Reduced plasma T, concentrations in sex-linked dwarf chickens appear to result from aberrant hepatic metabolism of T4 and/or T,.
This is thought to be due to a lack of growth hormone(GH) inhibition of hepatic type III deiodinase (IRD-III) activity [catalyzing T, to reverse (r)T,
and Ts to 3,3’-diiodothyronine (T2) conversion] since GH can inhibit in vitro chick liver IRDI activity (3).
Several authors have reported higher GH levels in dwarf birds, both laying-type
and broiler, particularly within the first 9 weeks of age (2,4).
This has been attributed to a defect in ,the dwarf GH receptor which results in GH resistance, (5-8). The result of such a defect would explain the Laron-type dwarfism endocrine abnormalities in sex-linked dwarf