Reference

Decrease in triiodothyronine binding sites in chick embryo erythrocytes during early development

Decrease in triiodothyronine binding sites in chick embryo erythrocytes during early development. Dasmahapatra, A. K.; Thomas, C. R.; Frieden, Earl (Dep. Chem., Florida State Univ., Tallahassee, FL 32306-3006, USA). Dev. Biol., 120(2), 412-17 (English) 1987. CODEN: DEBIAO. ISSN: 0012-1606. DOCUMENT TYPE: Journal CA Section: 2 (Mammalian Hormones) Specific thyroid hormone (TH) binding sites were detected in nuclei of erythrocytes obtained from developing chick embryos. The binding characteristics and relative affinities for TH analogs were those expected of TH receptors. Nuclear triiodothyronine (T3) [6893-02-3] satn. anal. was carried out in vitro by incubating intact erythrocytes in M199 medium with 3-200 pM [125I]T3 for 1 h at 37° or 20-24 h at 21°. Nuclei were obtained by centrifugation after lysing the erythrocytes in a stabilizing buffer contg. 0.3% saponin, followed by addn. of Triton X 100 (final concn. 0.2%) to minimize the nonspecific binding. Scatchard anal. of equil. binding data suggested that the nuclei possess a single class of binding sites. The binding is reversible and the rate of dissocn. is temp.-dependent. T3 and T4 [51-48-9] appear to bind to the same sites, but the affinity of T3 was 16 times greater. 5817-39-0 and 67-30-1 which are cas registry numbers of chemicals are mentioned. Among TH analogs tested, Triac [51-24-1] had the highest affinity followed by L-T3, D-T3 [5714-08-9], Tetrac [67-30-1], L-T4, D-T4 [51-49-0], T2 [1041-01-6], and rT3 [5817-39-0]. Serial studies performed on different days of chick embryogenesis demonstrated a rapid and significant decrease of the erythrocyte nuclear T3 receptor. On day 5, the no. of T3 binding sites was maximal at 1600/nucleus. The no. declined steadily until, by day 20, it had reached about 60 sites/nucleus. Erythrocytes from adult and baby chickens had <1% as many binding sites as those from day 5 embryos. There was no significant change in the affinity of the sites (Kd = 20 pM at 37°). The reason for the loss of T3 binding sites during embryogenesis is not known. Since the plasma level of the TH increases during embryogenesis, this may reflect downregulation. Alternatively, the change in erythrocyte population which occurs during this period involves prodn. of erythrocytes which contain fewer T3 binding sites. .

Stimulation of liver iodothyronine monodeiodinases is not direct action of TSH

Stimulation of liver iodothyronine monodeiodinases is not direct action of TSH. Wu, Sing Yung; Chang, Tien Chun; Chang, Ching Chung; Chen, Fang Wu (Nucl. Med. Serv., Veterans Adm. Med. Cent., Long Beach, CA, USA). T'ai-wan I Hsueh Hui Tsa Chih, 85(10), 941-6 (English) 1986. CODEN: TIHHAH. ISSN: 0371-7682. DOCUMENT TYPE: Journal CA Section: 2 (Mammalian Hormones) Thyroid and hepatic iodothyronine monodeiodinases were stimulated following TSH [9002-71-5] treatment for 3 consecutive days in rats. T3 [6893-02-3] treatment (25 mg, t.i.d.) for 3 consecutive days markedly stimulated hepatic deiodinases; T3 conversion from T4 [51-48-9] rose to 5.6-fold and T2 [1041-01-6] conversion from T3 rose to 3.7-fold of that in the saline control. Thyroid conversion of T4 to T3 and T3 to T2, on the other hand, decreased significantly after T3 treatment. Evidently, TSH-mediated induction of thyroid monodeiodinases is a direct effect of TSH, whereas the hepatic enzymes are stimulated secondarily by the increase of circulating thyroid hormones. Thus, iodothyronine monodeiodinases in the thyroid, which are readily inducible by TSH, may be important in adaptation to hypothyroidism by activating the thyroid hormone. In contrast, liver, having marked enzyme activity in hyperthyroidism and reduced enzyme activity in hypothyroidism, may be important in deactivating the thyroid hormone (detoxication) in thyrotoxic states when the enzyme activity is high.Except for chemicals metioned above, 51-48-9 and 70712-46-8 are also used. .