We studied the dependence of the free thyroxin (T4) index and the ratio of T4 to thyroxin-binding globulin (TBG) on TBG concentrations, using sera from cases of congenital TBG deficiency and congenital TBG excess. Two such sera with similar concentrations of albumin, transthyretin, and free T4 were mixed to provide test samples with TBG concentrations covering the range of clinical interest wit...

The contribution of L-thyroxine (T4) to nuclear thyroid receptor occupancy was studied in GC cells incubated with concentrations of 3,5,3'-triiodo-L-thyronine (T3) and T4 that resulted in free iodothyronine levels similar to those in serum of euthyroid rats. T4 accounted for 5.4-10% of the occupied receptors: T3 derived from T4 [T3(T4)] and T3 added to medium accounted for the remainder of rece...

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Blind hamsters had no alteration of the dialyzable fraction of serum thyroxine (T4) but had depressed total and free T4 concentrations compared to controls. Prevention of the effects of blinding by pinealectomy indicates pineal influence on circulating free T4 concentration. Parallel changes in free T4 and the free T4 index indicate adequacy of the index in representing pineal-induced changes i...

There have been, and continue to be, reports of discordant free thyroxine (T4) 3 measurements when different free-T4 methods are applied to the same serum samples (1– 4 ). Our laboratory has attempted to identify some of the factors that contribute to these disparities. There are 4 separate components of serum T4: free T4, albumin-bound T4, transthyretin-bound T4, and thyroxine-binding globulin...

1. Effects of endosulfan, malathion and carbaryl on circulating T4, T3 and T3/T4 ratio in the freshwater catfish, C. batrachus have been studied during reproductively active phases, i.e. vitellogenic and post-vitellogenic phases of its annual reproductive cycle. 2. Endosulfan provoked a significant increase in T4 and a decrease in T3 as well as the T3/T4 ratio. 3. Malathion decreased T3 and T3/...