PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “DIIODOTYROSINE”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 685 records · Page 38Linked to original sources
PubMed1973

Demonstration of iodide transport defect but normal iodide organification in nonfunctioning nodules of human thyroid glands.

Benign and malignant nodules in human thyroid glands, which did not concentrate iodide in vivo, were also unable to accumulate iodide in vitro. The mean thyroid-to-medium ratio (T/M) in seven benign nodules was 0.8+/-0.2 compared with 7+/-2 in adjacent normal thyroid tissue. In four malignant thyroid nodules, the mean T/M was 0.5+/-0.1 compared with 11+/-4 in adjacent normal thyroid. Despite the inability of such nodules to concentrate iodide, iodide organification was present but was only one-half to one-third as active as in surrounding normal thyroid. Thyroid-stimulating hormone (TSH) increased iodide organification equally in both benign nodules and normal thyroid although it had no effect in three of the four malignant lesions. The reduction in organification is probably related to the absence of iodide transport, since incubation of normal thyroid slices with perchlorate caused similar diminution in iodide incorporation but no change in the response to TSH. Monoiodotyrosine (MIT) and di-iodotyrosine (DIT) accounted for most of the organic iodide in both the nodules and normal tissue. The MIT/DIT ratio was similar in normal and nodule tissue. The normal tissue contained much more inorganic iodide than the nodules, consistent with the absence of the iodide trap in the latter tissue. The thyroxine content of normal thyroid was 149+/-17 mug/g wet wt and 18+/-4 mug/g wet wt in the nodules. The transport defect in the nodules was not associated with any reduction in total, Na(+)-K(+)- or Mg(++)-activated ATPase activities or the concentration of ATP. Basal adenylate cyclase was higher in nodules than normal tissue. Although there was no difference between benign and malignant nodules, the response of adenylate cyclase to TSH was greater in the benign lesions. These studies demonstrate that nonfunctioning thyroid nodules, both benign and malignant, have a specific defect in iodide transport that accounts for their failure to accumulate radioactive iodide in vivo. In benign nodules, iodide organification was increased by TSH while no such effect was found in three of four malignant lesions, suggesting additional biochemical defects in thyroid carcinomas.

Adenoma↗
PubMed1977

A simple synthesis of [3,5-125I]Diiodo-L-thyroxine of high specific activity.

The customary methods for labeling T4 And its analogs, iodination or exchange-labeling, are not applicable to those iodothyronines whose iodine atoms are exclusively in the nonphenolic ring. Therefore, [3,5-125I]Diiodo-L-thyronine had to be synthesized by a different metnod. This synthesis involves the coupling of [125I]diiodo-L-tyrosine with 4-hydroxy-3,5-diiodophenylpyruvic acid to form L-thyroxine labeled in the nonphenolic ring, followed by removal of the two unlabeled iodine atoms in the phenolic ring. High specific activity, limited only by that of the [125I]diiodo-L-tyrosine used as starting material, can be achieved. Radioactivity yields are approximately 36% in the coupling reaction and approximately 86% in the deiodination reaction, amounting to an overall yield of greater than 30%. L-Thyroxine and 3,5-diiodo-L-thyronine were purified by ion-exchange chromatography. Their radiochemical purity was checked by radiochromatography.

Diiodotyrosine↗
PubMed1986

Characterization and purification of iodinated bovine thyrotropin by high performance liquid chromatography.

Reversed-phase (RP) HPLC, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and gel permeation chromatography have been used to study the incorporation of 125I into bovine (b) TSH by the lactoperoxidase-catalyzed radioiodination procedure. Two preparations of [125I]bTSH were studied, being freshly iodinated bTSH and tracer purified from this preparation by the method of receptor adsorption. It is demonstrated with these methods that both the alpha- and beta-subunits of bTSH are labeled with 125I, and that the tracer purified by receptor adsorption retains this incorporation pattern. However, the implied theoretical specific activity of (at least) 2 I atoms per TSH molecule (or approximately 140 muCi/micrograms) suggested by this result was not achieved, with observed tracer specific activity being 30-60 muCi/micrograms, indicating that hormone molecules with varying extents of labeling must exist. Evidence to support this was provided by comparison of the MIT/DIT ratios for the 2 tracer preparations. Receptor adsorption decreased the MIT/DIT ratio from 75:25 in the freshly iodinated bTSH to 93:7, indicating the selection of particular iodinated species. Tryptic mapping by RP-HPLC was used to study both tracer preparations, and it is shown that at least 14 iodine-containing tryptic peptides may be resolved for each preparation, which is greater than the theoretical maximum of 13 peptides if every tyrosine was labeled and tryptic cleavage occurred at all possible lysine and arginine residues. Tracer heterogeneity was also studied by purification using RP-HPLC. Selection of peak fractions demonstrated that intact [125I]bTSH may be recovered from RP-HPLC which in TSH radioreceptor assay exhibit increased assay sensitivity, increased saturable binding, and decreased nonsaturable binding.

Animals↗
PubMed1986

Inhibition of follicle-stimulating hormone induction of aromatase activity in porcine granulosa cells by thyroxine and triiodothyronine.

We examined the effects of T3 and T4 on basal and FSH-induced aromatase activity in granulosa cells isolated from medium-sized follicles (4-6 mm) of prepubertal pigs. Treatment of cells with T3 or T4 alone during an initial 48-h induction period did not result in any significant change in aromatase activity, as measured by 17 beta-estradiol accumulation during the subsequent 6-h test period, when testosterone (0.5 microM) was added as substrate. However, when cells were cultured with FSH and T3 or T4 during the induction period, a definite dose-dependent inhibition of FSH-induced aromatase activity was demonstrated. This inhibition was not altered by the presence of a binding protein (BSA). The inhibition of FSH-induced aromatase activity by T4 and T3 is a true biological effect, as inactive iodocompounds (MIT and DIT) and iodide had no significant effect on the gonadotropin-induced aromatase activity. Furthermore, the viability of cells was unaffected by the thyroid hormones, and total cellular protein did not change significantly. These results indicate that thyroid hormones might play an important role in modulating FSH-induced aromatase activity, and that the elevated plasma estrogen levels in some cases of hyperthyroidism are not due to increased ovarian secretion.

Animals↗