|Title:||Stimulation of liver iodothyronine monodeiodinases is not direct action of TSH||Authors:||WU, SING-YUNG
|Keywords:||T4;T3;deiodinases;TSH;thyroid;liver||Issue Date:||1986||Journal Volume:||v.85||Journal Issue:||n.10||Start page/Pages:||941-946||Source:||Journal of the Formosan Medical Association||Abstract:||
Thyroid and hepatic iodothyronine monodeiodinases were stimulated following THS treatment for 3 consecutive days in rats. It was questioned whether these thyroidal enzyme were induced secondarily by the elevated circulating thyroid hormone after TSH treatment or by a direct action of TSH. The present study showed that T3 treatment (25μg, t.i.d.) for 3 consecutive day markedly stimulated hepatic deiodinases; T3 conversion from T4 rose to 5.6-fold and T2 conversion from T3 rose to 3.7-fold of that in the saline control (P<0.0001 in both cases). Thyroid conversion of T4 to T3 and T3 to T2, on the other hand, decreased significantly after T 3 treatment. It is thus concluded that TSH-mediated induction of thyroid monodeiodinases is a direct effect of TSH; whereas the hepatic enzymes are stimulated secondarily by the increases of circulating thyroid hormones. It appears that iodothyronine monodeiodinases in the thyroid, which are readily inducible by TSH, may be important to an animal’s adaptation to hypothyroidism by activating the thyroid hormone. In contrast, liver having marked enzyme activity in hyperthyroidism and reduced enzyme activity in hypothyroidism my be important in deactivating the thyroid hormone (“detoxication”) in thyrotoxic states when the enzyme activity is high.
|Appears in Collections:||醫學系|
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