[Hormonal control of thyroxine-binding globulin synthesis and metabolism (author's transl)]

Serum thyroxine-binding globulin (TBG), the major plasma transport protein for thyroid hormones in man, was shown to be altered under the influence of estrogen and in hypothyroidism. In order to study these alterations, we used an animal model. Synthesis of TBG was demonstrated in hepatocytes isolated from adult Rhesus monkeys, and in a monkey hepatocarcinoma continuous cell culture line (NCLP-6-E). When the hepatocytes were obtained from monkeys pretreated with beta-estradiol (E2), a specific 2.5-2.9 fold increase of TBG synthesis and secretion was shown; similar data were obtained with the tumor line. Furthermore, an increased TBG production was shown with these cells when T4 (from 10(-14) to 10(-11) M) was added to the culture medium. The in vitro results were correlated with in vivo data obtained by investigating the metabolism of TBG after iv injection of tracer doses of purified, radiolabelled TBG to normal, E2-treated and thyroidectomized monkeys. The main effect of estrogen administration was a marked increase of the production rate. During hypothyroidism, the catabolism and the production rate of TBG were decreased. In both conditions, there were significant changes in the distribution volume of TBG, the physiologic relevance of which remains to be investigated.