3,3′,5′-Triiodothyronine (rT3) Inhibits Iodothyronine-5′-Deiodinating Activity Induced by Equimolar Concentration of 3,5,3′-Triiodothyronine (T3) in Cultured Fetal Liver of Mouse
rT3 is generally considered to be without thyroid hormone activity at physiological concentrations and to play no significant physiological role. However, several agonistic and antagonistic effects of rT3 were reported at supraphysiological doses (1,2). As is well known, there exists little or no iodothyronine-5′-deiodinating activity (I-5′-DA) in the fetal liver of rodents (3). The enzyme activity rapidly increases after birth and peaks at 3–4 weeks in the case of mouse (4). We recently demonstrated that this ontogenetic development of iodothyronine-5′-deiodinase in the liver can also be induced in vitro by physiological concentrations of glucocorticoid and thyroid hormones (5). To investigate the rT3 effect on I-5′-DA, fetal liver of mouse on the 19th day of gestation, in which little or no I-5′-DA was detected and, therefore, rT3 was very stable, was cultured for 3–15 days, and I-5′-DA was determined in liver homogenate.
KeywordsThyroid Hormone Fetal Liver Liver Homogenate Thyroid Hormone Activity Supraphysiological Dose
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