Growth hormone acutely decreases type III iodothyronine deiodinase in chicken liver.
Growth hormone (GH) increases plasma T3 and decreases plasma T4 in 18-day old chicken embryos, in newly hatched chicks and in adult chickens within 2 h after injection. The in vivo increase in T3 can be linked to an increased in vitro T3 recovery from liver homogenates incubated with T4. Specific type I and type III deiodinase tests (5'D-I and 5D-III), however, show that GH has no effect at all on the amount of hepatic type I enzyme (catalyzing T4 deiodination to T3) but acutely decreases the amount of type III enzyme (catalyzing T3 deiodination). This suggests that the GH-induced increase in plasma T3 is not due to an increased T3 production, but is the result of a decreased T3 breakdown. The lack of a stimulatory effect of GH injection in 3-day-old fed chicks might be the combined result of a low hepatic type III enzyme level and a low GH receptor availability at that stage.
Darras
V M
VM
Laboratory of Comparative Endocrinology, K.U. Leuven, Belgium.
Berghman
L R
LR
Vanderpooten
A
A
Kühn
E R
ER
D000818:Animals; D002642:Chick Embryo; D002645:Chickens; D013006:Growth Hormone / Q000494:pharmacology*; D007453:Iodide Peroxidase / Q000378:metabolism*; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D011863:Radioimmunoassay; D011986:Receptors, Somatotropin / Q000378:metabolism; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
D011986:Receptors, Somatotropin; D014284:Triiodothyronine; D013006:Growth Hormone; D007453:Iodide Peroxidase; D013974:Thyroxine