Iodothyronine Metabolism in Rat Liver Homogenates

Abstract

A B S T R A C T To investigate mechanisms of extrathyroidal thyroid hormone metabolism, conversion of thyroxine (T4) to 3,5,3'-triiodothyronine (T3) and degradation of 3,3',5'-triiodothyronine (rT3) were studied in rat liver homogenates. Both reactions were enzymatic. For conversion of T4 to T3, the Km of T4 was 7.7 ,uM, and the Fasting resulted in inhibition of T4 to T3 conversion and of rT3 degradation by rat liver homogenates which was reversible after refeeding. Serum T4, T3, and thyrotropin concentrations fell during fasting, with no decrease in serum protein binding as assessed by a T3-charcoal uptake. There was no consistent change in serum rT3 concentrations. Dexamethasone had no effect in vitro. In vivo dexamethasone administration resulted in elevated serum rT3 concentrations after 1 day, and after 5 days, in inhibition of T4 to T3 conversion and rT3 degradation without altering serum T4, T3, or thyrotropin concentrations. Endotoxin treatment had no effect of iodothyronine metabolism in liver homogenates. In kidney homogenates the reaction rates and response to propylthiouracil in vitro were similar to

Effects of administration of iron, iodine and simultaneous iron-plus-iodine on the thyroid hormone profile in iron-deficient adolescent Iranian girls

“…It is not yet clear how iron deficiency exerts its effects on deiodinase activity. Kaplan and Utiger have shown that outer ring deiodinase activity is not affected by either ferrous or ferric ions in an in vitro incubation method (Kaplan and Utiger, 1978). This, of course, does not rule out the possibility that iron needs to be incorporated into the enzyme during synthesis.…”

Triiodothyronine induces lipid oxidation and mitochondrial biogenesis in rat Harderian gland

“…IOPA inhibits all three types of deiodenase enzymes. Although the effect of IOPA is strong on type II and III, it is comparatively weak on type I (Kaplan & Utiger 1978, St Germain 1994. At the end of this treatment, 15 hypothyroid rats were killed and the remaining 15 hypothyroid rats received daily injections for 2 weeks of 15 mg T 3 /100 g body weight (Sigma-Aldrich Corp.).…”

Neonatal levels of plasma thyroxine in male and female calves fed a colostrum or immunoglobulin diet or fasted for the first 28 hours of life

“…This may be because not enough samples were studied or that they were not collected at the exact postpartum time when the transient rise occurred. On the contrary, the frequent and precise sampling practiced by Davicco et al (1982) (Balsam and Ingbar, 1979 ;Kaplan and Utiger, 1978 ;Naito et al, 1981) and piglets (Slebodzinski et al, 1982), has been shown to result in a decrease of circulating T3 in these species (Chopra, 1980 ;Hastings and Zeman, 1979 ;Heinen et al, 1981 andSlebodzinski et al, 1982, respectively) ; this phenomenon has also been shown in humans (Azizi, 1978 ;Burman et al, 1979 ;Suda et al, 1978), adult sheep (Blum et al, 1980), growing bulls Tveit and Almlid, 1980), deer (Bahnak et al, 1981), chickens (May, 1978) …”