids / Q000378:metabolism; D000601:Amino Acids, Essential / Q000494:pharmacology; D000818:Animals; D002645:Chickens; D006980:Hyperthyroidism / Q000378:metabolism; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D011228:Prealbumin / Q000378:metabolism; D012177:Retinol-Binding Proteins / Q000097:blood / Q000378:metabolism; D054839:Retinol-Binding Proteins, Plasma; D013961:Thyroid Gland / Q000502:physiology*; D013974:Thyroxine / Q000494:pharmacology; D014801:Vitamin A / Q000097:blood / Q000378:metabolism*
D000596:Amino Acids; D000601:Amino Acids, Essential; D011228:Prealbumin; D012177:Retinol-Binding Proteins; D054839:Retinol-Binding Proteins, Plasma; D014801:Vitamin A; D013974:Thyroxine