The free iodotyrosines of the rat thyroid gland

Pitt‐Rivers, Rosalind; Cavalieri, Ralph R.

doi:10.1042/bj0860086

Cited by 21 publications

(6 citation statements)

References 23 publications

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“…Halmi & Pitt-Rivers (1962) showed that, at short times after the injection of 131I in rats, the specific-activity curve of the second iodide pool, derived by intrathyroidal deiodination of iodo compounds, rose more steeply than that of any iodo amino acid in rat thyroglobulin (Pitt-Rivers, 1962); they postulated a heterogeneity of thyroglobulin with respect to labelled iodotyrosines, the fraction with a more rapid turnover being the probable precursor of the second iodide pool at short times after the injection of 131I. This did not preclude the possibility that all the iodotyrosine residues, whether labile or not, could be the precursors of the second iodide pool.…”

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Heterogeneity of rat thyroglobulin labelled with 131I in vivo

Pitt‐Rivers¹

1963

Biochemical Journal

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“…This did not preclude the possibility that all the iodotyrosine residues, whether labile or not, could be the precursors of the second iodide pool. Pitt-Rivers & Cavalieri (1963) made quantitative studies of 131I-labelled free iodotyrosines in diffusates of rat thyroids at different times after the injection of 1311. They found that, up to 4 hr.…”

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Heterogeneity of rat thyroglobulin labelled with 131I in vivo

Pitt‐Rivers¹

1963

Biochemical Journal

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“…Free tyrosine in the thyroid gland may be concentrated from the blood by active transport, which was shown by Raghupathy et al (1963) to occur in vitro, or it may be accumulated as a hydrolytic product within the gland. Pitt-Rivers & Cavalieri (1963) have stated that the free monoiodotyrosine, which may contribute to the second or perchlorate-nondischargeable iodide pool in the thyroid, could arise either from iodination of free tyrosine or from hydrolysis of iodinated peptides or protein. Experiments with thyroid homogenates, cells or partially purified peroxidase systems from thyroid glands (Fawcett & Kirkwood, 1953;Serif & Kirkwood, 1956;Alexander, 1959;Pastan, 1961;Klebanoff, Yip, & Kessler, 1962;De Groot & Davis, 1962) show rapid iodination of added free tyrosine.…”

Section: Discussionmentioning

confidence: 99%

“…Pitt-Rivers & Cavalieri (1963) (Fawcett & Kirkwood, 1953;Serif & Kirkwood, 1956;Alexander, 1959;Pastan, 1961;Klebanoff, Yip, & Kessler, 1962;De Groot & Davis, 1962) show rapid iodination of added free tyrosine. De Groot & Davis (1962) have shown that varying the tyrosine concentrations from 1 to 0.1 4tmole in an in vitro system containing the equivalent of 8 mg thyroid 10 MODIFICATION OF THYROID TYROSINE tissue (our calculations) will reduce the ability of the enzyme to iodinate free tyrosine by about 60 %.…”

Section: Discussionmentioning

confidence: 99%

Hormone‐induced modifications of free tyrosine in the rat thyroid gland

Hodge¹,

Melmon²,

Sjoerdsma³

1969

The Journal of Physiology

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SUMMARYThe concentrations of free tyrosine in liver, muscle, kidney and thyroid gland were determined in separate groups of rats maintained on a low iodine diet and treated with intraperitoneal iiijections of thyroxine (T 4), thyrotrophin (TSH) and TSH plus propylthiouracil (PTU). Groups of hypophysectomized rats also were given T 4. Significant changes in tissue tyrosine were generally confined to the thyroid gland. Animals treated with T 4 showed a decrease of mean thyroid tyrosine from 113-3 + 17-9 (S.D.) /sg/g wet weight of gland to 76 2 + 5*7 ,ug/g (P < 0-01). Although there was little change in content when TSH was given alone, a significant increase in tyrosine levels was observed when TSH plus PTU were administered (P < 0-01). In hypophysectomized rats thyroid tyrosine decreased and was further lowered (to 46-0 + 3-1 ,tg/g; P < 0.05) by T 4 treatment.When tyrosine concentrations were expressed in relation to ribonucleic acid (RNA) or protein content of the assayed gland, all differences in tyrosine content became greater.

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“…Unfortunately, very little is known of the transport mechanism. On the other hand, thyroglobulin hydrolysis has been rather intensively studied, and it is known that various iodinated compounds may be released at different rates during enzymatic hydrolysis (18)(19)(20)(21)(22)(23). We have found in preliminary experiments using dog thyroid homogenate that at acid pH, which is presumably also present in intracellular phagolysosomes, larger fractions of T3 and rT3 than of T4 are released during partial autolysis (24).…”

Section: Discussionmentioning

confidence: 99%

Iodothyronine Release from the Perfused Canine Thyroid following Cessation of Stimulation

Laurberg¹

1980

J. Clin. Invest.

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A B S T R A C T The kinetics of thyroid secretion after termination of stimulation by 100 ,uU/ml bovine thyroid stimulating hormone (TSH) or 5 mM cyclic AMP (cAMP) were studied using perfused canine thyroid lobes. All experiments were performed as paired comparisons, one thyroid lobe acting as a control continuing to receive infusion of the stimulator. 2.5 h after termination of TSH infusion, the secretion of thyroxine (T4), 3,5,3'-triiodothyronine (T3), and 3,3',5'-triiodothyronine (rT3) was not significantly different from that of the control lobes. After cessation of cAMP infusion, the secretion of T4 continued unaffected for -40 min. Then a gradual decline in T4 release occurred. The secretion of T3 and rT3 decreased somewhat earlier leading to a transient phase with increases in the T4:T3 and T4:rT3 ratios in the thyroid effluent.The persistently high secretion of iodothyronines despite cessation of TSH infuision is most likely the result of at continued stimulation by receptor-bound TSH. Because the clearance of intracellular cAMP is rapid and the concentration of cAMP used for stimulation in these experiments only exceeded the concentration necessary for eliciting a secretory response modestly, it is reasonable to assume that stimulation of colloid droplet formation stopped shortly after termination of cAMP infusion. The bulk of iodothyronines secreted thereafter thus originated from continued hydrolysis of thyroglobulin engulfed by the follicular cells during the preceding cAMP infusion. The pattern of an earlier decline in secretion of T3 and rT3 than of T4 from this intracellular pool of thyroglobulin points to a more rapid liberation of tri-

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The free iodotyrosines of the rat thyroid gland

Cited by 21 publications

References 23 publications

Heterogeneity of rat thyroglobulin labelled with 131I in vivo

Heterogeneity of rat thyroglobulin labelled with 131I in vivo

Hormone‐induced modifications of free tyrosine in the rat thyroid gland

Iodothyronine Release from the Perfused Canine Thyroid following Cessation of Stimulation

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